U.S. patent application number 13/737526 was filed with the patent office on 2013-06-13 for direct digital speaker apparatus having a desired directivity pattern.
This patent application is currently assigned to Audio Pixels Ltd.. The applicant listed for this patent is Audio Pixels Ltd.. Invention is credited to Yuval COHEN, Shay Kaplan, Daniel Lewin, Alex Sromin, Yan Wool.
Application Number | 20130148827 13/737526 |
Document ID | / |
Family ID | 38476118 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130148827 |
Kind Code |
A1 |
COHEN; Yuval ; et
al. |
June 13, 2013 |
DIRECT DIGITAL SPEAKER APPARATUS HAVING A DESIRED DIRECTIVITY
PATTERN
Abstract
Direct digital speaker apparatus receiving a digital input
signal and generating sound accordingly, the apparatus including:
(a) an array of pressure-producing elements; and (b) a controller
operative to compute a timing pattern determining if and when each
pressure-producing element is actuated so as to achieve a desired
directivity pattern; wherein said pressure-producing elements have
the same amplitude.
Inventors: |
COHEN; Yuval; (Rehovot,
IL) ; Kaplan; Shay; (Givat Ela, IL) ; Lewin;
Daniel; (Tel Aviv, IL) ; Sromin; Alex;
(Ashdod, IL) ; Wool; Yan; (Gan Yavneh,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Audio Pixels Ltd.; |
Tel Aviv |
|
IL |
|
|
Assignee: |
Audio Pixels Ltd.
Tel Aviv
IL
|
Family ID: |
38476118 |
Appl. No.: |
13/737526 |
Filed: |
January 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12601427 |
Nov 23, 2009 |
8374056 |
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PCT/IL2007/000618 |
May 21, 2007 |
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13737526 |
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60802126 |
May 22, 2006 |
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60907450 |
Apr 2, 2007 |
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60924203 |
May 3, 2007 |
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Current U.S.
Class: |
381/111 |
Current CPC
Class: |
H02K 7/10 20130101; H02K
33/16 20130101; B81B 3/0021 20130101; H02K 2201/18 20130101; H02N
13/00 20130101; H02K 16/00 20130101; H04R 1/403 20130101; H04R
1/005 20130101; H04R 1/20 20130101; H04R 3/12 20130101 |
Class at
Publication: |
381/111 |
International
Class: |
H04R 1/20 20060101
H04R001/20 |
Claims
1. Direct digital speaker apparatus receiving a digital input
signal and generating sound accordingly, the apparatus comprising:
an array of pressure-producing elements; and a controller operative
to compute a timing pattern determining if and when each
pressure-producing element is actuated so as to achieve a desired
directivity pattern; wherein said pressure-producing elements have
the same amplitude.
2. The direct digital speaker apparatus according to claim 1,
wherein the apparatus also comprises at least one latch operative
to selectively latch at least one subset of said pressure producing
elements in at least one latching position thereby; wherein said
controller comprises a latch controller operative to receive said
digital input signal and to control said at least one latch
accordingly.
3. The direct digital speaker apparatus according to claim 1,
configured to generate a plurality of directivity patterns, wherein
the controller is configured to compute the timing pattern so as to
achieve the desired directivity pattern which is selected out of
the plurality of directivity patterns which comprises at least
omnidirectional and uni-directional directivity patterns.
4. The direct digital speaker apparatus according to claim 1,
configured to generate a plurality of directivity patterns, wherein
the controller is configured to compute the timing pattern so as to
achieve the desired directivity pattern which is selected out of
the plurality of directivity patterns which comprises at least
omnidirectional, uni-directional and multidirectional directivity
patterns.
5. The direct digital speaker apparatus according to claim 1,
wherein the controller is operative to compute the timing pattern
so as to achieve the desired directivity pattern which corresponds
to propagation of sound outward from a given focal point.
6. The direct digital speaker apparatus according to claim 1,
wherein is sound produced by the pressure producing elements in
front of a surface of the pressure producing elements, wherein the
focal point is located at a distance d behind the surface of
pressure-producing elements.
7. The direct digital speaker apparatus according to claim 1,
wherein the controller is operative to compute the timing pattern
determining if and when each pressure-producing element is actuated
so as to achieve the desired directivity pattern in which different
propagation angles are used for the directivity pattern in
different planes.
8. The direct digital speaker apparatus according to claim 1,
wherein different subsets of one or more of the pressure-producing
elements have different propagation angles, wherein in a per-clock
operation of the controller the controller is operative to
determine how many moving elements should move during a current
clock based on the digital input signal and to determine which
moving elements should move during the current clock by selecting a
subset of pressure-producing element based on its matching to the
desired propagation angle.
9. The direct digital speaker apparatus according to claim 1,
wherein the desired directivity pattern is a cylindrical
pattern.
10. The direct digital speaker apparatus according to claim 1,
wherein the controller is operative to define at least one
attribute of the sound to correspond to at least one characteristic
of the digital input signal, thereby defining a highest frequency
for the sound, wherein each of the pressure-producing elements
defines a cross section which is perpendicular to a respective axis
along which the pressure-producing element is constrained to travel
alternately back and forth, wherein the largest dimension of each
of the cross-sections of the pressure-producing elements is smaller
than the wavelength of the highest frequency.
11. The direct digital speaker apparatus according to claim 1,
wherein the direct digital speaker is a Microelectromechanical
system (MEMS) speaker which is fabricated using MEMS manufacturing
techniques.
12. The direct digital speaker apparatus according to claim 1,
wherein the controller is operative to compute the timing pattern
so as to achieve the desired directivity pattern which comprises
unidirectional sound in at least two different directions so as to
serve listeners located at different positions.
13. The direct digital speaker apparatus according to claim 12,
configured to generate different sound streams be simultaneously
perceived by the listeners positioned at the different positions,
wherein the controller is operative to compute the timing pattern
so as to achieve a desired directivity pattern in which the
different sound streams are produced in the different
directions.
14. The direct digital speaker apparatus according to claim 1,
comprising a plurality of arrays of pressure-producing elements;
wherein the controller is operative to compute different timing
patterns for the different arrays, and to operate the plurality of
arrays simultaneously in accordance with the different timing
patterns, thereby to obtain the single desired directivity
pattern.
15. The direct digital speaker apparatus according to claim 14,
wherein each of the plurality of arrays is of the same order of
magnitude of the sound wave's length.
16. The direct digital speaker apparatus according to claim 1,
wherein each of the pressure-producing elements is operative to
produce both positive pressure pulses and negative pressure
pulses.
17. Direct digital speaker apparatus receiving a digital input
signal and generating sound accordingly, the apparatus comprising:
A plurality of arrays of pressure-producing elements; and a
controller operative to compute a timing pattern determining if and
when each pressure-producing element in the plurality of arrays is
actuated so as to achieve a desired directivity pattern; wherein in
each of the arrays the pressure-producing elements have the same
amplitude; wherein different arrays of the plurality of arrays have
different characteristics which includes at least one of different
clock frequencies, different pressure-producing element sizes and
different amplitudes.
18. The direct digital speaker apparatus according to claim 17,
wherein a size of each of the arrays is of the same order of
magnitude of the sound wave's length.
19. The direct digital speaker apparatus according to claim 17,
configured to generate a plurality of directivity patterns, wherein
the controller is configured to compute the timing pattern so as to
achieve the desired directivity pattern which is selected out of
the plurality of directivity patterns which comprises at least
omnidirectional, uni-directional and multidirectional directivity
patterns.
Description
REFERENCE TO CO-PENDING APPLICATIONS
[0001] This application in a continuation of U.S. patent
application Ser. No. 12/601,427 which is a national phase of PCT
patent application serial number IL2007/000618 filing date May 21,
2007, which in turn claims priority from: (a) U.S. provisional
application No. 60/802,126 filed 22 May 2006 and entitled "An
apparatus for generating pressure"; (b) from a U.S. provisional
application No. 60/907,450 filed 2 Apr. 2007 and entitled
"Apparatus for generating pressure and methods of manufacture
thereof"; and (c) from U.S. provisional application 60/924,203
filed 3 May 2007 and entitled "Apparatus and Methods for Generating
Pressure Waves".
FIELD OF THE INVENTION
[0002] The present invention relates generally to actuators and
specifically to speakers.
BACKGROUND OF THE INVENTION
[0003] The state of the art for actuators comprising an array of
micro actuators is believed to be represented by the following, all
of which are US patent documents unless otherwise indicated: [0004]
2002/0106093: The Abstract, FIGS. 1-42 and paragraphs 0009, 0023,
and 0028 show electromagnetic radiation, actuators and transducers
and electrostatic devices. [0005] U.S. Pat. No. 6,373,955: The
Abstract and column 4, line 34-column 5, line 55 show an array of
transducers. [0006] JP 2001016675: The Abstract shows an array of
acoustic output transducers. [0007] U.S. Pat. No. 6,963,654: The
Abstract, FIGS. 1-3, 7-9 and column 7, line 41-column 8, line 54
show the transducer operation based on an electromagnetic force.
[0008] U.S. Pat. No. 6,125,189: The Abstract; FIGS. 1-4 and column
4, line 1-column 5, line 46, show an electro-acoustic transducing
unit including electrostatic driving. [0009] WO 8400460: The
Abstract shows an electromagnetic-acoustic transducer having an
array of magnets. [0010] U.S. Pat. No. 4,337,379: The Abstract;
column 3, lines 28-40, and FIGS. 4, 9 show electromagnetic forces.
[0011] U.S. Pat. No. 4,515,997: The Abstract and column 4, lines
16-20, show volume level. [0012] U.S. Pat. No. 6,795,561: Column 7,
lines 18-20, shows an array of micro actuators. [0013] U.S. Pat.
No. 5,517,570: The Abstract shows mapping aural phenomena to
discrete, addressable sound pixels. [0014] JP 57185790: The
Abstract shows eliminating the need for a D/A converter, [0015] JP
51120710: The Abstract shows a digital speaker system which does
not require any D-A converter. [0016] JP 09266599: The Abstract
shows directly applying the digital signal to a speaker. [0017]
U.S. Pat. No. 6,959,096: The Abstract and column 4, lines 50-63
show a plurality of transducers arranged within an array.
[0018] Methods for manufacturing polymer magnets are described in
the following publications: [0019] Lagorce, L. K. and M. G. Allen,
"Magnetic and Mechanical Properties of Micro-machined Strontium
Ferrite/Polyimide Composites", IEEE Journal of
Micro-electromechanical Systems, 6(4), December 1997; and [0020]
Lagorce, L. K., Brand, O. and M. G. Allen, "Magnetic micro
actuators based on polymer magnets", IEEE Journal of
Micro-electromechanical Systems, 8(1), March 1999. [0021] U.S. Pat.
No. 4,337,379 to Nakaya describes a planar electrodynamics
electro-acoustic transducer including, in FIG. 4A, a coil-like
structure. [0022] U.S. Pat. No. 6,963,654 to Sotme et al describes
a diaphragm, flat-type acoustic transducer and flat-type diaphragm.
The Sotme system includes, in FIG. 7, a coil-like structure.
[0023] Semiconductor digital loudspeaker arrays are known, such as
those described in United States Patent document 20010048123, U.S.
Pat. No. 6,403,995 to David Thomas, assigned to Texas Instruments
and issued 11 Jun. 2002, U.S. Pat. No. 4,194,095 to Sony, U.S. Pat.
No. 4,515,997 to Walter Stinger, and Diamond Brett M., et al,
"Digital sound reconstruction using array of CMOS-MEMS
micro-speakers", Transducers '03, The 12.sup.th International
Conference on Solid State Sensors, Actuators and Microsystems,
Boston, Jun. 8-12, 2003; and such as BBE's DS48 Digital Loudspeaker
Management System.
[0024] YSP 1000 is an example of a phased array speaker
manufactured by Yamaha.
[0025] The disclosures of all publications and patent documents
mentioned in the specification, and of the publications and patent
documents cited therein directly or indirectly, are hereby
incorporated by reference.
SUMMARY OF THE INVENTION
[0026] Provided herewith, in accordance with certain embodiments of
the present invention, is direct digital speaker apparatus
receiving a digital input signal and generating sound accordingly,
the apparatus comprising an array of pressure-producing elements
such as but not limited to moving elements as described herein; and
a controller operative to compute a timing pattern determining if
and when each pressure-producing element is actuated so as to
achieve a desired directivity pattern.
[0027] Further in accordance with a preferred embodiment of the
present invention, at least one pressure-producing element is
capable of producing positive pressure pulses and at least one
pressure-producing element is capable of producing negative
pressure pulses.
[0028] Still further in accordance with a preferred embodiment of
the present invention, each pressure-producing element is operative
to produce both positive pressure pulses and negative pressure
pulses.
[0029] Also provided, in accordance with a preferred embodiment of
the present invention, is a method for controlling direct digital
speaker apparatus receiving a digital input signal and generating
sound accordingly, the method comprising providing an array of
pressure-producing elements, and computing a timing pattern
determining if and when each pressure-producing element is
operative to produce pressure pulses so as to achieve a desired
directivity pattern.
[0030] Further in accordance with a preferred embodiment of the
present invention, each pressure-producing element comprises a
moving element, operating to travel alternately back and forth
along a respective path
[0031] Still further in accordance with a preferred embodiment of
the present invention, the apparatus also comprises a user
interface receiving a desired directivity pattern from a user.
[0032] Further in accordance with a preferred embodiment of the
present invention, the directivity pattern is omni-directional
defining a focal point.
[0033] Still further in accordance with a preferred embodiment of
the present invention, the directivity pattern is cylindrical
defining a focal axis.
[0034] Further in accordance with a preferred embodiment of the
present invention, the directivity pattern is unidirectional
defining an angle of propagation.
[0035] Still further in accordance with a preferred embodiment of
the present invention, the directivity pattern comprises a
combination of a plurality of unidirectional directivity
patterns.
[0036] Further in accordance with a preferred embodiment of the
present invention, the array is centered at the focal point.
[0037] Still further in accordance with a preferred embodiment of
the present invention, the array is centered at a projection of the
focal point.
[0038] Further in accordance with a preferred embodiment of the
present invention, the array is oriented symmetrically relative to
the axis.
[0039] Still further in accordance with a preferred embodiment of
the present invention, the array is rectangular, defining four
sides thereof, and the four sides include two sides parallel to the
axis.
[0040] Additionally in accordance with a preferred embodiment of
the present invention, the timing pattern comprises employing a
suitable delay for at least some of the pressure-producing
elements, using the formula: delay=[d.sup.2+r.sup.2).sup.0.5-d]/c,
where r=distance between the projection of the focal point onto the
pressure-producing elements array and a given pressure-producing
element, d=the distance of the plane of the array of the
pressure-producing elements from the focal point of the
onmi-directional sound, and c=the speed of sound propagation
through the medium in which the speaker is operating.
[0041] Still further in accordance with a preferred embodiment of
the present invention, the timing pattern comprises employing a
suitable delay for at least some of the pressure-producing
elements, using the formula: delay=[(d.sup.2+r.sup.2).sup.0.5-d]/c,
where r=distance between the projection of the focal axis onto the
pressure-producing elements array and a given pressure-producing
element, c=the speed of sound through the medium in which the
speaker is operating, and d=the distance of the plane of the array
of pressure-producing elements from the focal axis.
[0042] Further in accordance with a preferred embodiment of the
present invention, the timing pattern comprises employing a
suitable delay for at least some of the pressure-producing
elements, using the formula: delay=x cos .alpha. where x=the
distance from the plane defined by the pressure-producing elements
array edge and a given pressure-producing element and .alpha.=the
angle between the direction of the uni-directional propagation and
the pressure-producing elements array plane.
[0043] Further in accordance with a preferred embodiment of the
present invention, each of the pressure-producing elements is
individually controlled.
[0044] Still further in accordance with a preferred embodiment of
the present invention, the pressure-producing elements are moving
elements, that produce pressure by virtue of their movement.
[0045] Still further in accordance with a preferred embodiment of
the present invention, each moving element is responsive to
alternating magnetic fields and wherein the apparatus also
comprises at least one latch operative to selectively latch at
least one subset of the moving elements in at least one latching
position thereby to prevent the individual moving elements from
responding to the electromagnetic force, and wherein the controller
comprises a magnetic field control system operative to receive the
clock and, accordingly, to control application of the
electromagnetic force to the array of moving elements; and a latch
controller operative to receive the digital input signal and to
control the at least one latch accordingly.
[0046] Further in accordance with a preferred embodiment of the
present invention, the method also comprises reading in a desired
directivity pattern provided by a user.
[0047] Regarding terminology used herein:
[0048] Array: This term is intended to include any set of moving
elements whose axes are preferably disposed in mutually parallel
orientation and flush with one another so as to define a surface
which may be planar or curved.
[0049] Above, Below: It is appreciated that the terms "above" and
"below" and the like are used herein assuming that, as illustrated
by way of example, the direction of motion of the moving elements
is up and down however this need not be the case and alternatively
the moving elements may move along any desired axis such as a
horizontal axis.
[0050] Actuator: This term is intended to include transducers and
other devices for inter-conversion of energy forms. When the term
transducers is used, this is merely by way of example and it is
intended to refer to all suitable actuators such as speakers,
including loudspeakers.
[0051] Actuator element: This term is intended to include any
"column" of components which, typically in conjunction with many
other such columns, forms an actuator, each column typically
including a moving element, a pair of latches or "latching
elements" therefor, each latching element including one or more
electrodes and insulative spacing material separating the moving
element from the
[0052] Coil: It is appreciated that the alternating electromagnetic
force applied to the array of moving elements in accordance with a
preferred embodiment of the present invention may be generated by
an alternating electric current oriented to produce a magnetic
field gradient which is co-linear to the desired axes of motion of
the moving elements. This electric current may comprise current
flowing through a suitably oriented conductive coil or conductive
element of any other suitable configuration. The term "coil" is
used throughout the present specification as an example however it
is appreciated that there is no intention to limit the invention
which is intended to include all apparatus for applying an
alternating electromagnetic force e.g. as described above. When
"coil" is used to indicate a conductor, it is appreciated that the
conductor may have any suitable configuration such as a circle or
other closed figure or substantial portion thereof and is not
intended to be limited to configurations having multiple turns.
[0053] Channels, also termed "holes" or "tunnels": These are
illustrated as being cylindrical merely by way of example, this
need not be the case.
[0054] Electrode: An electro-static latch. Includes either the
bottom or top electro-static latch which latches its corresponding
moving element by virtue of its being oppositely charged such that
each latch and its moving element constitute a pair of oppositely
charged electrodes.
[0055] Flexure: at least one flexible element on which an object is
mounted, imparting at least one degree of freedom of motion to that
object, for example, one or more flexible thin or small elements
peripheral to and typically integrally formed e.g. from a single
sheet of material, with a central portion on which another object
may or may not be mounted, thereby to impart at least one degree of
freedom of motion to the central portion and objects mounted
thereupon.
[0056] Latch, latching layer, latching mechanism: This term is
intended to include any device for selectively locking one or more
moving elements into a fixed position. Typically, "top" and
"bottom" latching layers are provided, which may be side by side
and need not be one atop the other, and each latching layer
includes one or many latching mechanisms which may or may not
correspond in number to the number of moving elements to be
latched. The term "latch pair" is a pair of latches for an
individual moving element e.g. including a top latch and a bottom
latch, which may be side by side and need not be one atop the
other.
[0057] Moving elements: These are intended to include any moving
elements each constrained to travel alternately back and forth
along an axis in response to an alternating electromagnetic force
applied thereto. Moving elements are also termed herein
"micro-speakers", "pixels", "micro-actuators", "membranes"
(individually or collectively) and "pistons".
[0058] Spacers, also termed "space maintainers": Include any
element or elements mechanically maintaining the respective
positions of the electrodes and moving elements
[0059] The term "direct digital speaker" is used herein to include
speakers that accept a digital signal and translate the signal into
sound waves without the use of a separate digital to analog
converter, Such speakers may sometime include an analog to digital
converter as to allow them to translate analog signals instead or
in addition to digital signals. Such speakers may include DDS
(Direct Digital Speakers), DDL (Direct Digital Loudspeakers), DSR
(Digital Sound Reconstruction) speakers, digital uniform
loudspeaker arrays, matrix speakers, and MEMS speakers. The term
"direct digital speaker" as used herein is intended to include
speaker apparatus having a multiplicity of pressure-producing
elements, which generate pressure either by virtue of their motion
e.g. as specifically described herein or by heating and cooling the
medium in which they reside, e.g. air, or by accelerating the
medium in which they reside e.g. by ionizing the medium and
providing a potential difference along an axis, or by operating as
valves to selectively tap reservoirs of medium e.g. air,
pressurized differently from the surrounding environment. The
number of operating pressure producing elements (i.e. elements
which are operating to generate pressure) is typically a
monotonically increasing function of, e.g. proportional to, the
intensity of the input signal, if analog, or to the digitally
encoded intensity of the input signal, if digital.
[0060] The term "clock" used herein refers to the time duration
associated with a single interval of the system clock.
[0061] The term "directivity pattern" as used herein refers to the
pattern of the spatial distribution of the acoustic energy
generated by speaker apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] Preferred embodiments of the present invention are
illustrated in the following drawings:
[0063] FIG. 1A is a simplified functional block diagram
illustration of actuator apparatus constructed and operative in
accordance with a preferred embodiment of the present
invention.
[0064] FIG. 1B is an isometric illustration of the array of moving
elements of FIG. 1A constructed and operative in accordance with a
preferred embodiment of the present invention in which each moving
element comprises a magnet and each is constrained to travel,
except when latched, alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array of moving elements.
[0065] FIGS. 1C-1G are simplified top view illustrations of latches
constructed and operative in accordance with five alternative
embodiments of the present invention which can serve as
alternatives to the latch specifically shown in FIG. 1B.
[0066] FIG. 2A shows the array of FIG. 1B in a first, bottom
extreme position responsive to an electromagnetic force applied
downward.
[0067] FIG. 2B shows the array of FIG. 1B in a second, top extreme
position responsive to an electromagnetic force applied upward.
[0068] FIG. 2C is similar to FIG. 2B except that one of the
individual moving magnets is not responding to the upward force
because that individual magnet is latched into its top extreme
position by a corresponding electric charge disposed above the
individual moving magnet and functioning as a top latch.
[0069] FIGS. 3A-3C are respective top, cross-sectional and
isometric views of a skewed array of moving elements each
constrained to travel alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array of moving elements by a coil wrapped around the
array.
[0070] FIG. 4A is an exploded view of an actuator device including
an array of moving elements each constrained to travel alternately
back and forth along a respective axis in response to an
alternating electromagnetic force applied to the array of moving
elements by a coil, and a latch, formed as a layer, operative to
selectively latch at least one subset of the moving elements in at
least one latching position thereby to prevent the individual
moving elements from responding to the electromagnetic force.
[0071] FIG. 4B is a simplified flowchart illustration of a
preferred actuation method operative in accordance with a preferred
embodiment of the present invention.
[0072] FIG. 5 is an isometric static view of the actuator device of
FIG. 4A constructed and operative in accordance with a preferred
embodiment of the present invention in which the array of moving
elements is formed of thin foil, each moving element being
constrained by integrally formed flexures surrounding it.
[0073] FIG. 6A is an exploded view of a portion of the actuator
device of FIG. 5.
[0074] FIGS. 6B and 6C are a perspective view illustration and an
exploded view, respectively, of an assembly of moving elements and
associated flexures, latches and spacer elements constructed and
operative in accordance with a preferred embodiment of the present
invention which reduces leakage of air through the flexures.
[0075] FIG. 6D is a cross-sectional view of the apparatus of FIGS.
6B-6C showing three moving elements in top extreme, bottom extreme
and intermediate positions respectively.
[0076] FIG. 6E is a legend for FIG. 6D.
[0077] FIG. 7A is a static partial top view illustration of the
moving element layer of FIGS. 5-6C.
[0078] FIG. 7B is a cross-sectional view of the moving element
layer of FIGS. 5-6 taken along the A-A axis shown in FIG. 7A.
[0079] FIG. 7C is a perspective view of the moving element layer of
FIGS. 5-7B wherein an individual moving element is shown moving
upward toward its top extreme position such that its flexures
extend upward out of the plane of the thin foil.
[0080] FIG. 7D is a perspective view of a moving element layer
constructed and operative in accordance with an alternative
embodiment of the present invention in which the disc-shaped
permanent magnets of the embodiment of FIGS. 5-7C are replaced by
ring-shaped permanent magnets.
[0081] FIG. 7E is a side view illustration of the
flexure-restrained central portion of an individual moving element
in the embodiment of FIG. 7D.
[0082] FIG. 8A is a control diagram illustrating control of the
latches and of the coil-induced electromagnetic force for a
particular example in which the moving elements are arranged in
groups that can each, selectively, be actuated collectively,
wherein each latch in the latching layer is associated with a
permanent magnet, and wherein the poles of all of the permanent
magnets in the latching layer are all identically disposed.
[0083] FIG. 8B is a flowchart illustrating a preferred method
whereby a latching controller may process an incoming input signal
and control moving elements' latches accordingly, in groups.
[0084] FIG. 8C is a simplified functional block diagram
illustration of a processor, such as the processor 802 of FIG. 8A,
which is useful in controlling substantially any of the actuator
devices with electrostatic latch mechanisms shown and described
herein.
[0085] FIG. 8D is a simplified flowchart illustration of a
preferred method for initializing the apparatus of FIGS. 1-8C.
[0086] FIG. 8E is a simplified isometric view illustration of an
assembled speaker system constructed and operative in accordance
with a preferred embodiment of the present invention.
[0087] FIG. 8F is a simplified flowchart illustration of a
preferred method of operation for generating a sound using
apparatus constructed and operative in accordance with an
embodiment of the present invention.
[0088] FIG. 9A is a graph summarizing certain, although typically
not all, of the forces brought to bear on moving elements in
accordance with a preferred embodiment of the present
invention.
[0089] FIG. 9B is a simplified pictorial illustration of a magnetic
field gradient inducing layer constructed and operative in
accordance with a preferred embodiment of the present
invention.
[0090] FIGS. 9C-9D illustrate the magnetic field gradient induction
function of the conductive layer of FIG. 9B.
[0091] FIG. 10A is a simplified top cross-sectional illustration of
a latching layer suitable for latching moving elements partitioned
into several groups characterized in that any number of moving
elements may be actuated by collectively actuating selected groups
from among the partitioned groups, each latch in the latching layer
being associated with a permanent magnet, wherein the poles of all
of the permanent magnets in the latching layer are all identically
disposed.
[0092] FIG. 10B is a simplified electronic diagram of an
alternative embodiment of the latch layer of FIGS. 1-10A in which
each latch is individually controlled by the latching controller 50
of FIG. 8C. It is appreciated that the latches are shown to be
annular however alternatively may have any other suitable
configuration as described herein. The layer of FIG. 10B comprises
a grid of vertical and horizontal wires defining junctions. A gate
such as a field-effect transistor is typically provided at each
junction. To open an individual gate thereby to charge the
corresponding latch, voltage is provided along the corresponding
vertical and horizontal wires.
[0093] FIG. 11A is a timing diagram showing a preferred control
scheme used by the latch controller in uni-directional speaker
applications wherein an input signal representing a desired sound
is received, and moving elements constructed and operative in
accordance with a preferred embodiment of the present invention are
controlled responsively, so as to obtain a sound pattern in which
the volume in front of the speaker is greater than in other areas,
each latch in the latching layer being associated with a permanent
magnet, and the poles of all of the permanent magnets in the
latching layer preferably all or substantially all being similarly
or identically disposed.
[0094] FIG. 11B is a schematic illustration of an example array of
moving elements to which the timing diagram of FIG. 11A
pertains.
[0095] FIG. 11C is a timing diagram showing a preferred control
scheme used by the latch controller in omni-directional speaker
applications wherein an input signal representing a desired sound
is received, and moving elements constructed and operative in
accordance with a preferred embodiment of the present invention are
controlled responsively, so as to obtain a sound pattern in which
the volume in front of the speaker is similar to the volume in all
other areas surrounding the speaker.
[0096] FIGS. 12A and 12B are respectively simplified top view and
cross-sectional view illustrations of the moving element layer in
accordance with an alternative embodiment in which half of the
permanent magnets are placed north pole upward and half north pole
downward.
[0097] FIG. 13 is a simplified top view illustration similar to
FIG. 10A except that half of the permanent magnets in the latching
layer are disposed north pole upward and the remaining half of the
permanent magnets in the latching layer are disposed north pole
downward.
[0098] FIG. 14 is a control diagram illustrating control of the
latches and of the coil-induced electromagnetic force for a
particular example in which the moving elements are arranged in
groups that can each, selectively, be actuated collectively,
similar to FIG. 8A except that half of the permanent magnets in the
latching layer are disposed north pole upward and the remaining
half of the permanent magnets in the latching layer are disposed
north pole downward.
[0099] FIG. 15A is a timing diagram showing a preferred control
scheme used by the latch controller in uni-directional speaker
applications, which is similar to the timing diagram of FIG. 11A
except that half of the permanent magnets in the latching layer are
disposed north pole upward and the remaining half of the permanent
magnets in the latching layer are disposed north pole downward.
[0100] FIG. 15B is a schematic illustration of an example array of
moving elements to which the timing diagram of FIG. 15A
pertains.
[0101] FIG. 15C is a graph showing changes in the number of moving
elements disposed in top and bottom extreme positions at different
times and as a function of the frequency of the input signal
received by the latching controller of FIG. 8C.
[0102] FIG. 16A illustrates a moving element layer which is an
alternative to the moving element layer shown in FIGS. 1A and 2A-2C
in which the layer is formed from a thin foil such that each moving
element comprises a central portion and surrounding portions.
[0103] FIG. 16B is still another alternative to the moving element
layer shown in FIGS. 1A and 2A-2C in which a sheet of flexible
material e.g. rubber capable of enabling motion i.e. there are
rigid discs under the magnet. the magnet might be the rigid element
but it might not be rigid enough.
[0104] FIG. 16C is an isometric view of a preferred embodiment of
the moving elements and surrounding flexures depicted in FIG. 7A-7E
or 16A in which flexures vary in thickness.
[0105] FIG. 16D is an isometric illustration of a cost effective
alternative to the apparatus of FIG. 16C in which flexures vary in
width.
[0106] FIG. 17 is a top cross-sectional view illustration of an
array of actuator elements similar to the array of FIG. 3A except
that whereas in FIG. 3A, consecutive rows of individual moving
elements or latches are respectively skewed so as to increase the
number of actuator elements that can be packed into a given area,
the rows in FIG. 17 are unskewed and typically comprise a
rectangular array.
[0107] FIG. 18 is an exploded view of an alternative embodiment of
an array of actuator elements in which the cross-section of each
actuator element is square rather than round.
[0108] FIG. 19 is an isometric array of actuators supported within
a support frame providing an active area which is the sum of the
active areas of the individual actuator arrays.
[0109] FIG. 20A is a simplified generally self-explanatory
functional block diagram illustration of a preferred system for
achieving a desired directivity pattern for a desired sound stream
using a direct digital speaker with characteristics as indicated in
the drawing, such as that shown and described herein in FIGS.
1A-19.
[0110] FIG. 20B is a simplified generally self-explanatory
functional block diagram illustration of a preferred system for
achieving a desired directivity pattern for a desired sound stream
which is of general applicability in that it need not employ a
direct digital speaker with characteristics as indicated in FIG.
20A e.g. that shown and described herein in FIGS. 1A-19 and may
instead employ any suitable direct digital speaker.
[0111] FIG. 21 is a simplified flowchart illustration of per-clock
operation of the moving element constraint controller 3050 of FIG.
20, in accordance with certain embodiments of the present
invention.
[0112] FIG. 22A is a simplified diagram of an omni-directional
propagation pattern.
[0113] FIG. 22B is a diagram of a preferred positioning of a moving
element array relative to the focal point of the desired
omni-directional sound propagation pattern of FIG. 22A.
[0114] FIG. 23 is a simplified pictorial illustration of speaker
apparatus constructed and operative in accordance with FIGS.
20A-22B and operative, e.g. by virtue of having been so programmed,
to generate omni-directional sound which is particularly suitable
for an environment in which consumers of the sound entirely
surround the speaker, typically at more than one levels including a
ground level and a first floor level as shown.
[0115] FIG. 24 is a diagram of a cylindrical pattern of sound
directivity which it is achievable using an embodiment of the
apparatus of the present invention.
[0116] FIG. 25 is a diagram showing one preferred positioning of
the moving element array 3010, shown to be rectangular by way of
example, relative to the cylindrical pattern of sound directivity
shown in FIG. 24.
[0117] FIG. 26 is an isometric view of the moving element array of
FIGS. 20A-20B, showing uni-directional sound generated by that
moving array and propagating in a desired or predetermined
direction a as indicated by arrows.
[0118] FIG. 27 is a pictorial illustration of a preferred
application for speaker apparatus 3600 constructed and operative in
accordance with the present invention, being constructed e.g.
programmed to generate uni-directional sound in at least one
typically user-selected direction.
[0119] FIG. 28 is a simplified pictorial illustration of a
non-rectangular array of moving elements constructed and operative
in accordance with a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0120] The technical field of the invention is that of a digital
transducer array of long-stroke electromechanical micro actuators
constructed using fabrication materials and techniques to produce
low cost devices for a wide variety of applications, such as audio
speakers, biomedical dispensing applications, medical and
industrial sensing systems, optical switching, light reflection for
display systems and any other application that requires or can
derive benefit from longer-travel actuation and/or the displacement
of greater volumes of fluid e.g. air or liquid relative to the
transducer size.
[0121] A preferred embodiment of the present invention seeks to
provide a transducer structure, a digital control mechanism and
various fabrication techniques to create transducer arrays with a
number, N, of micro actuators. The array is typically constructed
out of a structure of typically three primary layers which in
certain embodiments would comprise of a membrane layer fabricated
out of a material of particular low-fatigue properties that has
typically been layered on both sides with particular polar aligned
magnetic coatings and etched with a number, N, of unique
"serpentine like" shapes, so as to enable portions of the membrane
bidirectional linear freedom of movement (the actuator). The
bidirectional linear travel of each moving section of the membrane
is confined within a chamber (actuator channels) naturally formed
typically by sandwiching the membrane layer between two mirror
image support structures constructed out of dielectric, Silicon,
Polymer or any other like insulating substrate, are typically
fabricated with N precisely sized through holes equal in number to
the N serpentine etchings of the membrane and typically precisely
positioned in a pattern which precisely aligns each through hole
with each serpentine etching of the membrane. Further affixed to
the outer surfaces of both the top and bottom layers of the support
structure are, typically, conductive overhanging surfaces such as
conductive rings or discs ("addressable electrodes"), which serve
to attract and hold each actuator as it reaches its end of stroke
typically by applying electrostatic charge.
[0122] A device constructed and operative in accordance with a
preferred embodiment of the present invention is now described with
reference to FIGS. 1B, 2A-2C, 3A-3C, 4A, 5, 6A, 7A 7B, 8A 8B, 9,
10A, 11A, 12A, 13, 14, 15A, 16A-C, 17-19.
[0123] FIG. 1B is a conceptual overview of a small section of the
device. FIG. 2A depicts the movement of the moving elements under
magnetic field. FIG. 2B depicts the movement of the same moving
elements under an opposite magnetic field. FIG. 2C depicts the
movement of the moving elements under a magnetic field while one
electrode is charged. FIGS. 3A-3C are respective top,
cross-sectional and perspective views of one preferred embodiment
of the present invention.
[0124] FIG. 4A is an exploded view of a device constructed and
operative in accordance with a preferred embodiment of the present
invention. FIG. 5 is a detailed illustration of a small section of
the device constructed and operative in accordance with a preferred
embodiment of the present invention. FIG. 6A is an exploded view of
the same small section. FIG. 7A is a pictorial illustration of a
serpentine and moving elements subassembly constructed and
operative in accordance with a preferred embodiment of the present
invention. FIG. 7B is an illustrative view of a single element,
constructed and operative in accordance with a preferred embodiment
of the present invention, in motion. FIG. 8A is a block diagram of
a speaker system constructed and operative in accordance with a
preferred embodiment of the present invention. FIG. 8B is a flow
diagram of the speaker system constructed and operative in
accordance with a preferred embodiment of the present invention.
FIG. 9A illustrates a preferred relationship between the different
forces applied to the moving elements.
[0125] FIG. 10A is a grouping view of the electrodes constructed
and operative in accordance with a preferred embodiment of the
present invention. FIG. 11A is a timing and control chart
constructed and operative in accordance with a preferred embodiment
of the present invention. FIG. 12A illustrates magnetic properties
of moving elements for an alternative addressing embodiment. FIG.
13 illustrates grouping of electrodes in an alternative addressing
embodiment. FIG. 14 is a simplified block diagram of the speaker
system in an alternative addressing embodiment. FIG. 15A is a
timing and control chart for an alternative embodiment. FIG. 16A is
a small section of the moving elements subassembly constructed and
operative in accordance with a preferred embodiment of the present
invention. FIG. 16B is a small section of a different embodiment of
the moving elements subassembly, using a flexible substrate
constructed and operative in accordance with a preferred embodiment
of the present invention.
[0126] Whereas FIGS. 3A-3C above illustrate an array of elements in
a honeycomb construction constructed and operative in accordance
with a preferred embodiment of the present invention, FIG. 17
illustrates an array of elements in a square construction, which is
constructed and operative in accordance with a preferred embodiment
of the present invention. FIG. 18 is an exploded view of a small
section of an embodiment using square shaped elements. FIG. 19
illustrates an apparatus using a plurality (array) of devices.
[0127] Effective addressing is typically achieved through unique
patterns of interconnects between select electrodes and unique
signal processing algorithms which typically effectively segments
the total number of actuators in a single transducer, into N
addressable actuator groups of different sizes, beginning with a
group of one actuator followed by a group of double the number of
actuators of its previous group, until all N actuators in the
transducer have been so grouped.
[0128] To attain actuator strokes the transducer is typically
encompassed with a wire coil, which, when electrical current is
applied, creates an electromagnetic field across the entire
transducer. The electromagnetic field causes the moving part of the
membrane to move typically in a linear fashion through the actuator
channels. If the current alternates its polarity, it causes the
moving part of the membrane to vibrate. When electrostatic charge
is applied to particular addressable electrode groups, it will
typically cause all actuators in that group to lock at the end of
the stroke, either on top or bottom of the support structure in
accordance with the application requirement. Collectively the
displacement provided by the transducer is achieved from the sum
total of the N actuators that are not locked at any particular
interval (super position).
[0129] The transducer construction is typically fully scalable in
the number of actuators per transducer, the size of each actuator,
and the length of stroke of each actuator, and the number of
addressable actuator groups. In certain embodiments, the actuator
elements may be constructed by etching various shapes into a
particular material, or by using layered metallic disks that have
been coated with a flexible material or by using free floating
actuator elements The membrane (flexure) materials may include
Silicon, Beryllium Copper, Copper Tungsten alloys, Copper Titanium
alloys, stainless steel or any other low fatigue material. The
addressable electrodes of the support structure may be grouped in
any pattern as to attain addressing as appropriate for the
transducer application. The addressable electrodes may be affixed
such that contact is created with the membrane actuator or in such
a manner that there is no physical contact with the membrane. The
substrate material may be of any insulating material such as FR4,
silicon, ceramic or any variety of plastics. In some embodiments
the material may contain ferrite particles. The number of
serpentine shapes etched into the membrane, or floating actuator
elements and the corresponding channels of the support structure
may be round, square or any other shape. The electromagnetic field
may be created by winding a coil around the entire transducer,
around sections of the transducer or around each actuator element
or by placing one or more coils placed next to one or more actuator
elements.
[0130] In certain embodiments a direct digital method is used to
produce sound using an array of micro-speakers. Digital sound
reconstruction typically involves the summation of discrete
acoustic pulses of energy to produce sound-waves. These pulses may
be based on a digital signal coming from audio electronics or
digital media in which each signal bit controls a group of
micro-speakers. In one preferred embodiment of the current
invention, the nth bit of the incoming digital signal controls
2.sup.n micro-speakers in the array, where the most significant bit
(MSB) controls about half of the micro-speakers and the least
significant bit (LSB) controls at least a single micro-speaker.
When the signal for a particular bit is high, all of the speakers
in the group assigned to the bit are typically activated for that
sample interval. The number of speakers in the array and the pulse
frequency determine the resolution of the resulting sound-wave. In
a typical embodiment, the pulse frequency may be the
source-sampling rate. Through the post application of an acoustic
low-pass filter from the human ear or other source, the listener
typically hears an acoustically smoother signal identical to the
original analog waveform represented by the digital signal.
[0131] According to the sound reconstruction method described
herein, the generated sound pressure is proportional to the number
of operating speakers. Different frequencies are produced by
varying the number of speaker pulses over time. Unlike analog
speakers, individual micro-speakers typically operate in a
non-linear region to maximize dynamic range while still being able
to produce low frequency sounds. The net linearity of the array
typically results from linearity of the acoustic wave equation and
uniformity between individual speakers. The total number of
non-linear components in the generated sound wave is typically
inversely related to the number of micro-speakers in the
device.
[0132] In a preferred embodiment a digital transducer array is
employed to implement true, direct digital sound reconstruction.
The produced sound's dynamic range is proportional to the number of
micro-speakers in the array. The maximal sound pressure is
proportional to the stroke of each micro-speaker. It is therefore
desirable to generate long stroke transducers and to use as many as
possible. Several digital transducer array devices have been
developed over the years. One worth mentioning is a CMOS-MEMS
micro-speaker developed at Carnegie Mellon University. Using CMOS
fabrication process, they designed an 8-bit digital speaker chip
with 255 square micro-speakers, each micro-speaker 216 .mu.m on a
side. The membrane is composed of a serpentine Al--SiO2 mesh coated
with polymer and can be electrostatically actuated by applying a
varying electrical potential between the CMOS metal stack and
silicon substrate. The resulting out of plane motion is the source
of pressure waves that produce sound. Each membrane has a stroke of
about 10 .mu.m. Such short strokes are insufficient and the
generated sound levels are too soft for a loudspeaker. Another
issue is that the device requires a driving voltage of 40V. Such
voltage requires complex and expensive switching electronics.
Preferred embodiments of the device described herein overcome some
or all of these limitations and generate much louder sound levels
while eliminating the need for high switching voltages.
[0133] It is believed that the shape of each transducer has no
significant effect on the acoustic performance of the speaker.
Transducers may be packed in square, triangle or hexagonal grids,
inter alia.
[0134] The current invention typically makes use of a combination
of magnetic and electrostatic forces to allow a long stroke while
avoiding the problems associated with traditional magnetic or
electrostatic actuators.
[0135] The moving elements of the transducer array are typically
made to conduct electricity and may be magnetized so that the
magnetic poles are perpendicular to the transducer array surface.
Moderate conduction is sufficient. A coil surrounds the entire
transducer array or is placed next to each element and generates
the actuation force. Applying alternating current or alternating
current pulses to the coil creates an alternating magnetic field
gradient that forces all the moving elements to move up and down at
the same frequency as the alternating current. To control each
moving element, two electrodes may be employed, one above and one
below the moving elements.
[0136] The current applied to the coil typically drives the moving
elements into close proximity with the top and bottom electrode in
turn. A small electrostatic charge is applied to the moving
elements. Applying an opposite charge to one of the electrodes
generates an attracting force between the moving element and the
electrode. When the moving element is very close to the electrode,
the attracting force typically becomes larger than the force
generated by the coil magnetic field and the retracting spring and
the moving element is latched to the electrode. Removing the charge
or some of it from the electrode typically allows the moving
element to move along with all the other moving elements, under the
influence of the coil magnetic field and the flexures.
[0137] In accordance with certain embodiments, the actuator array
may be manufactured from 5 plates or layers: [0138] Top electrode
layer [0139] Top spacers (together shown as layer 402) [0140]
Moving elements 403 [0141] Bottom spacers [0142] Bottom electrode
layer (together shown as layer 404)
[0143] In accordance with certain embodiments, the array is
surrounded by a large coil 401. The diameter of this coil is
typically much larger than that of traditional coils used in prior
art magnetic actuators. The coil can be manufactured using
conventional production methods.
[0144] In certain embodiments the moving element is made of a
conductive and magnetic material. Moderate electrical conduction is
typically sufficient. The moving element may be manufactured using
many types of materials, including but not limited to rubber,
silicon, or metals and their alloys. If the material cannot be
magnetized or a stronger magnet is desired, a magnet may be
attached to it or it may be coated with magnetic material. This
coating is typically done by application, using a screen printing
process or other techniques known in the art, by epoxy or another
resin loaded with magnetic powder. In some embodiments, screen
printing can be performed using a resin mask created through a
photo-lithographic process. This layer is typically removed after
curing the resin/magnetic powder matrix. In certain embodiments the
epoxy or resin is cured while the device is subjected to a strong
magnetic field, orienting the powder particles in the resin matrix
to the desired direction. The geometry of the moving elements can
vary. In yet other embodiments, part of the moving elements may be
coated with the magnet and cured with a magnetic field oriented in
one direction while the rest are coated later and cured in an
opposite magnetic field causing the elements to move in opposite
directions under the same external magnetic field. In one preferred
embodiment, the moving element comprises a plate that has a
serpentine shape surrounding it, typically cut out from thin foil.
Alternatively, in certain embodiments it is possible to use a thick
material thinned only in the flexure area or by bonding relatively
thick plates to a thin layer patterned as flexures. This shape
allows part of the foil to move while the serpentine shape serves
as a compliant flexure. In certain other embodiments, the moving
part is a cylinder or a sphere, free to move about between the top
and bottom electrodes.
[0145] FIG. 1B, which illustrates a conceptual overview of small
section of the device in accordance with certain embodiments of the
invention, serves to provide a conception overview of the complete
transducer array structure. In the illustrated embodiment the
moving elements are pistons 101 which are typically magnetized so
that one pole 102 is on the top and the other 103 at the bottom of
each piston. A magnetic field generator (not shown) that typically
influences the entire transducer array structure creates a magnetic
field across the entire transducer array, typically causing pistons
101 to move up and down, thereby forcing the air out of the cavity
104. An electrostatic electrode typically resides on both the top
105 and bottom 106 of each cavity. The electrodes serve as latching
mechanisms that attract and hold each piston as it nears its end of
stroke typically preventing the piston from moving until the latch
is released, while allowing the pushed air to easily pass through.
In certain embodiments, the pistons 101 are made of an electrically
conductive material or coated with such material. At least one of
the elements, the piston and/or the electrostatic electrode is
typically covered by an dielectric layer to avoid shorting as
pull-down occurs.
[0146] FIGS. 2A-2C, taken together, illustrate the element movement
according to a preferred embodiment of the present invention. In
this embodiment a coil (not shown) typically surrounds the entire
transducer array structure, creating a magnetic field across the
entire transducer array which causes any magnetic element with
freedom of movement to travel according to the alternating
direction of the field. This causes the pistons to move typically
up and down.
[0147] In FIG. 2A the magnetic field 201 direction is downwards.
The magnetic field creates a force, driving the pistons 101 of the
entire array downwards.
[0148] In FIG. 2B the magnetic field 202 direction has changed and
is pointing upwards. The magnetic field creates a force, driving
the pistons 101 of the entire array upwards.
[0149] In FIG. 2C a positive electric charge is applied to one of
the top electrodes 205. The positive charge typically attracts the
electrons in the piston 204, causing the top of the piston 206 to
be negatively charged. The opposite charges 205 and 206 create an
attraction force which, when the gap is below a critical distance,
typically act to pull-down the two elements together. The magnetic
field 203 direction has changed again and is pointing downwards.
The piston 204 is typically held in place due to magnetic
attraction while the rest of the pistons are free to move, and move
to the bottom due to the influence of the magnetic field 203. In
this particular embodiment the charge applied to the electrode is
positive. Alternatively, a negative charge may be applied to the
electrodes, which will induct a negative charge to accumulate in
the near-side of the adjacent piston.
[0150] FIGS. 3A-3C show top, cross-sectional and perspective views
of one preferred embodiment.
[0151] In certain embodiments a coil 304 wrapped around the entire
transducer array generates an electromagnetic field across the
entire array structure, so that when current is applied, the
electromagnetic field causes the pistons 302 to move up 301 and
down 303.
[0152] FIG. 4A shows an exploded view of the device constructed and
operative in accordance with certain embodiments of the invention.
As shown, the exploded view of a transducer array structure reveals
that it comprises the following primary parts:
[0153] (a) A coil surrounding the entire transducer array 401
generates an electromagnetic field across the entire array
structure when voltage is applied to it. A preferred embodiment for
the coil is described herein with reference to FIGS. 9B-9D.
[0154] (b) In certain embodiments a top layer construction 402 may
comprise a spacer layer and electrode layer. In a certain
embodiment this layer may comprise a printed circuit board (herein
after "PCB") layer with an array of accurately spaced cavities each
typically having an electrode ring affixed at the top of each
cavity.
[0155] (c) The moving elements ("pistons") 403 in the current
embodiment may be comprised of a thin foil of conductive magnetized
material cut or etched with many very accurate plates typically
surrounded by "serpentine" shapes that serve as compliant flexures
that impart the foils with a specific measure of freedom of
movement.
[0156] (d) A bottom layer construction 404 may comprise a spacer
layer and electrode layer. In a certain embodiment this layer may
comprise a dielectric layer with an array of accurately spaced
cavities each typically having an electrode ring affixed at the
bottom of each cavity.
[0157] FIG. 5 shows details of a small section of a device
constructed and operative in accordance with a preferred embodiment
of the present invention. A cross section detailed dimensional view
of the transducer array according to the illustrated embodiment
shows the following structure: the moving elements ("pistons"),
typically made from a thin foil 501 that has been cut or etched
into precise plate and serpentine shapes having a magnetized layer
on the top 502 and bottom 503, is accurately positioned so the
center of each plate shape is precisely aligned with the center of
each of the cavities of a top layer dielectric 504 and the bottom
layer dielectric cavity 505 that collectively serve as travel
guides and air ducts. At the external edges of each duct both on
the top 506 and on the bottom 507 is a copper ring ("electrode")
latching mechanism which, when electrostatic charge is applied,
typically attracts each moving element to create contact between
the moving elements ("pistons") and latches and holds each moving
element ("piston") as it nears the end of each stroke, thereby
preventing the moving element ("piston") from moving until the
latch is released typically by terminating the electrostatic charge
to the electrode.
[0158] FIG. 6A shows an exploded view of the same small section as
shown in FIG. 5. and reveals that in this embodiment the thin foil
which has been etched with precise serpentine shapes to create a
moving element ("piston") with the center of each shape affixed
with a magnetized layer on the top and bottom, is centered and
enclosed in the cavities of mirror image on the top 602 and bottom
603 dielectric.
[0159] FIG. 7A shows a serpentine shape and moving elements
subassembly constructed and operative in accordance with a
preferred embodiment of the present invention. A top static view of
the thin foil shows the moving element in this embodiment is
typically constructed by etching a precise round serpentine shape
that allows the center of the shape 701 freedom of movement
restrained by the flexures of the shapes 703 which have been etched
out of the material, thereby to form interspersing cavities 702. A
cross sectional view reveals that the foil typically has polar
aligned layers of magnets, affixed to both the top 704 and the
bottom 705 of the tin foil moving element layer. As an alternative
to this embodiment, a layer of magnets may be affixed only to one
side of the thin foil.
[0160] FIG. 7B is an illustrative view of a single element in
motion, showing the upward freedom of movement of certain
embodiments where the magnetized center 706 of a single serpentine
shape is free to extend upward while being guided and restrained by
the serpentine etched flexures 707. Not shown in the illustration
is the opposite (downward) movement of the serpentine shape as it
travels in the opposite direction, and by doing so the flexures
extend downward.
[0161] In certain embodiments the top of each shape center 708 and
the bottom of each layer 709 are affixed magnetized layers that
have been aligned in the same magnetic polarity.
[0162] FIG. 8A shows a block diagram of the speaker system in
accordance with a preferred embodiment of the present invention. In
certain embodiments the digital input signal (common protocols are
I2S, I2C or SPDIF) 801 enters into a logic processor 802 which in
turn translates the signal to define the latching mechanism of each
grouping of moving elements. Group addressing is typically
separated into two primary groups, one for latching the moving
elements at the top, and one for latching the moving elements at
the bottom of their strokes. Each group is typically then further
separated into logical addressing groups typically starting with a
group of at least one moving element, followed by another group
that doubles the moving elements of the previous group, followed by
a another group which again doubles the number of elements of the
previous, and so on, until all moving elements of the entire array
have been grouped. The Nth group comprises 2.sup.N-1 moving
elements.
[0163] In the embodiment depicted in the block diagram of FIG. 8A,
the top group of one element group 803, a two element group 804 and
then a four element group 805 are shown and so on, until the total
numbers of moving elements in the transducer array assembly have
been addressed to receive a control signal from the processor
802.
[0164] The same grouping pattern is typically replicated for the
bottom latching mechanisms where a one element group 807 may be
followed by a two element group 808 and then a four element group
809 and so on, until the total numbers of moving elements in the
transducer array assembly have been addressed to receive a control
signal from the processor 802.
[0165] The processor 802 may also control an alternating current
flow to the coil that surrounds the entire transducer array 812,
thus creating and controlling the magnetic field across the entire
array. In certain embodiments a power amplifier 811 may be used to
boost current to the coil.
[0166] FIG. 8B illustrates a flow diagram of the speaker system. In
certain embodiments where the sampling rate of the digital input
signal 813 might be different from the device natural sampling
rate, the resampling module 814 may re-sample the signal, so that
it matches the device's sampling-rate. Otherwise, the resampling
module 814 passes the signal through as unmodified.
[0167] The scaling module 815 typically adds a bias level to the
signal and scales it, assuming the incoming signal 813 resolution
is M bits per sample, and the sample values X range between
-2.sup.(M-1) and 2.sup.(M-1)-1.
[0168] It is also assumed that in certain embodiments the speaker
array has N element groups (numbered 1 . . . N), as described in
FIG. 8A.
[0169] K is defined to be: K=N-M
[0170] Typically, if the input resolution is higher than the number
of groups in the speaker (M>N), K is negative and the input
signal is scaled down. If the input resolution is lower than the
number of groups in the speaker (M<N), K is positive and the
input signal is scaled up. If they are equal, the input signal is
not scaled, only biased. The output Y of the scaling module 815 may
be: Y=2.sup.K[X+2.sup.M-1]. The output Y is rounded to the nearest
integer. The value of Y now ranges between 0 and 2N-1.
[0171] The bits comprising the binary value of Y are inspected.
Each bit controls a different group of moving elements. The least
significant bit (bit1) controls the smallest group (group 1). The
next bit (bit2) controls a group twice as big (group 2). The next
bit (bit3) controls a group twice as big as group 2 etc. The most
significant bit (bitN) controls the largest group (group N). The
states of all the bits comprising Y are typically inspected
simultaneously by blocks 816, 823, . . . 824.
[0172] The bits are handled in a similar manner. Following is a
preferred algorithm for inspecting bit1:
[0173] Block 816 checks bit1 (least significant bit) of Y. If it is
high, it is compared to its previous state 817. If bit1 was high
previously, there is no need to change the position of the moving
elements in group 1. If it was low before this, the processor waits
for the magnetic field to point upwards, as indicated by reference
numeral 818 and then, as indicated by reference numeral 819, the
processor typically releases the bottom latching mechanism B1,
while engaging the top latching mechanism T1, allowing the moving
elements in group 1 to move from the bottom to the top of the
device.
[0174] If block 816 determines that bit1 of Y is low, it is
compared to its previous state 820. If bit1 was low previously,
there is no need to change the position of the moving elements in
group 1. If its previous state was high, the processor waits for
the magnetic field to point downwards, as indicated by reference
numeral 821 and then, as indicated by reference numeral 822, the
processor releases the top latching mechanism T1 while engaging the
top latching mechanism B1, allowing the moving elements in group 1
to move from the top to the bottom of the device.
[0175] FIG. 9A shows typical relationships between the different
major forces applied to moving elements. The different forces being
applied to the moving elements typically work in harmony to
counterbalance each other in order to achieve the desired function.
Forces toward the center are shown as negative forces, while forces
driving the element further away from the center (either toward the
up or down latching mechanisms) are shown as positive forces.
[0176] In the present embodiment the moving element is influenced
by 3 major forces:
[0177] a. Magnetic force, created by the interaction of the
magnetic field and the hard magnet. The direction of this force
depends on the polarity of the moving element magnet, the direction
of the magnetic field and the magnetic field gradient.
[0178] b. Electrostatic force, typically created by applying a
certain charge to the electrode and an opposite charge to the
moving element. The direction of this force is such as to attract
the moving element to the electrode (defined as positive in this
figure). This force increases significantly when the distance
between the moving element and the electrode becomes very small,
and/or where this gap comprises material with a high dielectric
constant.
[0179] c. Retracting force created by the flexures, (which act as
springs). The direction of this force is always towards the center
of the device (defined as negative in this figure). This force is
relatively small since the flexures are compliant, and is linear in
nature.
[0180] The relationship between the forces shows that typically, as
the moving element increasingly nears the end of its stroke, the
electrostatic force (generated by the latching mechanism)
increases, ultimately achieving sufficient force to attract and
latch the moving element. When the latch is released, the
retracting and magnetic forces are typically able to pull the
moving element away from the latch toward the center, thereby
inducing travel of the moving element. As the moving element
travels to the center, typically, the retracting force of the
flexure diminishes and ultimately is overcome, and is then
controlled by the electromagnetic force and the kinetic energy of
the moving element.
[0181] FIG. 10A shows a sectional view of the grouping pattern
applied in certain embodiments to the moving element ("pistons")
for purposes of digital addressing, as described previously in FIG.
8. In this embodiment there is a group of one element in the center
1001 followed by a two element group 1002, followed by a four
element group 1003, followed by a eight element group 1004,
followed by a 16 element group 1005, and so on.
[0182] As shown in this embodiment, to the extent possible each
increasing group has been arranged to extend around the previous
group, however this geometrical configuration can be altered in
order to accomplish different audio and/or constructive objectives.
For example moving the "epicenter" to the outer circumference of
the transducer array enables easier wire routing between each group
and the processor 802 (refer to FIGS. 8A-8B).
[0183] FIG. 11A shows a preferred timing and control chart. The
time chart describes preferred logic and algorithms for generating
a specific sound waveform. In the scope of this description, the
timeline is divided into slots, numbered I1, I2 and so on. This
simple example shows a device that uses 7 moving elements divided
into 3 groups. The first group comprises one moving element "P1"
and is controlled by the top latching mechanism "T1" and the bottom
latching mechanism "B1". The second group comprises two moving
elements "P2" and "P3" which are synchronized and move together.
This group is controlled by the top latching mechanism "T2" and the
bottom latching mechanism "B2". The second group comprises four
moving elements "P4", "P5", "P6" and "P7", which are synchronized
and move together. This group is controlled by the top latching
mechanism "T3" and the bottom latching mechanism "B3".
[0184] The "clock" chart at the top of the figure represents the
system clock. This clock is typically generated outside the device
and is transferred to the processor 802 (refer to FIG. 8) alongside
the sound signal. In a typical embodiment, the sampling rate of the
device is 44100 Hz. In such a case, the duration of each clock
interval is 24 .mu.sec and the clock changes its state every 11
.mu.sec.
[0185] The "signal" shown in this example is the analog waveform
that the device is generating. The "value" chart shows the digital
sample value of the signal at each clock interval. The "magnetic"
chart shows the direction (polarity) of the magnetic field
generated by the coil. The polarity changes synchronously with the
system clock.
[0186] This figure shows the state of each moving element using the
following display convention: An element ("P1" . . . "P7") that is
latched at the top 1101 is colored in black. An element that is
latched at the bottom 1102 is colored in white and an element that
is moving 1103 is hatched.
[0187] The digital sample value dictates how many elements may be
latched to the top and how many to the bottom of the array. In this
example, digital sample values of -3, -2, -1, 0, 1, 2, 3, and 4 are
possible. Each value is represented by 0, 1, 2, 3, 4, 5, 6 and 7
elements, respectively, latched to the top.
[0188] In time slice I1 the digital sample value is 0. This
requires 3 elements latched to the top and 4 to the bottom. The
magnetic field polarity is up. The top latching mechanisms T1 and
T2 are engaged and so is the bottom latching mechanism B3. At the
same time, the bottom latching mechanisms B1 and B2 are disengaged
and so is the top latching mechanism T3. Moving elements P1, P2 and
P3 are latched to the top while P4, P5, P6 and P7 are latched to
the bottom.
[0189] In time slice I3, the digital sample value changes to 1.
This requires 4 elements latched to the top and 3 to the bottom.
The magnetic field polarization is up. The bottom latch B3 is
disengaged, releasing elements P4, P5, P6 and P7 to move freely. At
the same time, the top latching mechanism T3 is engaged. The
elements move upwards under the influence of the magnetic field and
are latched by the currently engaged T3.
[0190] At this point, all 7 moving elements are latched to the top.
In the next slice I14, the moving elements P1, P2 and P3 would be
latched to the bottom, to ensure the device is in the desired state
(4 elements at the top and 3 at the bottom). In slice I4, the
polarity of the magnetic field changes and is directed downwards.
The top latching mechanisms T1 and T2 disengage and release the
moving elements P1, P2 and P3. At the same time, the bottom
latching mechanisms B1 and B2 are engaged and the approaching
moving elements P1, P2 and P3 are latched to the bottom position.
The moving elements P4, P5, P6 and P7 are held in place by the top
latching mechanism T3 and are therefore restrained from moving
downwards along with the other moving elements. The state of the
device at this point is: P1, P2 and P3 are latched to the bottom
and P4, P5, P6 and P7 are latched to the top. In time slices 15 to
14, the latching mechanisms are engaged and disengaged to allow the
moving elements to move and change their state according to the
digital sample values.
[0191] FIG. 12A shows preferred magnetic properties of moving
elements for addressing an alternative embodiment. A static top
view of the moving element foil shows one possible alternative
embodiment to the moving elements. In this embodiment two distinct
group segments of the moving elements 1201 and 1202 have been
created, enabling a single transducer array to process and generate
a louder signal, or alternatively two separate signals (such as the
left and right audio signal of stereo). The cross section view
shows that in order to accomplish the two groups of this embodiment
(discernible by the separated line 1203), each distinct group
segment typically has opposite magnetic polarity.
[0192] In one section group 1201 the layer of magnets affixed to
the moving element of the thin foil has been polarized so that
North (N) is on the top side of the foil 1204 and South (S) is on
the bottom side 1205; while in the second section group 1202 the
layer of magnets of the thin foil moving element have been
polarized so that South (S) is on the top side of the foil 1206 and
North (N) is on the bottom side 1207.
[0193] FIG. 13 shows grouping of electrodes in an alternative
embodiment. Similar to FIG. 10A, FIG. 13 depicts an alternative
addressing scheme for the alternative embodiment that is described
in FIG. 12A. In this case the grouping pattern applied to the
moving element for purposes of digital addressing is divided into
two primary group segments, half the transducer array in one
primary segment group, and the other half in another primary
segment group, as described in FIG. 12A.
[0194] In this embodiment there are two equal groups each with an
equal number of moving elements beginning with two groups 1301 and
1302 of one moving element each followed by two groups 1303 and
1304 with two elements in each group followed by two groupings 1305
and 1306 of four elements in each group, followed by two grouping
1307 and 1308 of eight elements in each group, followed by two
groupings 1309 and 1310 of sixteen elements in each group and so
on, until all moving elements of the transducer array have been
grouped and addressed.
[0195] As shown in the current embodiment, to the extent possible,
each increasing group has been arranged to extend around the
previous group, however this geometrical configuration can be
altered in order to accomplish different audio and/or constructive
objectives, for example moving the "epicenters" to the primary
groups to opposite sides of the outer circumference of the
transducer array enables easier wire routing between each group and
the processor 1402 (refer to FIG. 14). It also enables the device
to operate in two modes: monophonic, where both groups are used to
generate one to waveform at twice the amplitude, and stereophonic,
where each group generates a separate sound wave, as to allow
reconstruction of a stereophonic signal.
[0196] FIG. 14 shows a block diagram of the speaker system in an
alternative addressing embodiment. FIG. 14 describes addressing of
the alternative embodiment shown in FIGS. 12 and 13. The digital
input signal (I2S, I2C or SPDIF protocols) 1401 enters a logic
processor 1402 which in turn translates the signal to define the
latching mechanism of each the two primary grouping of moving
elements. Each addressing group is separated into two primary
groups, one for top and one for bottom latching mechanisms. Each
group is then further separated into logical addressing groups
starting with a group of one moving element, followed by another
group that doubles the moving elements of the previous group,
followed by a another group of double the number of elements of the
previous group, and so on, until all moving elements of the entire
array have been grouped.
[0197] In the embodiment depicted in the block diagram of FIG. 14,
the top stroke of one primary segments of moving elements begins
with a one element group 1403, and then a two element group 1404,
and then a four element group 1405, and so on, until the total
numbers of moving elements in the transducer array assembly have
been addressed to receive a control signal from the processor
1402.
[0198] The same grouping pattern is replicated for the down stroke
where a group of one element 1407 is followed by a two element
group 1408, and then a four element group 1409, and so on, until
the total numbers of moving elements in the transducer array
assembly have been addressed to receive a control signal from the
processor 1402.
[0199] This same pattern is replicated for the second primary
segment of moving elements with the top stroke group starting with
a one element group 1413, and then a two element group 1414, and
then a four element group 1415, and so on, until the total numbers
of moving elements in the transducer array assembly have been
addressed to receive a control signal from the processor 1402.
[0200] This is replicated for the down stroke of the second segment
beginning with a group of one element 1417, followed by a two
element group 1418, and then a four element group 1419, and so on,
until the total numbers of moving elements in the transducer array
assembly have been addressed to receive a control signal from the
processor 1402.
[0201] The processor 1402 will also control an alternating current
flow to the coil that typically surrounds the entire transducer
array, including both primary segments 1412, thus creating and
controlling the magnetic field across the entire array. In certain
embodiments a power amplifier 1411 may be used to boost current to
the coil.
[0202] FIG. 15A shows a timing and control chart for an alternative
embodiment. A time chart, describing the logic and algorithms, may
be used to generate a specific is sound waveform in the alternative
embodiment described in FIGS. 12 through 14. The display
conventions are similar to those used in FIG. 11A, and the same
signal is reproduced.
[0203] The timeline is divided into slots, numbered I1, I2 and so
on. This simple example shows a device that uses 14 moving elements
divided into two major groups (L and R), each divided into 3 minor
groups 1, 2 and 3.
[0204] The digital sample value dictates how many elements may be
latched to the top and how many to the bottom of the array. In this
example, digital sample values of -3, -2, -1, 0, 1, 2, 3, and 4 are
possible. Each value is represented by 0, 2, 4, 6, 8, 10, 12 and 14
elements, respectively, latched to the top.
[0205] On time slice I3, the digital sample value changes from 0 to
1. This requires 8 elements latched to the top and 6 to the bottom.
The magnetic field polarization is up. The top latches RT1 and RT2
as well as the bottom latch LB3 are disengaged, releasing elements
RP1, RP2, RP3, LP4, LP5, LP6 and LP7 to move freely. The magnetic
polarity of LP4, LP5, LP6 and LP7 creates an upwards force, driving
these elements upwards. The magnetic polarity of RP1, RP2 and RP3
is opposite and the driving force is downwards. At the same time,
the latching mechanisms opposite to the element movement are
engaged to grab the approaching moving elements and latch them in
place.
[0206] On slice I4, the polarity of the magnetic field changes and
is directed downwards. The top latches LT1 and LT2 as well as the
bottom latch RB3 are disengaged, releasing elements LP1, LP2, LP3,
RP4, RP5, RP6 and RP7 to move freely. The magnetic polarity of RP4,
RP5, RP6 and RP7 creates an upwards force, driving these elements
upwards. The magnetic polarity of LP1, LP2 and LP3 is opposite and
the driving force is downwards. At the same time, the latching
mechanisms opposite to the element movement are engaged to grab the
approaching moving elements and latch them in place.
[0207] On time slices I5 to I14, the latching mechanisms are
engaged and disengaged to allow the moving elements to move and
change their state according to the digital sample values.
[0208] FIG. 15C illustrates production of three different pitches
(22 KHz, 11 KHz and 4.4 KHz) of sound graphs II-IV respectively.
Graph I shows the system clock which, in the illustrated example is
44 KHz. In the illustrated embodiment, the speaker used to generate
these pitches has 2047 moving elements. When the 22 KHz sound (half
of the clock) is generated, all 2047 elements change position (from
top to bottom or vice versa) at each clock. When the 11 KHz
(quarter of the clock) sound is generated, half of the 2047 moving
elements change position at each clock. For example, if in the
first clock all 2047 moving elements are in their top position, in
the second clock, 1023 of these are lowered, in the third clock the
remaining 1024 elements are lowered, in the fourth clock 1023 are
raised, in the fifth clock the remaining 1024 elements are raised,
and so forth. When the 4.4 KHz ( 1/10 of the clock) sound is
generated, the numbers of elements which are in their top position
at each clock (1340, 1852, . . . ) are shown on top of Graph TV
whereas the numbers of elements which are in their bottom position
at each clock (707, 195, . . . ) are shown on the bottom of Graph
IV.
[0209] FIG. 16A shows a small section of the moving elements
subassembly.
[0210] FIGS. 16A and 16B provide illustrated views of the moving
elements in different embodiments.
[0211] The embodiment shown in FIG. 16A is of moving elements
("Pistons") constructed from a thin foil material 1601 with a
precise round serpentine shape etched into the material which
enables the center of the shape 1602 freedom of movement that is
restrained by the flexures of the shape.
[0212] FIG. 16B shows a small section of a different embodiment of
the moving elements subassembly, using a flexible substrate. This
embodiment is of moving elements ("pistons") constructed from a
material with sufficient elasticity, such as rubber polyethylene
material 1603, which either has magnetic material deposits in
specific shapes and dimensions on the top and bottom of the
material surface, or the material is affixed to a magnetized disk
of particular dimensions 1604, enabling freedom of movement that is
restrained by the material itself.
[0213] FIG. 2C shows a small section of a different embodiment of
the moving elements subassembly, using free-floating components.
This embodiment is of free floating moving elements ("pistons")
constructed from magnetized material with polar opposites at each
end. In this particular embodiment North is on top and South on the
bottom.
[0214] FIG. 3B illustrates a top view of a complete transducer
array structure in certain embodiments, based on a honeycomb
design, which enables a fill factor of 48 percent of the surface
area. FIG. 17 illustrates a top view of a completed transducer
array structure in certain embodiments, based on a square design,
which enables a fill factor of 38 percent of the surface area.
[0215] FIG. 18 shows an exploded view of a small section of an
embodiment using square shaped elements. This embodiment shows a
transducer array structure that utilizes square shape elements
intended to increase the fill factor and allow higher sound
pressure levels per transducer area.
[0216] As in previous embodiments, the same structural elements are
used. A coil surrounds the entire transducer array (not shown).
When voltage is applied, the coil generates an electromagnetic
actuation force across the entire array structure.
[0217] A top layer construction, typically comprising a dielectric
layer with an array of accurately spaced cavities 1802, each having
an electrode ring, is affixed at the top of each cavity, to create
an electrostatic latching mechanism 1801.
[0218] The moving elements ("pistons") in this embodiment comprises
a thin foil of conductive magnetized material cut or etched with
many very accurate "serpentine" shapes, that imparts the foils a
specific measure of freedom of movement 1803 with a magnetized top
1804 and bottom 1805. Each moving element is guided and restrained
by four flexures.
[0219] A bottom layer construction, typically comprising a
dielectric layer with an array of accurately spaced cavities 1806,
each having an electrode ring affixed at the bottom of each cavity,
creates an electrostatic latching mechanism 1807.
[0220] FIG. 19 shows an apparatus including a plurality (array) of
devices. The structure shows the use of plurality in certain
embodiments of array transducers 1902 as to create a device 1901
capable of generating louder sound pressure levels or use
beam-forming techniques (which extend beyond the scope of this
invention) to create directional sound waves.
[0221] The array may have any desired shape, and the round shapes
in the description are only for illustrative purposes.
[0222] The device constructed and operative in accordance with one
embodiment of the present invention and described above with
reference to FIGS. 1B, 2A-2C, 3A-3C, 4A, 5, 6A, 7A-7B, 8A-8B, 9A,
10A, 11A, 12A, 13, 14, 15A, 16A C, 17-19 is now described both more
generally, e.g. with reference to FIG. 1A, and in further detail.
Alternative embodiments are also described.
[0223] Reference is now made to FIG. 1A which is a simplified
functional block diagram illustration of actuator apparatus for
generating a physical effect, at least one attribute of which
corresponds to at least one characteristic of a digital input
signal sampled periodically in accordance with a clock. According
to a preferred embodiment of the present invention, the apparatus
of FIG. 1A comprises at least one actuator device, each actuating
device including an array 10 of moving elements each typically
constrained to travel alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array 10 of moving elements. Each moving element is constructed
and operative to be responsive to electromagnetic force. Each
moving element may therefore comprise a conductor, may be formed of
a ferro magnetic material, may comprise a permanent magnet e.g. as
shown in FIG. 6C, and may comprise a current-bearing coil.
[0224] A latch 20 is operative to selectively latch at least one
subset of the moving elements 10 in at least one latching position
thereby to prevent the individual moving elements 10 from
responding to the electromagnetic force. An electromagnetic field
controller 30 is operative to receive the clock and, accordingly,
to control application of the electromagnetic force by a magnetic
field generator, 40, to the array of moving elements. A latch
controller 50 is operative to receive the digital input signal and
to control the latch accordingly. The latch controller 50, in at
least one mode of latch control operation, is operative to set the
number of moving elements 10 which oscillate freely responsive to
the electromagnetic force applied by the magnetic field generator,
e.g. coil 40 to be substantially proportional to the intensity of
the sound, coded into the digital input signal it receives.
Preferably, when the intensity of sound coded into the digital
input signal is at a positive local maximum, all moving elements
are latched into a first extreme position. When the intensity of
sound coded into the digital input signal is at a negative local
maximum, all moving elements are latched into a second, opposing,
extreme position.
[0225] Preferably, a physical effect, e.g. sound, resembling the
input signal is achieved by matching the number of moving elements
in an extreme position e.g. a top position as described herein, to
the digital sample value, typically after resampling and scaling as
described in detail below. For example, if the digital sample value
is currently 10, 10 moving elements termed herein ME1, ME10 may be
in their top positions. If the digital sample value then changes to
13, three additional moving elements termed herein ME11, ME12 and
ME13 may be raised to their top position to reflect this. If the
next sample value is still 13, no moving elements need be put into
motion to reflect this. If the digital sample value then changes to
16, 3 different moving elements (since ME11, ME12 and ME13 are
already in their top positions), termed herein M14, M15 and M16,
may be raised to their top positions to reflect this.
[0226] In some embodiments, as described in detail below, moving
elements are constructed and operative to be operated collectively
in groups, such as a set of groups whose number of moving elements
are all sequential powers of two, such as 31 moving elements
constructed to be operated in groups having 1, 2, 4, 8, 16 moving
elements, respectively, each. In this case, and using the above
example, when the sample value is, say, 10, the two groups
including 8 and 2 moving elements respectively are both, say, up
i.e. all moving elements in them are in their top positions. When
the sample value changes to 13, however, it is typically
impractical to directly shift 3 moving elements from their bottom
positions to their top positions since in this example, due to the
binary grouping, this can only be done by raising the two groups
including 1 and 2 moving elements respectively, however, the group
including 2 moving elements is already raised. But the number of
top pixels may be otherwise matched to the sample value, 13: Since
13 8+4+1, the two groups including 4 and 1 pixels may be raised,
and the group including 2 pixels may be lowered, generating a net
pressure change of +3, thereby to generate a sound resembling the
input signal as desired, typically after re-sampling and
scaling.
[0227] More generally, moving elements translated toward a first
extreme position such as upward generate pressure in a first
direction termed herein positive pressure. Moving elements
translated toward the opposite extreme position such as downward
generate pressure in the opposite direction termed herein negative
pressure. A certain amount of positive or negative pressure may be
obtained either by translating the appropriate number of moving
elements in the corresponding direction, or by translating n moving
elements in the corresponding direction and others, m in number, in
the opposite direction, such that the difference n-m corresponds to
e.g. equals the sampled signal value, typically after re-sampling
and scaling.
[0228] The moving elements are typically formed of a material which
is at least moderately electrically conductive such as silicon or
silicon coated by a metal such as gold.
[0229] If the moving elements comprise permanent magnets, the
permanent magnets are typically magnetized during production such
that the magnetic poles are co-linear to the desired axes of
motion. A coil that typically surrounds the entire transducer array
generates the actuation force. To control each moving element, two
latch elements (typically comprising electro static latches or
"electrodes") are typically used, e.g. one above and one below the
moving elements.
[0230] According to one embodiment, the actuator is a speaker and
the array of moving elements 10 is disposed within a fluid medium.
The controllers 30 and 50 are then operative to define at least one
attribute of the sound to correspond to at least one characteristic
of the digital input signal. The sound has at least one wavelength
thereby to define a shortest wavelength present in the sound and
each moving element 10 typically defines a cross section which is
perpendicular to the moving element's axis and which defines a
largest dimension thereof, the largest dimension of each
cross-section typically being small relative to, e.g. an order of
magnitude smaller than, the shortest wavelength. FIG. 1B is an
isometric illustration of the array 10 of moving elements
constructed and operative in accordance with a preferred embodiment
of the present invention. In this embodiment, each moving element
10 comprises a magnet and each is constrained to travel, except
when and if latched, alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array of moving elements 10 by the magnetic field generator
40.
[0231] FIGS. 1C-1G are simplified top view illustrations of latch
elements 72, 73, 74, 76, and 77, any of which may, in combination
with similar or dissimilar others form the electrostatic latch 20
in accordance with alternative embodiments of the present
invention. At least one of the latch elements, 72, may have a
perforated configuration, as shown in FIG. 1C. In FIG. 1D, a latch
element 73 is shown having a notched configuration as to allow
concentration of electrostatic charge at the sharp portions of the
latch thereby to increase the latching force applied to the
corresponding moving element. In FIG. 1E, at least one latch
element, 74, has a configuration which includes a central area 75
which prevents air from passing so as to retard escape of air,
thereby to cushion contact between the moving element 10 and the
latching element itself. At least one latch element, 76, may have a
ring configuration, as shown in FIG. 1F and, by way of example, in
FIG. 1B. Latch element 77 of FIG. 1G is still another alternative
embodiment which is similar to latch element 74 of FIG. 1E except
that at least one radial groove 78 is provided so as to eliminate
induced current in the latch.
[0232] FIG. 2A shows the array of FIG. 1B in a first, bottom
extreme position responsive to an electromagnetic force applied, by
coil or other magnetic field generator 40 of FIG. 1A, downward.
FIG. 2B shows the array of FIG. 1B in a second, top extreme
position responsive to an electromagnetic force applied, by coil or
other magnetic field generator 40 of FIG. 1A, upward. FIG. 2C is
similar to FIG. 2B except that one of the individual moving
magnets, 204, is not responding to the upward force applied by
magnetic field generator 40 because that individual magnet is
latched into its top extreme position by a corresponding electric
charge disposed above the individual moving element and functioning
as a top latch. It is appreciated that in the embodiment of FIGS.
1A-2C, the latch 20 comprises an electrostatic latch, however this
need not be the case.
[0233] Typically, the apparatus of FIGS. 2A-2C comprises a pair of
latch elements 205 and 207 for each moving element, termed herein
"top" and "bottom" latch elements for simplicity although one need
not be above the other, the latch elements including one or more
electrodes and a space maintainer 220 separating the electrodes. In
embodiments in which the latch 20 comprises an electrostatic latch,
the space maintainer 220 may be formed of an insulating
material.
[0234] Each pair of latching elements is operative to selectively
latch its individual moving element 10 in a selectable one of two
latching positions, termed herein the first and second latching
positions or, for simplicity the "top" and "bottom" latching
positions, thereby to prevent the individual moving elements from
responding to the electromagnetic force. If the axis along which
each moving element 10 moves is regarded as comprising a first
half-axis and a second co-linear half-axis, the first latching
position is typically disposed within the first half-axis and the
second latching position is typically disposed within the second
half-axis as shown e.g. in FIGS. 2A-2C.
[0235] FIGS. 3A-3C are respective top, cross-sectional and
isometric views of a skewed array of moving elements 10 each
constrained to travel alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array of moving elements 10 e.g. by a coil 40 wrapped around
the array as shown. FIG. 4A is an exploded view of a layered
actuator device including an array of moving elements 403 each
constrained to travel alternately back and forth along a respective
axis in response to an alternating electromagnetic force applied to
the array of moving elements 403 by a coil 401, and a latch, formed
as at least one layer, operative to selectively latch at least one
subset of the moving elements 403 in at least one latching position
thereby to prevent the individual moving elements 403 from
responding to the electromagnetic force. Typically, the
electromagnetic force is generated using a coil 401 that surrounds
the array 403 as shown.
[0236] The latch typically comprises a pair of layers: a top latch
layer 402 and bottom latch layer 404 which, when charged, and when
the moving elements are in an appropriate electromagnetic field as
described herein, latch the moving elements into top and bottom
extreme positions respectively. Each of the latch layers 402 and
404 typically comprises an electrode layer and spacer layer as
shown in detail in FIGS. 5-6A. The spacer layers 402 and 404 may
generally be formed from any suitable dielectric material.
Optionally, ferrite or ferro-magnetic particles may be added to the
dielectric material to decrease undesirable interaction between the
magnets in the magnet layer.
[0237] In FIGS. 5-6A, both flexures and annular magnets or
conductors or ferromagnets are provided, however it is appreciated
that this is not intended to be limiting. Alternatively, for
example, other shaped magnets may be provided, or the annular
elements may be replaced by coils, and free-floating moving
elements may be provided without flexures, or the moving elements
may have a peripheral elastic or flexible portion or be associated
with a peripheral elastic or flexible member, all as shown and
described in detail herein.
[0238] FIG. 4B is a simplified flowchart illustration of a
preferred actuation method operative in accordance with a preferred
embodiment of the present invention. In FIG. 4B, a physical effect
is generated, at least one attribute of which corresponds to at
least one characteristic of a digital input signal sampled
periodically in accordance with a system clock signal. As shown,
the method typically comprises (step 450) providing at least one
array of moving elements 10 each constrained to travel alternately
back and forth along an axis 15 (FIG. 1B) in response to an
alternating electromagnetic force applied to the array of moving
elements 10 e.g. by magnetic field generator 40, In step 460, at
least one subset of the moving elements 10 is selectively latched
in at least one latching position by a latch 20 thereby to prevent
the individual moving elements 10 from responding to the
electromagnetic force applied by magnetic field generator 40. In
step 470, the system clock signal is received and, accordingly,
application of the electromagnetic force to the array of moving
elements is controlled. In step 480, the digital input signal is
received, and the latching step 460 is controlled accordingly.
Typically, as described above, the latch 20 comprises a pair of
layers, each layer comprising an array of electrostatic latch
elements and at least one space maintainer layer separates the
electrostatic latch layers and is formed of an insulating material.
Typically, the latch and at least one space maintainer are
manufactured using PCB production technology (FIG. 4B, step 450).
The array of moving elements typically comprises a magnetic layer
403 sandwiched between a pair of electrode layers spaced from the
magnetic layer by a pair of dielectric spacer layers. Typically, at
least one of the layers is manufactured using wafer bonding
technology, layer laminating technology, and/or PCB production
technology and/or combination of these technologies (FIG. 4B, step
455).
[0239] FIG. 5 is an isometric static view of the actuator device of
FIG. 4A constructed and operative in accordance with a preferred
embodiment of the present invention in which the array of moving
elements 10 is formed of thin foil, each moving element being
constrained by integrally formed flexures 606 surrounding it. The
flexures typically include foil portions 703 interspersed with
cut-out portions 702. FIG. 6A is an exploded view of a portion of
the actuator device of FIG. 5.
[0240] According to a preferred embodiment of the present
invention, 3 flexures are provided since at least three flexures
are required to define a plane. In the case of the moving elements
shown and described herein, the plane defined by the flexures is
typically a plane perpendicular to the desired axes of motion of
the moving elements or any plane suitably selected to constrain the
moving elements to travel along the desired axes.
[0241] Generally, it is desired to minimize the area of the
flexures so as to exploit the available area of the device for the
moving elements themselves since the process of actuation is
performed by the moving elements such that, from the point of view
of the functionality of the device, the area of the flexures is
overhead. For example, if the actuator is a speaker, the moving
elements push air thereby to create sound whereas the flexures and
the gaps defining them do not. Therefore, it is generally desirable
that the total length of the flexures be similar to the perimeter
of the moving elements (e.g. as opposed to being double the
perimeter of the moving elements). Therefore, it may be desired to
treat the total length of the flexures as given and consequently,
the more flexures provided, the shorter each flexure which
translates into higher stress under the same translation i.e, to
achieve the same amplitude of motion of the moving elements.
[0242] As a result, it is believed to be preferable to provide only
three flexures i.e. no more than the minimum number of flexures
required to securely hold the moving element, e.g. to define a
plane normal to the axis of motion of the moving elements.
[0243] FIGS. 6B and 6C are isometric and exploded view
illustrations, respectively, of an assembly of moving elements,
latches and spacer elements constructed and operative in accordance
with a preferred, low air leakage, embodiment of the present
invention. Air leakage refers to air passing from the space above
the moving element to the space below the moving element or vice
versa.
[0244] FIG. 6D is a cross-sectional view of the apparatus of FIGS.
6B-6C showing three moving elements 10 in top extreme, bottom
extreme and intermediate positions 610, 620 and 630 respectively.
FIG. 6E is a legend for FIG. 6D. Typically, in the embodiment of
FIGS. 6B-6E, at least one of the moving elements is configured to
prevent leakage of air through the at least one flexure. As shown,
at least one space maintainer 640 is disposed between the array of
moving elements 10 and the latching mechanism 20, the space
maintainer defining a cylinder 660 having a cross section, and
wherein at least one of the moving elements 10 comprises an
elongate element 670 whose cross-section is small enough to avoid
the flexures and a head element 680 mounted thereupon whose
cross-section is similar to the cross-section of the cylinder 660.
It is appreciated that for simplicity, only a portion of flexures
606 are shown.
[0245] FIG. 7A is a static partial top view illustration of the
moving element layer of FIGS. 5-6C. FIG. 7B is a cross-sectional
view of the moving element layer of FIGS. 5-6 taken along the A-A
axis shown in FIG. 7A. FIG. 7C is a perspective view of the moving
element layer of FIGS. 5-7B wherein an individual moving element is
shown moving upward toward its top extreme position such that its
flexures bend and extend upward out of the plane of the thin foil.
As shown, in FIGS. 7A-7C, at least one of the moving elements 10 of
FIG. 1A has a cross section defining a periphery 706 and is
restrained by at least one flexure attached to the periphery.
Typically, at least one moving element 10 and its restraining
typically serpentine flexures are formed from a single sheet of
material. Alternatively, as shown in FIG. 16B, at least one flexure
1605 may be formed of an elastic material. It is appreciated that
the flexure-based embodiment is only one possible embodiment of the
present invention. In contrast, as shown e.g. in FIG. 1B, each
moving element may simply comprise a free floating element.
[0246] FIG. 7D is a perspective view of a moving element layer
constructed and operative in accordance with an alternative
embodiment of the present invention. FIG. 7E is a side view
illustration of the flexure-restrained central portion 705 of an
individual moving element. In the embodiment of FIGS. 7D-7E, the
moving elements 10 of FIG. 1A comprise typically annular permanent
magnets 710 rather than the disc-shaped permanent magnets 502 of
the embodiments of FIGS. 5-7C. Typically, each moving element 10
has first and second opposing typically circular surfaces 711 and
712 facing first and second endpoints 713 and 714 of the moving
element's axis 715 of motion respectively and at least one
permanent magnet 710 is disposed on at least one of the first and
second circular surfaces 711 and 712. If two permanent magnets 710
are provided, then the two are aligned such that the same pole
points in the same direction as shown in FIG. 7E.
[0247] FIG. 8A is a control diagram illustrating control of latch
20 by latch controller 50 of FIG. 1A, and of the typically
coil-induced electromagnetic force, by controller 30 of FIG. 1A,
for a particular example in which the moving elements 10 are
arranged in groups G1, G2, . . . GN that can each, selectably, be
actuated collectively, wherein each latch in the latching layer is
typically associated with a permanent magnet, and wherein the poles
of all of the permanent magnets in the latching layer are all
identically disposed. The latch typically comprises, for each group
or each moving element in each group, a top latch and a bottom
latch. The top and bottom latches for group Gk (k=1, . . . N) are
termed Tk and Bk respectively. In FIG. 8A the two controllers are
both implemented in processor 802.
[0248] FIG. 8B is a flowchart illustrating a preferred method
whereby latching controller 50 of FIG. 1A may process an incoming
input signal 801 and control latches 20 of moving elements 10
accordingly, in groups. The abbreviation "EM" indicates
electromagnetic force applied upward or downward, depending on the
direction of the associated arrow, to a relevant group of moving
elements. In the embodiment illustrated in FIG. 8B, if at time t,
the LSB of the re-scaled PCM signal is 1 (step 816), this indicates
that the speaker elements in group G1 may be in the selected
end-position. If (step 817) group G1 is already in the selected
end-position, no further action is required, however if the group
G1 is not yet in the selected end-position, the latching controller
50 waits (step 818) for the electromagnetic field to be upward and
then (step 819) releases the bottom latches in set B1 and engages
the top latches in set T1. This is also the case, mutatis mutandis,
for all other groups G2, . . . GN.
[0249] In FIG. 8B, the notation Tk or Bk followed by an upward
pointing or downward pointing arrow indicates latching or releasing
(upward or downward arrow respectively) of the top or bottom (T or
B respectively) latch of the k'th group of moving elements.
[0250] FIG. 8C is a simplified functional block diagram
illustration of a processor, such as the processor 802 of FIG. 8A,
which is useful in controlling substantially any of the actuator
devices with electro-static latch mechanisms shown and described
herein. A single processor, in the embodiment of FIG. 8C,
implements both electromagnetic field controller 30 and latch
controller 50. The electromagnetic field controller 30 typically
receives the system clock 805 which is typically a square wave and
generates a sine wave with the same frequency and phase, providing
this to the coil 40 as an actuating signal. The DSP 810 may for
example comprise a suitably programmed TI 6000 digital signal
processor commercially available from Texas Instruments. The
program for the DSP 810 may reside in a suitable memory chip 820
such as a flash memory. The latch controller 50, in at least one
mode of latch control operation, is operative to set the number of
moving elements which oscillate freely responsive to the
electromagnetic force applied by the coil 40 to be substantially
proportional to the intensity sound coded in the digital input
signal.
[0251] The electromagnetic field controller 30 typically controls
an alternating current flow to the coil 40 that typically surrounds
the entire array of moving elements 10, thus creating and
controlling the magnetic field across the entire array. In certain
embodiments a power amplifier 811 may be used to boost current to
the coil 40. The electromagnetic field controller 30 typically
generates an alternating electromagnetic force whose alternation is
synchronous with the system clock 805 as described in detail below
with reference to FIG. 11A, graph I.
[0252] The latch controller 50 is operative to receive the digital
input signal 801 and to control the latching mechanism 20
accordingly. Typically, each individual moving element 10 performs
at most one transition per clock i.e. during one given clock, each
moving element may move from its bottom position to its top
position, or move from its top position to its bottom position, or
remain at one of either of those two positions. A preferred mode of
operation of the latch controller 50 is described below with
reference to FIG. 11A. According to a preferred embodiment of the
present invention, retention of moving elements 10 in their
appropriate end positions is affected by the latching controller
50.
[0253] Preferably, the latching controller 50 operates on the
moving elements in groups, termed herein "controlled groups". All
moving elements in any given group of moving elements are
selectably either latched into their top positions, or into their
bottom positions, or are unlatched. Preferably, the "controlled
groups" form a sequence G1, G2, . . . and the number of speaker
elements in each controlled group Gk is an integer, such as 2, to
the power of (k-1), thereby allowing any desired number of speaker
elements to be operated upon (latched upward, downward or not at
all) since any given number can be expressed as a sum of powers of,
for example, two or ten or another suitable integer. If the total
number of speaker elements is selected to be one less than an
integral power (N) of 2 such as 2047, it is possible to partition
the total population of speaker elements into an integral number of
controlled groups namely N. For example, if there are 2047 speaker
elements, the number of controlled groups in the sequence G1, G2, .
. . is 11.
[0254] In this embodiment, since any individual value of the
re-scaled PCM signal can be represented as a sum of integral powers
of 2, a suitable number of speaker elements can always be placed in
the selected end-position by collectively bringing all members of
suitable controlled groups into that end-position. For example, if
at time t the value of the re-scaled PCM signal is 100, then since
100=64+32+4, groups G3, G6 and G7 together include exactly 100
speaker elements and therefore, at the time t, all members of these
three groups are collectively brought to the selected end position
such as the "up" or "top" position and, at the same time, all
members of all groups other than these three groups are
collectively brought to the un-selected end position such as the
"down" or "bottom" position. It is appreciated that each moving
element has bottom and top latches, each typically generated by
selectively applying suitable local electrostatic forces,
associated therewith to latch it into its "down" and "up" positions
respectively. The set of bottom and top latches of the speaker
elements in group Gk are termed Bk and Tk latches respectively.
[0255] FIG. 8D is a simplified flowchart illustration of a
preferred method for initializing the apparatus of FIGS. 1A-8C.
According to the method of FIG. 8D, the array of moving elements 10
is put into initial motion including bringing each moving element
10 in the array of moving elements into at least one latching
position. As described herein, both top and bottom latching
positions are typically provided for each moving element 10 in
which case the step of bringing each moving element in the array
into at least one latching position typically comprises bringing a
first subset of the moving elements in the array into their top
latching positions and a second subset, comprising all remaining
elements in the array, into their bottom latching positions. The
first and second subsets are preferably selected such that when the
moving elements in the first and second subsets are in their top
and bottom latching positions respectively, the total pressure
produced by fluid such as air displaced by the moving elements 10
in the first subset is equal in magnitude and opposite in direction
to the total pressure produced by fluid such as air displaced by
the moving elements in the second subset.
[0256] The moving elements 10 typically bear a charge having a
predetermined polarity and each of the moving elements defines an
individual natural resonance frequency which tends to differ
slightly from that of other moving elements due to production
tolerances, thereby to define a natural resonance frequency range,
such as 42-46 KHz, for the array of moving elements. As described
herein, typically, first and second electrostatic latching elements
are provided which are operative to latch the moving elements 10
into the top and bottom latching positions respectively and the
step of putting the array of moving elements into motion
comprises:
[0257] Step 850: Charge the first (top or bottom) electrostatic
latch of each moving element included in the first subset with a
polarity opposite to the pole, on the moving element, facing that
latch. The first and second subsets may each comprise 50% of the
total number of moving elements.
[0258] Step 855: Charge the second (bottom or top) electrostatic
latch of each moving element included in the second subset with a
polarity opposite to the pole, on the moving element, facing that
latch.
[0259] Step 860: As described above, the moving elements are
designed to have a certain natural resonance frequency, f.sub.r.
Design tools may include computer aided modeling tools such as
finite elements analysis (FEA) software. In step 860, f.sub.CLK,
the frequency of the system clock, which determines the timing of
the alternation of the electromagnetic field in which the moving
elements are disposed, is set to the natural resonance frequency of
the moving element in the array which has the lowest natural
resonance frequency, referred to as f.sub.min and typically
determined experimentally or by computer-aided modeling.
[0260] Steps 865-870: The system clock frequency may then be
monotonically increased, from an initial value of f.sub.min to
subsequent frequency values separated by .DELTA.f until the system
clock frequency has reached the natural resonance frequency of the
moving element in the array which has the highest natural resonance
frequency, referred to as f.sub.max and typically determined
experimentally or by computer-aided modeling. It is appreciated
however that alternatively the system clock frequency might be
monotonically decreased, from f.sub.max to f.sub.min, or might be
varied non-monotonically.
[0261] It is appreciated that when a moving element 10 is excited
at its natural resonance frequency, f.sub.r, the moving element
increases its amplitude with every cycle, until reaching a certain
maximal amplitude termed hereinafter A.sub.max. Typically, the
duration .DELTA.t required for the moving element to reach
A.sub.max is recorded during set-up and the magnetic force applied
during the initialization sequence is selected to be such that
A.sub.max is twice as large as the gap the moving element needs to
travel from its idle state to either the top or bottom latch.
[0262] The Q factor or quality factor is a known factor which
compares the time constant for decay of an oscillating physical
system's amplitude to its oscillation period. Equivalently, it
compares the frequency at which a system oscillates to the rate at
which it dissipates its energy. A higher Q indicates a lower rate
of energy dissipation relative to the oscillation frequency.
Preferably, the Q factor of the moving elements is determined
either computationally or experimentally. The Q factor as
determined describes how far removed the frequency f.sub.CLK needs
to be from f.sub.r (two possible values, one below f.sub.r and one
above f.sub.r) before the amplitude drops to 50% of A.sub.max. The
difference between the two possible values is .DELTA.f.
[0263] As a result of the above steps, a sequence of
electromagnetic forces of alternating polarities is now applied to
the array of moving elements. The time interval between consecutive
applications of force of the same polarity varies over time due to
changes induced in the system clock, thereby to define a changing
frequency level for the sequence. This results in an increase, at
any time t, of the amplitude of oscillation of all moving elements
whose individual natural resonance frequency is sufficiently
similar to the frequency level at time t. The frequency level
varies sufficiently slowly (i.e. only after a suitable interval
.DELTA.t, which may or may not be equal in all iterations) to
enable the set S, of all moving elements whose natural resonance
frequency is similar to the current frequency level, to be latched
before the electromagnetic field alternation frequency level
becomes so dissimilar to their natural resonance frequency as to
cease increasing the amplitude of oscillation of the set S of
moving elements. The extent of variation of the frequency level
corresponds to the natural resonance frequency range. Typically, at
the end of the initiation sequence (step 872), the system clock
f.sub.CLK is set to the predefined system frequency, typically
being the average or median natural resonance frequency of the
moving elements in the array, i.e. 44 KHz.
[0264] One method for determining the range of the natural
resonance frequencies of the moving elements is to examine the
array of moving elements using a vibrometer and excite the array at
different frequencies.
[0265] FIG. 8E is a simplified isometric view illustration of an
assembled speaker system constructed and operative in accordance
with a preferred embodiment of the present invention. Mounted on a
PCB 2100 is the array of actuator elements including moving
elements 10 (not shown) sandwiched between latching elements 20.
The array is surrounded by coil 40. Control lines 2110 are shown
over which the latch control signals generated by latch controller
50 (not shown) in processor 802 travel to the latch elements 20.
Amplifier 811 amplifies signals provided by the magnetic field
generation controller 30 (not shown) in processor 802 to the coil
40. A connector 2120 connects the apparatus of FIG. 8E to a digital
sound source. For simplicity, conventional components such as power
supply components are not shown.
[0266] A preferred method of operation for generating a sound using
apparatus constructed and operative in accordance with an
embodiment of the present invention is now described based on FIG.
8F. The method of FIG. 8F is preferably based on the sound's
representation in the time domain, typically a PCM (pulse-code
modulation) representation.
[0267] Resampler 814 of FIG. 8F: Unless the sampling rate of the
PCM happens to be the same as the system clock, the PCM is
resampled to bring its sampling rate up to or down to the system
clock frequency (top row in FIG. 11A) of the apparatus of FIG.
1A.
[0268] Generally, any suitable sampling rate may be employed.
Specifically, the system of the present invention generates sound
waves having at least two different frequencies, one of which is
the desired frequency as determined by the input signal and the
other of which is an artifact. The artifact frequency is the clock
frequency i.e. the sampling rate of the system. Therefore,
preferably, the system sampling rate is selected to be outside of
the human hearing range i.e. at least 20 KHz. Nyquist sampling
theory teaches that the system clock must be selected to be at
least double that of the highest frequency the speaker is designed
to produce.
[0269] Scaler 815: The PCM word length is typically 8, 16 or 24
bits. 8 bit PCM representations are unsigned, with amplitude values
varying over time from 0 to 255, and 16 and 24 bit PCM
representations are signed, with amplitude values varying over time
from -32768 to 32767 and -8388608 to 8388607 respectively. The
speaker of FIGS. 1-2C typically employs an unsigned PCM signal and
therefore, if the PCM signal is signed e.g. if the PCM word length
is 16 or 24 bits, a suitable bias is added to obtain a
corresponding unsigned signal. If the PCM word length is 16 bits, a
bias of 32768 amplitude units is added to obtain a new range of
0-65535 amplitude units. If the PCM word length is 24 bits, a bias
of 8388608 amplitude units is added to obtain a new range of
0-16777215 amplitude units.
[0270] The PCM signal is then further re-scaled as necessary such
that its range, in amplitude units, is equal to the number of
speaker elements in the apparatus of FIGS. 1-2C. For example, if
the number of speaker elements is 2047, and the PCM signal is an 8
bit signal, the signal is multiplied by a factor of 2048/256=8. Or,
if the number of speaker elements is 2047, and the PCM signal is a
16 bit signal, the signal is multiplied by a factor of
2048/65536=1/32.
[0271] Sound is then generated to represent the re-scaled PCM
signal by actuating a suitable number of speaker elements in
accordance with the current value of the re-scaled PCM signal. It
is appreciated that the speaker elements have two possible
end-states, termed herein the "down" and "up" end-states
respectively, and illustrated schematically in FIGS. 2A and 2B
respectively. An individual one of these end-states is selected and
the number of speaker elements in that end-state at any given time
matches the current value of the re-scaled PCM signal, the
remaining speaker elements at the same time being in the opposite
end-state. For example, if there are 2047 speaker elements, the
selected end-state is "up" and the value of the re-scaled PCM
signal at time t is 100, the number of speaker elements in the "up"
and "down" end states at time t are 100 and 1947 respectively.
According to certain embodiments of the invention, there is no
importance to the particular speaker elements selected to be in the
"up" state as long as their total number corresponds to the current
value of the re-scaled PCM signal.
[0272] The following loop is then performed M times each time a
sample is generated by scaler 815. M is the number of actuator
elements in the apparatus of FIG. 1A. i is the index of the current
loop. V.sub.t is used to designate the current sample value exiting
scaler 815 (for which M iterations of the loop are being
performed). Generally, the number of moving elements to be latched
into their top positions, is exactly equal to the value of V.sub.t
and all remaining moving elements are to be latched into their
bottom positions. Therefore, while i is still smaller than V.sub.t,
the i'th moving element or pixel, termed in FIG. 8F "Pi" is latched
to its top position. This is done by checking (FIG. 8F, step 840)
whether, when moving element i was processed in the previous loop
(t-1), it was in its top latching position or in its bottom
latching position. If the former was the case, nothing needs to be
done and the method jumps to incrementation step 842. If the latter
was the case, element i is marked as an element which needs to be
latched into its top position (step 839). To latch all remaining
moving elements into their bottom positions, do the following for
all moving elements whose index exceeds V.sub.t: check (step 838)
which are already in their bottom positions; these moving elements
need no further treatment. All others are marked (step 841) as
elements which need to be latched into their bottom positions. Once
all M elements have been marked or not marked as above, perform the
following:
[0273] Verify that the magnetic field points upward, or wait for
this (step 843), and, for the V.sub.t or less pixels which are to
be raised, discharge the bottom latches and charge the top latches
(step 844). Next, wait for the magnetic field to point downward
(step 845), and, for the (M-V.sub.t) or less pixels which are to be
lowered, discharge the top latches and charge the bottom latches
(step 846). At this point, the flow waits for the next sample to be
produced by scaler 815 and then begins the M iterations of the loop
just described for that sample.
[0274] It is appreciated that steps preceding step 843 are
preferably executed during the half clock cycle in which the
magnetic field polarity is downwards. Step 844 is preferably
executed at the moment the magnetic field changes its polarity from
downwards to upwards. Similarly, step 846 is preferably executed at
the moment the magnetic field changes polarity again from upwards
to downwards. It is also appreciated that in order for the device
to remain synchronized with the digitized input signal, steps
814-846 are all preferably executed in less than one clock
cycle.
[0275] FIG. 9A is a graph summarizing the various forces brought to
bear on moving elements 10 in accordance with a preferred
embodiment of the present invention.
[0276] FIG. 9B is a simplified pictorial illustration of a magnetic
field gradient inducing layer constructed and operative in
accordance with a preferred embodiment of the present invention and
comprising at least one winding conductive element 2600 embedded in
a dielectric substrate 2605 and typically configured to wind
between an array of channels 2610. Typically, there are no channels
2610 along the perimeter of the conductive layer of FIG. 9B so that
the gradient induced within channels adjacent the perimeter is
substantially the same as the gradient induced in channels adjacent
the center of the conductive layer.
[0277] If the layer of FIG. 9B is separate from the spacer layers
described above, then the channels in the layer of FIG. 9B are
disposed opposite and as a continuation of the channels in the
spacer layers described in detail above. The cross-sectional
dimensions, e.g. diameters, of channels 2610 may be different than
the diameters of the channels in the spacer layer. Alternatively,
the layer of FIG. 9B may serve both as a spacer layer and as a
magnetic field inducing layer in which case the channels 2610 of
FIG. 9B are exactly the spacer layer channels described
hereinabove. It is appreciated that, for simplicity, the electrodes
forming part of the spacer layer are not shown in FIG. 9B.
[0278] FIGS. 9C and 9D illustrate the magnetic field gradient
induction function of the conductive layer of FIG. 9B. In FIG. 9C,
the current flowing through the winding element 2600 is indicated
by arrows 2620. The direction of the resulting magnetic field is
indicated by X's 2630 and encircled dots 2640 in FIG. 9C,
indicating locations at which the resulting magnetic field points
into and out of the page, respectively.
[0279] FIG. 10A is a simplified top cross-sectional illustration of
a latching layer included in latch 20 of FIG. 1A in accordance with
a preferred embodiment of the present invention. The latching layer
of FIG. 10A is suitable for latching moving elements partitioned
into several groups G1, G2, . . . whose latches are electrically
interconnected as shown so as to allow collective actuation of the
latches. This embodiment is typically characterized in that any
number of moving elements may be actuated by collectively charging
the latches of selected groups from among the partitioned groups,
each latch in the latching layer typically being associated with a
permanent magnet, wherein the poles of all of the permanent magnets
in the latching layer are all identically disposed. Each group Gk
may comprise 2 to the power of (k-1) moving elements. The groups of
moving elements may spiral out from the center of the array of
moving elements, smallest groups being closest to the center as
shown.
[0280] FIG. 10B is a simplified electronic diagram of an
alternative embodiment of the latching layer of FIG. 10A in which
each latch is individually rather than collectively controlled
(i.e. charged) by the latching controller 50 of FIG. 1A. It is
appreciated that the latches are shown to be annular, however
alternatively they may have any other suitable configuration e.g.
as described herein. The layer of FIG. 10B comprises a grid of
vertical and horizontal wires defining junctions. A gate such as a
bi-polar field-effect transistor is typically provided at each
junction. To open an individual gate thereby to charge the
corresponding latch, suitable voltages are provided along the
corresponding vertical and horizontal wires.
[0281] FIG. 11A is a timing diagram showing a preferred charging
control scheme which may be used by the latch controller 50 in FIG.
1A in uni-directional speaker applications wherein an input signal
representing a desired sound is received, and moving elements 10
constructed and operative in accordance with a preferred embodiment
of the present invention are controlled responsively, by
appropriate charging of their respective latches, so as to obtain a
sound pattern in which the volume in front of the speaker is
greater than in other areas, each latch in the latching layer being
associated with a permanent magnet, and the poles of all of the
permanent magnets in the latching layer all being identically
disposed. FIG. 11B is a schematic illustration of an example array
of moving elements 10 to which the timing diagram of FIG. 11A
pertains.
[0282] A preferred mode of operation of the latch controller 50 is
now described with reference to FIGS. 11A-B. For clarity, the
preferred mode of operation is described merely by way of example
with reference to a speaker comprising 7 pixels numbered P1, P2, .
. . P7 as shown in FIG. 11B. Further according to the example used
to explain the preferred mode of operation of latch controller 50,
the 7 pixels are actuated in three groups comprising 1, 2 and 4
pixels respectively. Generally, the latch controller 50 uses
various decision parameters, as described in detail herein, to
determine how to control each individual moving element in each
time interval. Speakers constructed and operative in accordance
with a preferred embodiment of the present invention are typically
operative to reproduce a sound which is represented by the analog
signal of Graph II and is then digitized and supplied to a speaker
of the present invention. The values of the digital signal are
shown in FIG. 11A, graph III.
[0283] Graph IV shows the alternation of the electromagnetic force
applied to the moving elements 10 by the coil or other magnetic
field generator 40. Graph V is the signal provided by latching
controller 50 to the top latch of an individual moving element, P1
seen in FIG. 11B, forming, on its own, a first group G1 of moving
elements consisting only of P1. Graph VI is the signal provided by
latching controller 50 to the bottom latch of P1. The states of P1,
due to the operation of the latches associated therewith, are shown
in Graph VII, in which black indicates the top extreme position in
which the top latch engages P1, white indicates the bottom extreme
position in which the bottom latch engages P1, and hatching
indicates intermediate positions.
[0284] Graph VIII is the signal provided by latching controller 50
to the top latch/es of each of, or both of, moving elements P2 and
P3 seen in FIG. 11B, which together form a second group GII of
moving elements. Graph IX is the signal provided by latching
controller 50 to the bottom latch/es of GII. The states of P2 and
P3, due to the operation of the latches associated therewith, are
shown in Graphs X and XI respectively, in which black indicates the
top extreme position in which the top latch engages the relevant
moving element, white indicates the bottom extreme position in
which the bottom latch engages the relevant moving element, and
hatching indicates intermediate positions of the relevant moving
element.
[0285] Graph XII is the signal provided by latching controller 50
to the top latch/es of each of, or all of, moving elements P4-P7
seen in FIG. 11B, which together form a third group GIII of moving
elements. Graph XIII is the signal provided by latching controller
50 to the bottom latch/es of G111. The states of P4-P7, due to the
operation of the latches associated therewith, are shown in Graphs
XIV-XVII respectively, in which black indicates the top extreme
position in which the top latch engages the relevant moving
element, white indicates the bottom extreme position in which the
bottom latch engages the relevant moving element, and hatching
indicates intermediate positions of the relevant moving
element.
[0286] Graph XVIII schematically illustrates the moving elements
P1-P7 of FIG. 11B in their various positions, as a function of
time.
[0287] For example, in interval I5, the clock is high (graph I),
the digitized sample value is 2 (graph III), which indicates that 5
elements need to be in their top positions and 2 elements in their
bottom positions as shown in interval I5 of Graph XVIII. Since
latch actuation in this embodiment is collective, this is achieved
by selecting groups G1 and G3 which together have 5 elements (1+4)
to be in their top positions whereas the two moving elements in G2
will be in their bottom positions. The magnetic field points upward
in interval I5 as shown in Graph IV. In interval I4, the moving
element in G1 was in its bottom position as shown in Graph XVIII
and therefore needs to be raised. To do so, control signal B1 is
lowered (graph VI) and control signal T1 is raised (graph V). As a
result, the moving element of G1 assumes its top position as shown
in graph VII. In interval I4, the moving elements in G2 are already
in their bottom positions as shown in Graph XVIII and therefore the
top control signal T2 remains low as seen in graph VIII, the bottom
control signal B2 remains high as seen in graph IX and
consequently, as shown in Graphs X and XI respectively, the two
moving elements (P2 and P3) in G2, remain in their bottom extreme
positions. As for group G3, in interval I4, the moving elements in
G3 are already in their top positions as shown in Graph XVIII and
therefore the top control signal T3 remains high as seen in graph
XII, the bottom control signal B3 remains low as seen in graph XIII
and consequently, as shown in Graphs XIV-XVII respectively, the
four moving elements (P4-P7) in G3, remain in their top extreme
positions.
[0288] Preferably, when the input signal in graph II is at a
positive local maximum, all moving elements are in their top
position. When the input signal is at a negative local maximum, all
moving elements are in their bottom position.
[0289] FIG. 11C is a timing diagram showing a preferred control
scheme used by the latch controller 50 in omni-directional speaker
applications wherein an input signal representing a desired sound
is received, and moving elements constructed and operative in
accordance with a preferred embodiment of the present invention are
controlled responsively, so as to obtain a sound pattern in which
the loudness of the sound in an area located at a certain distance
in front of the speaker is similar to the loudness in all other
areas surrounding the speaker at the same distance from the
speaker.
[0290] As shown, the step of selectively latching comprises
latching specific moving elements at a time determined by the
distance of the specific moving elements from the center of the
array (e.g. as indicated by r in the circular array of FIG. 11B).
Typically, when it is desired to latch a particular subset of
moving elements, typically corresponding in number to the intensity
of a desired sound, the moving elements are latched not
simultaneously but rather sequentially, wherein moving elements
closest to the center are latched first, followed by those moving
elements disposed, typically in layers, concentrically outward from
the center. Typically, the moving elements in each layer are
actuated simultaneously. Typically, the temporal distance .DELTA.t
between the moment at which a particular moving element is latched
and between the moment at which the first, central, moving element
or elements was or were latched is r/c where c is the speed of
sound.
[0291] It is appreciated that the moving elements in graph X of
FIG. 11C are shown to comprise flexible peripheral portions,
however this is merely by way of example and is not intended to be
limiting.
[0292] FIGS. 12A and 12B are respectively simplified top view and
cross-sectional view illustrations of the moving element layer in
accordance with a preferred embodiment of the present invention in
which half of the permanent magnets are placed north pole upward
and half north pole downward. A particular advantage of this
embodiment is that moving elements can be raised both when the
electromagnetic field points upward and when it points downward
rather than waiting for the field to point upward before lifting a
moving element and waiting for the field to point downward before
lowering a moving element. Although the illustrated embodiment
shows the two subsets separated from one another, this not need be
the case. The two subsets may be interleaved with one another.
[0293] FIG. 13 is a simplified top view illustration similar to
FIG. 10A except that half of the permanent magnets in the latching
layer are disposed north pole upward and the remaining half of the
permanent magnets in the latching layer are disposed north pole
downward. Whereas in the embodiment of FIG. 10A, there was one
group each of size 1, to 2, 4, . . . (which may be arranged
sequentially around the center as shown in FIG. 10A although this
need not be the case) in the embodiment of FIG. 13, there are two
groups of each size, thereby generating two sequences of groups of
size 1, 2, 4, . . . . In the illustrated embodiment the groups in
the first sequence are termed G1L, G2L, G3L, and the groups in the
first sequence are termed G1R, G2R, G3R, . . . . Each of these
sequences is arranged within one semicircle, such as the left and
right semicircles as shown. The arrangement of the groups within
its semicircle need not be in order of size of the group extending
concentrically outward as shown and can be any desired arrangement,
however, preferably, both groups are arranged mutually
symmetrically within their individual semicircle. It is appreciated
that by using suitable coil designs, the same effect can be
achieved using permanent magnets that are all polarized in the same
direction while the coil generates magnetic fields having a certain
polarization across half of the moving elements and having an
opposite polarization across the other half.
[0294] A particular feature of the embodiments of FIGS. 10A and 13
is that latch elements corresponding to certain moving elements are
electrically interconnected thereby to form groups of moving
elements which can be collectively latched or released by
collectively charging or discharging, respectively, their
electrically interconnected latches.
[0295] FIG. 14 is a control diagram illustrating control of the
latches and of the coil-induced electromagnetic force for a
particular example in which the moving elements are arranged in
groups that can each, selectively, be actuated collectively,
similar to FIG. 8A except that half of the permanent magnets in the
latching layer are disposed north pole upward and the remaining
half of the permanent magnets in the latching layer are disposed
north pole downward as shown in FIG. 13, whereas in FIG. 8A, the
poles of all of the permanent magnets in the latching layer are all
identically disposed. As shown in FIG. 14, latching signals are
provided to all of groups G1L, G2L, G3L, . . . and G1R, G2R, G3R.
The top latching signals for these groups are indicated as LT1,
LT2, LT3, . . . and RT1, RT2, RT3 respectively. The bottom latching
signals for these groups are indicated as LB1, LB2, LB3, and RB1,
RB2, RB3.
[0296] FIG. 15A is a timing diagram showing a preferred control
scheme used by the latch controller 50 in uni-directional speaker
applications, which is similar to the timing diagram of FIG. 11A
except that half of the permanent magnets in the latching layer are
disposed north pole upward and the remaining half of the permanent
magnets in the latching layer are disposed north pole downward as
shown in FIG. 13 whereas in FIG. 11A the poles of all of the
permanent magnets in the latching layer are all identically
disposed. FIG. 15B is a schematic illustration of an example array
of moving elements to which the timing diagram of FIG. 15A
pertains.
[0297] As described above, a particular advantage of the embodiment
of FIGS. 13-15A as opposed to the embodiment of FIGS. 8A, 10A and
11A is that moving elements can be raised both when the
electromagnetic field points upward and when it points downward
rather than waiting for the field to point upward before lifting a
moving element and waiting for the field to point downward before
lowering a moving element. It is appreciated that no elements move
in 50% of the time slots in FIG. 11A which may introduce distortion
of sound and is relatively inefficient. In contrast, elements move
in 100% of the time slots in FIG. 15A (other than slots in which no
motion is required since the digital signal value is unchanged)
thereby preventing distortion and enhancing efficiency.
[0298] For example, in interval I5, the digitized signal value
changes from 1 to 2 as shown in graph II of FIGS. 11A and 15A.
Consequently, moving element P1 in FIG. 11A needs to be raised i.e.
released from its current, bottom extreme position and latched into
its top extreme position, however whereas in I5, control signal B1
is lowered and control signal T1 is raised, in interval I6 nothing
happens. In FIG. 15A, in contrast, where moving elements LP1 (and
RP1) need to be raised, control signal LB1 is lowered and control
signal LT1 is raised in interval I5, and immediately afterward, in
interval I6, the RB1 control signal is lowered and the RT1 signal
is raised, resulting in upward motion of RP1 without the delay
incurred in FIG. 11A.
[0299] Generally in the embodiment of FIGS. 13-15A, since half of
the magnets (say, the left half) point north up and the remaining
(right) half point north down, when it is desired to move elements
10 upward, this can always be done without delay. If the magnetic
field points up, the moving elements in the left half of the array
can be moved upward before those in the right half, whereas if by
chance the magnetic field is found to be pointing down, the moving
elements in the right half of the array can be moved upward before
those in the left half.
[0300] FIG. 15C is a graph showing changes in the number of moving
elements disposed in top and bottom extreme positions at different
times and as a function of the frequency of the input signal
received by the latching controller 50 of FIG. 1A.
[0301] FIG. 16A is an isometric view illustration of a moving
element layer which is an alternative to the moving element layer
shown in FIGS. 1A and 2A-2C in which the layer is formed from a
thin foil such that each moving element comprises a central portion
and surrounding portions.
[0302] FIG. 16B is an isometric view illustration of still another
alternative to the moving element layer shown in FIGS. 1A and 2A-2C
in which the flexure structure at the periphery of each moving
element comprises a sheet of flexible material e.g. rubber. The
central area of each moving element comprises a magnet which may or
may not be mounted on a rigid disc.
[0303] FIG. 16C is an isometric view of a preferred embodiment of
the moving elements and surrounding flexures depicted in FIG. 7A-7E
or 16A in which flexures vary in thickness. In FIG. 16C, for
simplicity, the component which causes the moving element 1620 to
be affected by the magnetic field, which component may preferably
comprise a magnet or alternatively, a ferro-magnet, conductive
material or coil, is not shown. As shown, the moving element 1620
comprises serpentine peripheral flexures 1630 having portions of
varying thicknesses connecting a central portion 1640 of the moving
element to a sheet 1650 interconnecting all or many moving
elements. For example, the portions of varying thicknesses may
include thicker portions 1660 and thinner portions 1670
respectively as shown. For example, if the diameter of the central
portion 1640 of each moving element is 300 microns and the sheet is
silicon, then under certain conditions, portions 1670 may be 50
microns thick whereas portions 1660 may be 100 microns thick. More
generally, thicknesses are computed as a function of materials to
provide application-specific flexibility and strength levels, e.g.
using FEA (finite element analysis) tools.
[0304] FIG. 16D is an isometric illustration of a cost effective
alternative to the apparatus of FIG. 16C in which flexures vary in
width. As in FIG. 16C, for simplicity, the component which causes
the moving element 1720 to be affected by the magnetic field, which
component may preferably comprise a magnet or alternatively, a
ferro-magnet, conductive material or coil, is not shown. As shown,
the moving element 1720 comprises serpentine peripheral flexures
1730 having portions of varying widths connecting a central portion
1740 of the moving element to a sheet 1750 interconnecting all or
many moving elements. For example, the portions of varying widths
may include wider portions 1760 and narrower portions 1770
respectively as shown. For example, if the diameter of the central
portion 1740 of each moving element is 300 microns and the sheet is
silicon, then under certain conditions, portions 1770 may be 20
microns wide whereas portions 1760 may be 60 microns wide. More
generally, widths are computed as a function of materials to
provide application-specific flexibility and strength levels, e.g.
using FEA (finite element analysis) tools.
[0305] It is appreciated that the embodiments of FIGS. 16C and 16D
may be suitably combined, e.g. to provide flexures with varying
thicknesses and varying widths, and/or varied, e.g. to provide
flexures whose widths and/or thicknesses vary either continuously
or discontinuously as shown, and either regularly as shown or
irregularly.
[0306] In the above description, "thickness" is the dimension of
the flexure in the direction of motion of the moving element
whereas "width" is the dimension of the flexure in the direction
perpendicular to the direction of motion of the moving element.
[0307] A particular advantage of the embodiments of FIGS. 16C and
16D is that in flexures of varying cross-sections, e.g. varying
thicknesses or widths, the stress is not concentrated at the roots
1680 or 1780 of the flexures and is instead distributed over all
the thin and/or narrow portions of the flexures. Also, generally,
the stress on the flexures as a result of bending thereof is a
steep function of the thickness, typically a cubic function
thereof, and is also a function of the width, typically a linear
function thereof. It is believed to be impractical, at least for
certain materials such as silicon and at least for certain
applications employing large displacement of the moving elements,
e.g. public address speakers, to select flexure dimensions which
are uniformly thin enough or narrow enough to provide sufficiently
low stress so as to prevent breaking, and simultaneously stiff
enough to allow natural resonance frequency at a desirable range
e.g. 44 KHz. For this reason as well, it is believed to be
advantageous to use flexures of varying thicknesses and/or widths
e.g. as illustrated in FIGS. 16C-16D.
[0308] FIG. 17 is a top cross-sectional view illustration of an
array of actuator elements similar to the array of FIG. 3A except
that whereas in FIG. 3A, consecutive rows of individual moving
elements or latches are respectively skewed so as to increase the
number of actuator elements that can be packed into a given area,
the rows in FIG. 17 are unskewed and typically comprise a
rectangular array in which rows are mutually aligned.
[0309] FIG. 18 is an exploded view of an alternative embodiment of
an array of actuator elements, including a layer 1810 of moving
elements sandwiched between a top latching layer 1820 and a bottom
latching layer 1830. The apparatus of FIG. 18 is characterized in
that the cross-section of each actuator element is square rather
than round. Each actuator element could also have any other
cross-sectional shape such as a hexagon or triangle.
[0310] FIG. 19 is an isometric array of actuators supported within
a support frame providing an active area which is the sum of the
active areas of the individual actuator arrays. In other words, in
FIG. 19, instead of a single one actuating device, a plurality of
actuating devices is provided. The devices need not be identical
and can each have different characteristics such as but not limited
to different clock frequencies, different actuator element sizes
and different displacements. The devices may or may not share
components such as but not limited to coils 40 and/or magnetic
field controllers 30 and/or latch controller 50.
[0311] The term "active area" refers to the sum of cross-sectional
areas of all actuator elements in each array. It is appreciated
that generally, the range of sound volume (or, for a general
actuator other than a speaker, the gain) which can be produced by a
speaker constructed and operative in accordance with a preferred
embodiment of the present invention is often limited by the active
area. Furthermore, the resolution of sound volume which can be
produced is proportional to the number of actuator elements
provided, which again is often limited by the active area.
Typically, there is a practical limit to the size of each actuator
array e.g. if each actuator array resides on a wafer.
[0312] If the speaker is to serve as a headphone, only a relatively
small range of sound volume need be provided. Home speakers
typically require an intermediate sound volume range whereas public
address speakers typically have a large sound volume range, e.g.
their maximal volume may be 120 dB. Speaker applications also
differ in the amount of physical space available for the speaker.
Finally, the resolution of sound volume for a particular
application is determined by the desired sound quality. e.g. cell
phones typically do not require high sound quality, however space
is limited.
[0313] According to certain embodiments of the present invention,
layers of magnets on the moving elements may be magnetized so as to
be polarized in directions other than the direction of movement of
the element to achieve a maximum force along the electromagnetic
field gradient aligned with the desired element moving
direction.
[0314] Referring again to FIGS. 12A-15B inter alia, it is
appreciated that if the coil used is of a design that utilizes
conductors carrying current on both sides of the elements, and the
magnets are all polarized in the same direction, then the elements
on one side of each conductor would move in opposite directions
when current flows in the coil.
[0315] A particular feature of a preferred embodiment of the
present invention is that the stroke of motion performed by the
moving elements is relatively long because the field applied
thereto is magnetic hence decays at a rate which is inversely
proportional to the distance between the moving elements and the
current producing the magnetic field. In contrast, an electrostatic
field decays at a rate which is inversely proportional to the
square of the distance between the moving elements and the electric
charge producing the electrostatic field. As a result of the long
stroke achieved by the moving elements, the velocity achieved
thereby is increased hence the loudness that can be achieved
increases because the air pressure generated by the high velocity
motion of the moving elements is increased.
[0316] It is appreciated that the embodiments specifically
illustrated herein are not intended to be limiting e.g. in the
sense that the moving elements need not all be the same size, the
groups of moving elements, or individual moving elements if
actuated individually, need not operate at the same resonance nor
with the same clock, and the moving elements need not have the same
amplitude of displacement.
[0317] The speaker devices shown and described herein are typically
operative to generate a sound whose intensity corresponds to
intensity values coded into an input digital signal. Any suitable
protocol may be employed to generate the input digital signal such
as but not limited to PCM or PWM (SACD) protocols. Alternatively or
in addition the device may support compressed digital protocols
such as ADPCM, MP3, AAC, or AC3 in which case a decoder typically
coverts the compressed signal into an uncompressed form such as
PCM.
[0318] Design of digital loudspeakers in accordance with any of the
embodiments shown and described herein may be facilitated by
application-specific computer modeling and simulations. Loudness
computations may be performed conventionally, e.g. using fluid
dynamic finite-element computer modeling and empiric
experimentation.
[0319] Generally, as more speaker elements (moving elements) are
provided, the dynamic range (difference between the loudest and
softest volumes that can be produced) becomes wider, the distortion
(the less the sound resembles the input signal) becomes smaller and
the frequency range becomes wider. On the other hand, if less
speaker elements are provided, the apparatus is smaller and less
costly.
[0320] Generally, if the moving elements have large diameters, the
ratio between active and inactive areas (the fill factor) improves,
and there is less stress on the flexures if any, assuming that the
vibration displacement remains the same, which translates into
longer life expectancy for the equipment. On the other hand, if the
moving elements have small diameters, more elements are provided
per unit area, and due to the lesser mass, less current is required
in the coil or other electromagnetic force generator, translating
into lower power requirements.
[0321] Generally, if the vibration displacement of the moving
elements is large, more volume is produced by an array of a given
size, whereas if the same quantity is small, there is less stress
on the flexures, if any, and the power requirements are lower.
[0322] Generally, if the sample rate is high, the highest
producible frequency is high and the audible noise is reduced. On
the other hand, if the sample rate is low, accelerations, forces,
stress on flexures if any and power requirements are lower.
[0323] Three examples of application-specific speakers are now
described.
Example 1
[0324] It may be desired to manufacture a mobile phone speaker
which is very small, is low cost, is loud enough to be heard
ringing in the next room, but has only modest sound quality. The
desired small size and cost suggest a speaker with relatively small
area, such as up to 300 mm.sup.2. If a relatively high target
maximal loudness such as 90 dB SPL is desired, this suggests large
displacement. Acceptable distortion levels (10%) and dynamic range
(60 dB) in mobile phone speakers dictate a minimal array size of
1000 elements (computed using: M=10.sup.(60/20). Therefore, a
suitable speaker may comprise 1023 moving elements partitioned into
10 binary groups, each occupying an area of about 0.3 mm.sup.2. The
cell size would therefore be about 550 .mu.m.times.550 .mu.m.
[0325] For practical reasons, the largest moving element that fits
this space may have a diameter of 450 .mu.m. Reasonable
displacement for such a moving element may be about 100 .mu.m PTP
(peak to peak) which enables the target loudness to be achieved.
The sample rate may be low, e.g. 32 KHz, since mobile phones sound
is limited by the cellular channel to 4 KHz.
Example 2
[0326] It may be desired to manufacture high fidelity headphones
having very high sound quality (highest possible) and very low
noise, and which are additionally small enough to be worn
comfortably, and finally, cost-effective to the extent
possible.
[0327] To achieve high sound quality, wide dynamic range (at least
96 dB), wide frequency range (20 Hz-20 KHz) and very low distortion
(<0.1%) may be used. The minimal number of elements may be,
given these assumptions, 63000. So, for example, the speaker may
have 65535 elements divided into 16 binary groups. Maximal loudness
can be kept low (800) so as to allow displacements of about 30
.mu.m PTP. The smallest moving element capable of such
displacements is about 150 .mu.m in diameter. Such an element may
occupy a cell of 200 .mu.m.times.200 .mu.m or 0.04 mm.sup.2 such
that 65535 elements fit into an area of 2621 mm.sup.2 e.g. 52
mm.times.52 mm. The sample rate is typically at least twice the
highest frequency the speaker is meant to produce, or 40 KHz. The
closest standard sample rate is 44.1 KHz.
Example 3
[0328] It may be desired to manufacture a public address speaker,
e.g. for a dance club, which is very loud, has a wide frequency
range, extends to very low frequencies, and has low distortion.
Therefore, PA speakers typically have many large moving elements.
600 .mu.m moving elements may be used, which are capable of
displacements of 150 .mu.m PTP. Such elements occupy cells of 750
.mu.m.times.750 .mu.m or 0.5625 mm.sup.2. Due to the low frequency
requirement, a minimum of 262143 moving elements, partitioned into
18 binary groups, may be used. The size of the speaker may be about
40 cm.times.40 cm. This speaker typically reaches maximal loudness
levels of 120 dB SPL and extends down to 15 Hz.
[0329] Reference is now made to FIGS. 20A-20B which is are
simplified generally self-explanatory functional block diagram
illustration of preferred systems for achieving a desired
directivity pattern for a desired sound stream using a direct
digital speaker such as any of those shown herein in FIGS. 1A-19 or
such as a conventional direct digital speaker which may, for
example comprise that shown and described in U.S. Pat. No.
6,403,995 to David Thomas, assigned to Texas Instruments and issued
11 Jun. 2002, or in Diamond Brett M., et al, "Digital sound
reconstruction using array of CMOS-MEMS micro-speakers",
Transducers '03, The 12.sup.th International Conference on Solid
State Sensors, Actuators and Microsystems, Boston, Jun. 8-12,
2003.
[0330] If the direct digital speaker of FIG. 1A is used to achieve
a desired directivity pattern for a desired sound stream, then
typically, blocks 3020, 3030 and 3040 in FIG. 20A comprise blocks
20, 30 and 40 of FIG. 1A respectively and block 3050 comprises
latch controller 50 of FIG. 1A, programmed to implement the
per-clock operation of block 3050 e.g. as shown and described
herein with reference to FIG. 21.
[0331] FIG. 21 is a simplified flowchart illustration of per-clock
operation of the moving element constraint controller 3050 of FIGS.
20A-20B, in accordance with certain embodiments of the present
invention.
[0332] Step 3100 determines how many moving elements should move
during the current clock. Typically, and as described in detail
above with reference to FIGS. 1-19, the number of moving elements
which are to move during a given clock is generally proportional to
the intensity of the input signal during that clock, suitably
normalized e.g. as described above with reference to resampler 814
and scaler 815 of FIG. 8B.
[0333] Step 3200 determines which moving elements should move
during the current clock, using, in some embodiments, a suitable
moving element selection LUT which is typically loaded into the
memory of the constraint controller 3050 of FIGS. 20A-20B during
factory set-up. Each such LUT is typically built for a specific
moving element array taking into account, inter alia, the array
size and whether or not the array is skewed. Each directivity
pattern which it is desired to achieve typically requires its own
LUT.
[0334] Step 3300 determines the amount of delay with which to
operate each of the moving elements of moving element array 3010 or
3012 of FIGS. 20A-20B.
[0335] Step 3200 is now described in detail. A preferred method for
performing step 3200 is now described. Step 3200 typically employs
a LUT (look up table) which has cells which correspond one-to-one
to the pressure producing elements in the array. For example, if
the array comprises a rectangle of 100.times.200 pressure producing
elements then the LUT may have 100.times.200 cells. Each cell holds
a uniquely appearing integer between 1 and the total number of
pressure producing elements such as 20000 in the illustrated
example. Therefore, the LUT assigns an ordinal number to each
pressure producing element in the array. Associated in memory with
the LUT is a integer parameter P which stores an indication of the
number of pressure producing elements currently in a first
operative configuration from among two operative configurations,
characterized in that transition of the pressure producing elements
therebetween produces pressure in the medium, such as air, in which
the apparatus of the invention is disposed. In some embodiments,
pressure in opposite directions is obtained when the elements move
from the first configuration to the second, as opposed to when the
elements move from the second configuration to the first. In other
embodiments, pressure is obtained as long as the elements are in
the first configuration, and no pressure is obtained when the
elements are in the second configuration.
[0336] Typically, P is initialized during set-up as described
below, and is then assigned a current value in each clock by step
3100. In the immediately following step 3200 in the same clock, P
pressure producing elements are brought to their first operative
configuration and N-P pressure producing elements are brought to
their second operative configuration where N is the number of
pressure producing elements in the array. The P elements selected
to be in their first operative configuration are those whose
ordinal number as determined by the LUT is smaller than P. The N-P
elements selected to be in their second operative configuration are
those whose ordinal number as determined by the LUT is greater than
or equal to P.
[0337] One of these configurations, say the first, is typically
arbitrarily considered the "positive" configuration whereas the
other configuration, say the second, is then considered the
"negative" configuration. Alternatively, in some applications there
may be a physical reason to select a specific one of the
configurations to be the positive configuration. The pressure
generated when a pressure producing element moves from the second
configuration to this first configuration is termed "positive
pressure" whereas the pressure generated when a pressure producing
element moves from the second configuration to this first
configuration is termed "positive pressure". The pressure generated
by a single transition from one configuration to the other is
termed herein a pressure "pulse".
[0338] During set-up, the parameter P is typically given an initial
value equal to half of the number of pressure producing elements in
the array such as 10000 in the present example. The array is then
initialized such that each pressure producing element whose ordinal
number as determined by the LUT is less than P is brought to its
first configuration and the remaining pressure producing elements
are brought to their second configuration.
[0339] A suitable LUT (look up table), which has cells which
correspond one-to-one to the N pressure producing elements in the
array, storing integers from 1 to N, may be generated as
follows:
[0340] A criterion for LUT quality is first determined, which may
be application-specific. One suitable criterion for LUT quality is
now described.
[0341] A list is prepared of all possible subsets of consecutive
integers ranging between 1 and N. In the present example, the first
subset, termed hereinafter S2.sub.1, includes 2 integers: 1 and 2;
the second subset, S2.sub.2 includes the integers 2 and 3, and so
on for all subsets containing two integers. The last two-element
subset, S2.sub.1999, contains the integers 19999 and 20000. The
list also includes all possible three element subsets, namely, to
continue the example, S3.sub.1 (which includes integers 1, 2, 3),
S3.sub.2 (which includes integers 2, 3, 4), . . . S3.sub.19998
(which includes integers 19998, 19999, 20000). The list also
includes all 4 element subsets, 5 element subsets and so on and so
forth. The last subset, S20000.sub.1 contains all 20000 elements.
In general, a subset containing K integers, starting at i is
labeled SK.sub.i. It is appreciated that for a LUT containing N
cells, the number of possible subsets M equals M=(N-1)*N/2.
[0342] For each subset SK.sub.i, a set of coordinates is defined
(X.sub.i, Y.sub.i). (X.sub.i+1, Y.sub.i+1), . . . (X.sub.i+K-1,
Y.sub.i+K-1) such that the coordinates represent the position of
the pressure-producing elements whose ordinal numbers are i, i+1, .
. . i+k-1 according to the current LUT.
[0343] For each subset SK.sub.i a propagation angle .theta.K.sub.i
is computed e.g. using analytic or numeric computation methods,
typically using suitable computer simulation applications such as
Matlab, MatCAD or Mathematica. The sound waves' propagation angles
are computed for K coherent sound sources, disposed at positions
(X.sub.i, Y.sub.i), (X.sub.i+1, Y.sub.i+1), . . . (X.sub.i+K-1,
Y.sub.i+K-1), all producing sinusoidal waves at the same phase and
at a frequency equal to the system sampling rate, e.g. 44100
Hz.
[0344] A "propagation angle of a subset" is defined as follows:
Each subset corresponds to a subset of pressure producing elements.
A reference axis is defined passing through the center of mass of
the array of pressure producing elements and perpendicular to its
main surface. The intensity of sound generated by the subset of
pressure producing elements approaches a maximum as one retreats
from the array of pressure producing elements along the reference
axis. Therefore, a maximal intensity for the subset may be defined
by measuring the intensity at a location L which is on the
reference axis and sufficiently distant from the array so as to
ensure that the differences between the distance of location L and
each of the pressure producing elements in the subset are
sufficiently, e.g. an order of a magnitude, smaller than the
wavelength k associated with the system clock. At least one
reference plane is defined which includes the reference axis. It is
appreciated that an infinite number of such reference planes
exists. For cylindrical propagation applications in which a focal
axis is defined, select a reference plane which includes the focal
axis. It is appreciated that a LUT constructed on this basis would
typically also be suitable for omnidirectional applications. For
propagation applications in which a focal point is defined as
described herein, select a reference plane which includes the focal
point. If more than one such reference plane exists, select two
such reference planes which are mutually perpendicular.
[0345] The propagation angle of the subset, termed herein
.theta.K.sub.i, is defined for each reference plane selected for
that subset, as follows: Define an imaginary circle within the
reference plane whose center is at the point of intersection
between the reference axis and the main surface of the array and
whose radius is the distance between L and the main surface of the
array. Select two locations on the circumference of the circle on
both sides of the reference axis respectively, in which the sound
intensity generated by the subset of pressure producing elements is
half of the maximal intensity measured at L. The angle defined
between two radii connecting the center of the circle to these two
locations respectively is termed the propagation angle of the
subset for that reference plane. If the subset has two
perpendicular reference planes as described above, simple or
weighted average of the two propagation angles may be computed to
obtain a single propagation angle .theta.K.sub.i for the subset. If
the directivity pattern across a certain reference plane, e.g. a
vertical plane, is more important than that across the other,
perpendicular reference plane, greater weight is assigned to the
more important plane. For example, in certain applications the most
important consideration may be to prevent unwanted noise from
reaching locations on different floors in which case a vertical
reference plane would be more heavily weighted than the horizontal
reference plane.
[0346] An example of a suitable criterion for the "best-ness" of a
specific LUT is:
LUT.sub.score=1/[(average of all .theta.K.sub.i).times.(standard
deviation of all .theta.K.sub.i)]
[0347] To determine the most suitable LUT, one may use a computer
simulation to test and score all possible permutations i.e. all
possible N-cell LUTs, and selecting the best one thereof.
[0348] It is appreciated that the number of LUTs, each containing N
cells, is N! (N factorial). If N is sufficiently large, it becomes
impractical to test and evaluate all possible LUTs i.e. all
possible permutations of integers into LUT cells. If such is the
case, a smaller number of LUT permutations may be selected, e.g.
randomly, and the best one thereof is selected.
[0349] It is appreciated that alternatively, step 3200 may be
performed without resort to a fixed LUT stored during set-up.
Instead, the set of P.sub.t-P.sub.t-1 pressure producing elements
to be activated may be selected by selecting the best subset of
P.sub.t-P.sub.t-1 elements from among the set of pressure producing
elements which are currently in the second operative configuration.
This may be done by estimating the propagation angle .theta. for
each possible subset of P.sub.t-P.sub.t-1 elements and selecting
that subset which best matches the desired propagation pattern.
[0350] P.sub.t refers to the current value of P whereas P.sub.t-1
refers to the value of P in the previous system clock.
[0351] Furthermore, it is appreciated that in those applications in
which the directivity pattern is not important, any set of pressure
producing elements may be employed to achieve a temporal pressure
pattern dictated by the input signal.
[0352] Step 3300, in which the amount of delay with which to
operate each of the moving elements of moving element array 3010 or
3012 of FIGS. 20A-20B, is computed, determines the directionality
of the sound generated by the speaker. Preferred methods and
formulae for optionally positioning the moving element array as a
function of desired directionality of propagation, if possible, and
for computing delays also as a function of desired directionality
of propagation, are now described, for three example propagation
patterns termed herein omni-directional, cylindrical and
uni-directional. It is appreciated that the three propagation
patterns discussed particularly herewithin are discussed merely by
way of example.
[0353] FIGS. 22A-22B, taken together, describe a simplified example
of a solution for performing step 3300 when it is desired to
achieve omni-directional sound i.e. sound which propagates outward
through three dimensional space from a given point location termed
herein the "focal point" of the omni-directional sound.
Specifically, FIG. 22A is a simplified diagram of an
omni-directional propagation pattern having a focal point 3400 and
FIG. 22B is a diagram of a preferred positioning of a moving
element array relative to the focal point of the desired
omni-directional sound propagation pattern of FIG. 22A. In the
illustrated embodiment, the array of moving elements referenced
generally 3010 or 3012 in FIGS. 20A-20B comprises, merely by way of
example, a typically non-skewed array 3410 of 14.times.21 moving
elements. As shown, the array of moving elements is preferably
although not necessarily positioned, as illustrated in FIG. 22B,
such that its geometric center (located between the 7.sup.th and
8.sup.th rows, at the 11.sup.th column) of the array of moving
elements coincides with the focal point 3400 of the
omni-directional pattern, located at the center of the concentric
circles representing the omni-directional pattern as shown in FIG.
22A. The center of the array may also be positioned at the
projection of the focal point of the omni-directional pattern onto
the plane of the moving element array 3410. It is appreciated that
the array need not be positioned as illustrated and may instead be
positioned at any suitable location, such as a fixed location
independent of the particular propagation pattern currently
selected by a user.
[0354] It is appreciated that the array need not be of the
specified dimensions or shape. In fact preferred embodiments of
direct digital speakers are comprised of thousands to hundreds of
thousands of pressure-producing elements. The shape of the array
may change according to application and/or use.
[0355] It is also appreciated that the focal point referred to
herein need not be positioned on the main surface defined by the
array of pressure-producing elements. Changing the distance between
the focal point and the main surface of the array of the
pressure-producing elements changes the directionality pattern of
the device. E.g. placing the focal point on the surface (zero
distance) would produce true omni-directional directivity pattern
where sounds intensity remain essentially equal regardless of the
angle in which the sound propagates. Placing the focal point at a
certain distance, d behind the surface of pressure-producing
elements defines a projection cone (in the case of a round array)
or a projection pyramid (in the case of a square or rectangular
array) that is characterized by a head angle narrower than 180
degrees. Placing the focal point at an infinite distance behind the
main surface of the pressure producing elements (given that the
sound produced by the pressure producing elements is produced in
front of the main surface) typically defines a projection cone or a
projection pyramid that is very narrow and would produce a true
unidirectional directivity pattern. Typically, the sound intensity
throughout the projection cone or projection pyramid remains
essentially equal while the intensity outside the cone or pyramid
is significantly lower. It is appreciated that d may be either 0 or
infinity in certain applications. In certain applications, d may be
determined as a function of a user control.
[0356] FIG. 23 is a simplified pictorial illustration of speaker
apparatus constructed and operative in accordance with FIGS.
20A-22B and operative, e.g. by virtue of having been so programmed,
to generate omni-directional sound which is particularly suitable
for the environment illustrated in FIG. 23 in which consumers of
the sound entirely surround the speaker, typically at more than one
levels including a ground level and a first floor level as
shown.
[0357] For applications in which a pre-determined and fixed focal
point of omni-directional sound propagation is known, e.g. in a
conventional planetarium, circus arena or circular auditorium, the
array of moving elements provided in accordance with certain
embodiments of the present invention is preferably although not
necessarily positioned such that the array's center coincides with
the desired focal point of the desired omni-directional propagation
pattern as described above with reference to FIGS. 22A-22B. It is
appreciated, however, that although it is preferable to position
the array of moving elements such that its center is disposed as
close as possible to a currently desired e.g. user-selected focal
point of a currently desired e.g. user selected omni-directional
propagation pattern, nonetheless, embodiments of the invention
shown and described herein allow omni-directional propagation from
a wide variety of foci to be achieved using an array of moving
elements which may be stationary and need not be centered at the
focal point of the omni-directional directivity pattern.
[0358] Referring back to FIG. 22A, each circle shown represents
half a phase and has a radius r which is computed using the
following formula:
r=(Nd.lamda./2+N.sup.2.lamda./4).sup.0.5
where:
[0359] N=the serial number of the circle, counting outward from the
center and starting from 1,
[0360] d=the distance of the plane of the non-skewed array from the
focal point of the omni-directional sound
[0361] .lamda.=c T, where c=the speed of sound through the medium
in which the speaker is operating, typically air, and T=the period
of the system clock of FIG. 20A or 20B (not shown).
[0362] It is appreciated that specific delay values for the moving
elements in array 3410, suitable for achieving the omni-directional
pattern of FIG. 22A, may be determined as follows:
[0363] (a) Any moving element which coincides with a circle whose
serial number is N is assigned a delay value of N T/2.
[0364] (b) Any moving element which does not coincide with a
circle, and instead falls between a pair of circles whose serial
numbers are N and N+1 is assigned a delay value by interpolating
e.g. linearly between the following two values: NT/2 and
(N+1)T/2.
[0365] Alternatively, a suitable formula for determining delays is
described in detail below.
[0366] FIG. 24 is a diagram of a cylindrical pattern of sound
directivity which it is achievable using an embodiment of the
apparatus of the present invention. As shown, at each point along
the sound propagates, in the plane, omni-directionally and
identically from each point along a given focal axis 3510.
[0367] FIG. 25 is a diagram showing one preferred positioning of
the moving element array 3010, shown to be rectangular by way of
example, relative to the cylindrical pattern of sound directivity
shown in FIG. 24. If possible, the moving element array is
preferably disposed symmetrically about the focal axis such that,
as shown, its sides are respectively perpendicular to or parallel
to the focal axis, or, less preferably and as illustrated, the
moving element array is preferably disposed symmetrically about the
projection of the focal axis upon the plane defined by the array.
It is appreciated that the particular positionings described herein
and illustrated need not be provided and alternatively, the moving
element array may be disposed and oriented in any suitable,
application-dictated location.
[0368] FIG. 26 is an isometric view of the moving element array
3010 or 3012 of FIGS. 20A-20B, showing uni-directional sound
generated by that moving array and propagating in a desired or
predetermined direction a as indicated by arrows.
[0369] FIG. 27 is a pictorial illustration of a preferred
application for speaker apparatus 3600 constructed and operative in
accordance with the present invention, being constructed e.g.
programmed to generate uni-directional sound in at least one
typically user-selected direction. In the embodiment of FIG. 27,
either or both of two uni-directional sounds streams 3610 and 3620
are generated to serve listeners located at positions 3630 and 3640
respectively.
[0370] If the array of moving elements is a rectangle 3650 having
first and second internally parallel and mutually perpendicular
pairs of sides, then the array is typically oriented such that the
projection of the desired direction of propagation onto the plane
of the array, which may be vertical as shown in FIG. 27, is
parallel to one of the pairs of sides and hence perpendicular to
the other pair of sides as shown in FIG. 26. In this case, the
delay of each moving element in the array may be the product of cos
alpha (where alpha is the angle of propagation as shown in FIG. 22)
and the distance x of that moving element from a selected one of
the pair of perpendicular sides.
[0371] As suggested by FIG. 27, it may be desired to produce two
sound streams to be perceived exclusively and simultaneously by
listeners positioned in two respective azimuthal positions relative
to the speaker, is now described. According to this embodiment,
some of the moving elements in the array are devoted to producing
the first sound stream, and the remaining elements in the array are
devoted to producing the second sound. The delays used for each
moving element are determined as described above in the
uni-directional case. It is appreciated that more generally, any
suitable number of sound streams rather than just two sound streams
may be produced.
[0372] The uni-directional embodiment illustrated in FIG. 26 or 27
has a wide variety of applications, such as but not limited to (a)
entertainment content providers, such as television, computer,
music player or radio, including a programmable directional speaker
operative to send uni-directional sound exclusively to one or more
user-selected directions. Different content, such as a plurality of
language versions corresponding to a single visual content item,
can be sent simultaneously to a plurality of user-selected
directions, thereby to enable a group of friends or family members
to share a viewing experience but to simultaneously and exclusively
receive individualized audio content, e.g. to each in his own
language, corresponding to the viewing experience; and (b)
Sound-producing toys including a sensor operative to monitor the
azimuthal and elevational position of the child relative to the toy
and a directional speaker operative to send uni-directional sound
exclusively toward the child in a direction which corresponds to
the child's current azimuthal and elevational position relative to
the toy.
[0373] Generally, a suitable formula for determining a suitable
amount of delay for each moving element, for omni-directional sound
propagation, is as follows:
delay=[(d.sup.2+r.sup.2).sup.0.5-d]/c
[0374] where
[0375] r=distance between the projection of the focal point onto
the moving elements array
plane and a given moving element,
[0376] d=the distance of the plane of the array of the moving
elements from the focal point of the omni-directional sound
[0377] c=the speed of sound through the medium in which the speaker
is operating, typically air.
[0378] For cylindrical sound propagation, the same formula may be
employed, however d is now defined as the distance of the plane of
the array of moving elements from the focal axis which is typically
parallel thereto
[0379] For unidirectional sound propagation, as described above,
the formula employed may be
[0380] delay=x cos .alpha.
[0381] where:
[0382] x=the distance from the moving elements array edge plane and
a given moving element and
[0383] .alpha.=the angle between direction and moving elements
array plane.
[0384] It is appreciated that the embodiments shown and described
herein generate sound propagation patterns which well approximate
desired patterns such as omni-directional, cylindrical, and uni-,
bi- or even multi-directional patterns. However, at least due to
the finite size of the array of moving elements, the actual sound
propagation pattern is never exactly identical to the theoretically
desired propagation pattern. Generally, the theoretically desired
propagation pattern is better achieved at locations which are close
to the moving element array, than at locations which are further
from the moving element array.
[0385] It is also appreciated that the larger the array (both in
terms of number of pressure-producing elements and in terms of
dimensions), the more closely the desired propagation pattern is
achieved.
[0386] A particular feature of certain embodiments of the present
invention is that a single speaker including one or more
pressure-producing element arrays which arrays may be fixed, can be
programmed to generate a plurality of directivity patterns
differing in parameterization or even in shape.
[0387] It is appreciated that a multi-unidirectional propagation
pattern may be provided, in which the user can, if desired, select
the number of and/or direction and/or other characteristics of more
than one uni-directional beams. The uni-directional embodiment is
described herein and generalization of the uni-directional
embodiment described herein to a multi-unidirectional embodiment
may be achieved using techniques known in the art such as
techniques used to define the direction, number of, and/or other
characteristics of beam/s produced by multi-beam phased array
applications e.g. RADAR beams. More generally, it is appreciated
that a combination of propagation patterns may be provided, in
which the user can, if desired, select the number of and/or
direction and/or other characteristics of more than one component
propagation patterns each of which may comprise any suitable
pattern such as but not limited to a uni-directional pattern,
omni-directional pattern, cylindrical pattern, or any combination
thereof. Several propagation patterns are described herein and
combination thereof may be achieved using techniques known in the
art such as techniques used to define the direction, number of,
and/or other characteristics of beam/s produced by multi-beam
phased array applications e.g. RADAR beams
[0388] It is appreciated that the array of moving elements need not
be planar as illustrated and that alternatively the teachings of
the present invention may be appropriately modified to accommodate
a non-planar array of moving elements.
[0389] FIG. 28 is a simplified pictorial illustration of a
non-rectangular array of moving elements. According to one
embodiment of the present invention, delays for moving elements in
non-rectangular arrays may be computed by circumscribing the
non-rectangular array in a rectangular array and proceeding to
compute delays as described herein, for the circumscribing
rectangular array. Each moving element in the non-rectangular array
is assigned a delay value which equals the delay value computed by
this process, i.e. according to its position in the (imaginary)
circumscribing rectangular array.
[0390] If the array of moving elements is not rectangular, the
following rules may be employed to position the array although
alternatively the invention may accommodate an array of moving
elements positioned arbitrarily:
[0391] i. If omni-directional propagation is desired and the
designer is entirely free to position the array, the array may be
positioned such that the center of mass of the non-rectangular
array coincides with the focal point of the omni-directional
propagation. Preferably and more generally, the array may be
positioned such that the center of mass of the non-rectangular
array is as close as possible to the focal point of the
omni-directional propagation
[0392] ii. If cylindrical propagation is desired and the designer
is entirely free to position the array, the array may be positioned
such that an axis of mass 3700 of the non-rectangular array 3710,
partitioning the array into two sub-arrays 3720 and 3730 of equal
area as shown in FIG. 28 is disposed along the focal axis of the
cylindrical propagation. If several axes of mass exist, the longest
such axis is typically selected. Preferably and more generally, the
array may be positioned such that an axis of mass, preferably the
longest available, of the non-rectangular array is disposed
parallel to the focal axis of the cylindrical propagation.
[0393] iii. If uni-directional propagation is desired and the
designer is free to position the array, the array may be positioned
such that the desired propagation direction is close to
perpendicular to the main surface of the array.
[0394] The scope of the present invention includes but is not
limited to a method for controlling direct digital speaker
apparatus receiving a digital input signal and generating sound
accordingly, the method comprising providing an array of
pressure-producing elements, and computing a timing pattern
determining if and when each pressure-producing element is
operative to produce pressure pulses so as to achieve a desired
directivity pattern. The array is then operated in accordance with
the timing pattern in order to achieve sound having the desired
directivity pattern.
[0395] Optionally, the providing and computing steps are performed
a plurality of times thereby to obtain a corresponding plurality of
arrays and a corresponding plurality of timing patterns defining a
corresponding plurality of directivity patterns. The method then
also comprises the step of operating the plurality of arrays
simultaneously in accordance with the corresponding plurality of
timing patterns respectively thereby to obtain a single directivity
pattern comprising a combination of the directivity patterns
corresponding to the plurality of timing patterns. The plurality of
arrays may in fact comprise portions of a single larger array. So,
for example, a single array of pressure producing elements such as
any of those shown and described herein may be partitioned into
regions, e.g. quarters, and the pressure producing elements in each
region may be operated in accordance with its own particular timing
pattern or delay pattern. For example, this allows a pattern of
several, say four, different unidirectional beams to be achieved.
Alternatively, to give another example, this allows, say,
omnidirectional background sound to be superimposed on one or more
different foreground sound streams each respectively having its
own, say, uni-directional, cylindrical or omni-directional
propagation pattern. It is appreciated that in multi-directional
embodiments, each said unidirectional beam may produce a different
digital input signal, e.g. the left and right channels of a
stereophonic signal.
[0396] It is appreciated that the electromagnetic field controller
30 is preferably designed to ensure that the alternating current
flowing through the coil maintains appropriate magnetic field
strength at all times and under all conditions so as to allow
sufficient proximity between the moving elements 10 and the
electrostatic latches 20 to enable latching, while preventing the
moving elements 10 from moving too fast and damaging themselves or
the latches 20 as a result of impact.
[0397] With specific reference to the Figures, it is stressed that
the particulars shown are by way of example and for purposes of
illustrative discussion of the preferred embodiments of the present
invention only, and are presented in the cause of providing what is
believed to be the most useful and readily understood description
of the principles and conceptual aspects of the invention. In this
regard, no attempt is made to show structural details of the
invention in more detail than is necessary for a fundamental
understanding of the invention. The description taken with the
drawings makes apparent to those skilled in the art how the several
forms of the invention may be embodied in practice.
[0398] Features of the present invention which are described in the
context of separate embodiments may also be provided in combination
in a single embodiment. Conversely, features of the invention which
are described for brevity in the context of a single embodiment may
be provided separately or in any suitable subcombination. For
example, moving elements may be free floating, or may be mounted on
filament-like flexures or may have a surrounding portion formed of
a flexible material. Independently of this, the apparatus may or
may not be configured to reduce air leakage therethrough as
described above. Independently of all this, the moving element may
for example comprise a conductor, coil, ring- or disc-shaped
permanent magnet, or ring- or disc-shaped ferromagnet and the
magnets, if provided, may or may not be arranged such that the
poles of some e.g. 50% thereof are oppositely disposed to the poles
of the remaining e.g. 50% of the magnets. Independently of all
this, the latch shape may, in cross-section, be solid, annular,
perforated with or without a large central portion, or notched or
have any other suitable configuration. Independently of all this,
control of latches may be individual or by groups or any
combination thereof. Independently of all this, there may be one or
more arrays of actuator elements which each may or may not be
skewed and the cross-section of each actuator element may be
circular, square, triangular, hexagonal or any other suitable
shape.
[0399] The present invention has been described with a certain
degree of particularity, but those versed in the art will readily
appreciate that various alterations and modifications may be
carried out to include the scope of the following Claims:
* * * * *