U.S. patent application number 12/173696 was filed with the patent office on 2010-01-21 for unimorph/bimorph piezoelectric package.
Invention is credited to Wesley T. Horth, Grace R. Kessenich, Baruch Pletner.
Application Number | 20100013352 12/173696 |
Document ID | / |
Family ID | 41529700 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100013352 |
Kind Code |
A1 |
Pletner; Baruch ; et
al. |
January 21, 2010 |
UNIMORPH/BIMORPH PIEZOELECTRIC PACKAGE
Abstract
A piezoelectric package comprises an upper and lower
piezoelectric plates, each having opposing electrodes. The
piezoelectric package further comprises an electrically insulative
structure encapsulating the piezoelectric plates. The piezoelectric
package further comprises first and second external connectors
mounted to the insulative structure. The connectors respectively
have connector terminals that are electrically coupled to the
electrodes in different orders, and have geometric arrangements
that are identical, such that a single interface device can be
selectively mated to either of the connectors. The piezoelectric
package may be incorporated into a system that comprises electronic
circuitry configured for operating the piezoelectric package, and a
single interface device electrically coupled between the electronic
circuitry and either of the external connectors of the
piezoelectric package to selectively configure the package between
a unimorph and a bimorph.
Inventors: |
Pletner; Baruch; (Newton,
MA) ; Kessenich; Grace R.; (Somerville, MA) ;
Horth; Wesley T.; (Dalton, MA) |
Correspondence
Address: |
Michael J. Bolan;Vista IP Law Group LLP
9th Floor, 2040 Main Street
Irvine
CA
92614
US
|
Family ID: |
41529700 |
Appl. No.: |
12/173696 |
Filed: |
July 15, 2008 |
Current U.S.
Class: |
310/316.01 ;
29/25.35; 310/348 |
Current CPC
Class: |
H01L 41/23 20130101;
H01L 41/0926 20130101; H01L 41/0973 20130101; Y10T 29/42 20150115;
H01L 41/0475 20130101; H01L 41/312 20130101; F16F 15/005
20130101 |
Class at
Publication: |
310/316.01 ;
310/348; 29/25.35 |
International
Class: |
H02N 2/06 20060101
H02N002/06; H01L 41/053 20060101 H01L041/053; H01L 41/22 20060101
H01L041/22 |
Claims
1. A piezoelectric package, comprising: an upper piezoelectric
plate having opposing top and bottom electrodes; a lower
piezoelectric plate having opposing top and bottom electrodes; an
electrically insulative structure encapsulating the piezoelectric
plates; a first external connector mounted to the insulative
structure, the first connector having first connector terminals
electrically coupled to the electrodes in a first order; and a
second external connector mounted to the insulative structure, the
second connector having second connector terminals electrically
coupled to the electrodes in a second order different from the
first order, wherein the geometric arrangement of the first
connector terminals are identical to the geometric arrangement of
the second connector terminals, such that a single interface device
can be selectively mated to either of the connectors.
2. The piezoelectric package of claim 1, wherein the insulative
structure forms a board.
3. The piezoelectric package of claim 1, wherein the insulative
structure is composed of a rigid material.
4. The piezoelectric package of claim 1, wherein: the first
connector terminals comprise four connector terminals, a first of
which is electrically coupled to the bottom electrode of the lower
piezoelectric plate, a second of which is electrically coupled to
the top electrode of the lower piezoelectric plate, a third of
which is electrically coupled to the bottom electrode of the upper
piezoelectric plate, and a fourth of which is electrically coupled
to the top electrode of the upper piezoelectric plate; and the
second connector terminals comprise four connector terminals, a
first of which is electrically coupled to the bottom electrode of
the lower piezoelectric plate, a second of which is electrically
coupled to the top electrode of the lower piezoelectric plate, a
third of which is electrically coupled to the top electrode of the
upper piezoelectric plate, and a fourth of which is electrically
coupled to the bottom electrode of the upper piezoelectric
plate.
5. The piezoelectric package of claim 1, further comprising
electrical conductors encapsulated within the insulative structure,
wherein the electrical conductors are respectively coupled between
the electrodes and the connector terminals.
6. The piezoelectric package of claim 5, further comprising first
external terminals and second external terminals disposed on the
insulative structure, wherein the first external terminals are
electrically coupled respectively between the electrical conductors
and the first connector terminals, and the second external
terminals are electrically coupled respectively between the
electrical conductors and the second connector terminals.
7. The piezoelectric package of claim 6, wherein the electrodes
extend within respective parallel planes, wherein each of the
electrical conductors comprises an electrically conductive trace
and an electrically conductive via, the electrically conductive
trace extending within insulative structure in a direction parallel
to the planes, and the via extending within the insulative
structure in a direction perpendicular to the planes.
8. The piezoelectric package of claim 7, wherein the first external
terminals are electrically coupled respectively to the vias in a
first order, and the second external terminals are electrically
coupled to the vias in a second order different from the first
order, wherein the geometric arrangement of the first external
terminals is identical to the geometric arrangement of the second
external terminals.
9. The piezoelectric package of claim 7, wherein each of the vias
is a blind via.
10. The piezoelectric package of claim 1, wherein the single
interface device is a cable.
11. The piezoelectric package of claim 1, wherein the single
interface device is a wireless transmitter/receiver.
12. A system, comprising: the piezoelectric package of claim 1;
electronic circuitry electrically coupled to the piezoelectric
package, the electronic circuitry configured for sensing and/or
actuating vibrations via the piezoelectric package; and an
interface device configured for mating between the electronic
circuitry and either of the first and second connectors.
13. The system of claim 12, wherein the piezoelectric package has a
unimorph configuration when the cable is mated between the
electronic circuitry and the first connector, and a bimorph
configuration when the cable is mated between the electronic
circuitry and the second connector.
14. A system, comprising: a piezoelectric package including upper
and lower piezoelectric plates and first and second external
connectors, each of the external connectors being electrically
coupled to the piezoelectric plates; electronic circuitry
configured for sensing and/or actuating vibrations via the
piezoelectric package; a single interface device electrically
coupled between the electronic circuitry and the piezoelectric
package, wherein the single interface device is configured for
being selectively mated to either of the first and second external
connectors, wherein the piezoelectric package is in a unimorph
configuration when the single interface device is mated to the
first external connector, and the piezoelectric package is in the
bimorph configuration when the single interface device is mated to
the second external connector.
15. The system of claim 14, wherein the piezoelectric package takes
the form of a printed circuit board.
16. The system of claim 14, further comprising a host structure to
which the piezoelectric package is mounted, wherein the electronic
circuitry is electrically coupled to the piezoelectric package, the
electronic circuitry configured for sensing and/or actuating
vibrations within the host structure via the piezoelectric
package.
17. The system of claim 14, wherein the single interface device is
a cable.
18. The system of claim 14, wherein the single interface device is
a wireless transmitter/receiver.
19. A method of making the piezoelectric package of claim 7,
comprising: locating the upper and lower piezoelectric plates
adjacent each other; forming the electrically conductive traces
respectively on at least some of a plurality of electrically
insulative sheets; electrically coupling the traces respectively to
the electrodes; bonding the insulative sheets to each other to form
the insulative structure; disposing the electrically conductive
vias within the insulative sheets, wherein the vias and traces are
electrically coupled respectively to each other; and electrically
coupling the first connector terminals of the first external
connector respectively to the vias in the first order; and
electrically coupling the second connector terminals of the second
external connector respectively to the vias in the second
order.
20. The method of claim 19, wherein bonding the insulative sheets
comprises applying heat to the insulative sheets to transform the
piezoelectric package into an integrated composite structure.
21. The method of claim 19, further comprising: forming the first
external terminals and the second external terminals on one of the
insulative sheets; forming first electrically conductive traces and
second electrically conductive traces on the one insulative sheet,
the first traces electrically coupled respectively between the vias
and the first external terminals, and the second traces
electrically coupled respectively between the vias and the second
external terminals; bonding the one electrically insulative sheet
to another one of the insulative sheets; electrically coupling the
first connector terminals respectively to the first external
terminals; and electrically coupling the second connector terminals
respectively to the second external terminals.
22. The method of claim 19, further comprising disposing at least
one of the insulative sheets between the piezoelectric plates,
thereby electrically isolating the bottom electrode of the upper
piezoelectric plate from the top electrode of the lower
piezoelectric plate.
23. The method of claim 19, wherein the insulative sheets have
windows, the method further comprising: aligning the windows; and
disposing the piezoelectric elements within the windows.
24. The method of claim 19, wherein the single interface device is
a cable.
25. The method of claim 19, wherein the single interface device is
a wireless transmitter/receiver.
Description
RELATED APPLICATIONS
[0001] This application is filed concurrently with U.S. patent
application Ser. No. 12/______, (VIP Docket No. IPT-008(2)),
entitled "Scalable Piezoelectric Package," the disclosure of which
is expressly incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present inventions generally relate to devices for
sensing and suppressing vibrations, and in particular, to
piezoelectric sensors and actuators for use on equipment.
BACKGROUND OF THE INVENTION
[0003] Structural vibration is one of the key performance limiting
phenomena in many types of advanced machinery, such as space launch
vehicle shrouds, all types of jet and turbine engines, robots, and
many types of manufacturing equipment. Because structural vibration
depends on many factors that are not easily modeled, such as
boundary and continuity conditions, as well as the disturbance
environment, it is impossible to design a machine from the first
prototype that will meet all vibration requirements. This means
that the final steps in analyzing and suppressing vibration are
accomplished after the actual production unit has been
completed.
[0004] To address this shortfall, it is known to incorporate
vibration analysis and suppression systems into equipment. In
general, a typical vibration analysis and suppression system
includes a multitude of vibration sensors and vibration actuators
that are installed on-board the equipment in selected locations.
The system also includes a control system that transmits control
signals in accordance with a vibration suppression algorithm to the
actuators during normal operation of the equipment to mechanically
suppress the vibrations. Using a feedback loop, the sensed
vibration information is fed back to the control circuitry, which
adjusts the control signals in response to dynamic conditions.
[0005] It is also known to incorporate vibration analysis devices
into equipment for the purpose of performing non-destructive
testing (i.e., testing that does not destroy the equipment). For
example, sensors can be incorporated into aircraft to measure flow
and combustion induced vibrations in turbines or combustion
housings of propulsion systems, can be incorporated pre-forms,
concrete and other structures that require cure-monitoring, or can
be incorporated into equipment to monitor damage (e.g.,
delamination) that may present as a change in vibration
characteristics.
[0006] Significant to the present invention, piezoelectric sensors
and actuators are utilized extensively to detect and/or suppress
vibrations in equipment. Such piezoelectric devices can be
incorporated into the host structure of the equipment as plates
that can be embedded within the host structure or externally
applied to the host structure as patches. When used as a sensor, a
piezoelectric plate contracts and expands along a plane parallel to
the surface of the plate (in the x- and y-direction) in response to
vibrations induced within the piezoelectric plate via the host
structure, which in turn, induces an electrical field in a plane
perpendicular to the surface of the plate (in the z-direction),
creating a voltage potential between the top and bottom surfaces of
the piezoelectric plate. In a similar manner, when used as an
actuator, a piezoelectric plate contracts and expands along a plane
parallel to the surface of the plate (in the x- and y-direction) in
response to a voltage potential between the top and bottom surfaces
of the piezoelectric plate that induces an electrical field induced
in a plane perpendicular to the surface of the plate (in the
z-direction), which in turn, induces a vibration in the host
structure. Whether used as a sensor or an actuator, the magnitude
of the voltage potential on the top and bottom surfaces of the
piezoelectric plate will be proportional to the magnitude of the
contraction/expansion of the piezoelectric plate, and thus, the
vibrations of the host structure. Thus, the nature of the
vibrations sensed within the host structure can be determined via
analysis of the voltage potential, and the nature of the vibrations
induced within the host structure can be controlled via the voltage
potential applied to the piezoelectric plate.
[0007] To protect the very fragile piezoelectric plate from damage,
and to functionally couple the piezoelectric plate between the host
structure and the external circuitry that senses vibrations from
the host structure and/or induces vibrations within the host
structure, it is necessary to incorporate the piezoelectric plate
into a package. Such packages typically include a pair of wire
leads respectively coupled to the top and bottom surfaces of the
piezoelectric plate to convey the voltage potential to and/or from
the piezoelectric plate, and one or more layers of an electrically
insulating material that encapsulate the piezoelectric plate to not
only protect it from damage that might otherwise occur when dropped
or mishandled, but also to electrically insulate the piezoelectric
plate and wire leads from the host structure. A connector is
typically mounted to the piezoelectric package, so that a cable
from the control/sensing circuit can be operably coupled to the
piezoelectric plate.
[0008] Piezoelectric packages are generally supplied to a user in a
one size. Thus, if a single piezoelectric package is insufficient
for providing the desired actuation or sensing functions at a
particular location of the host structure, it may be desirable to
locate multiple piezoelectric packages at this location. In this
case, however, multiple cables must be connected between the
control/sensing circuit and the respective connectors of the
piezoelectric packages, even though the multiple packages function
as a single actuator/sensor. In other words, the actuation/sensing
function at a particular location of a host structure may not be
easily scalable.
[0009] Oftentimes, a pair of upper and lower piezoelectric plates
are incorporated into the piezoelectric package, which allows the
package, when used as either an actuator or a sensor, to be
operated in a specific morphological configuration, and in
particular, in either a unimorph (or extensional) configuration or
in a bimorph (or bending) configuration.
[0010] In a unimorph configuration, the piezoelectric plates both
expand or both contract when signals of the same polarity are
transmitted to the respective piezoelectric plates (assuming the
package is operated as an actuator), and signals of the same
polarity are received from the respective piezoelectric plates when
the piezoelectric plates both expand or both contract (assuming the
package is operated as a sensor). The piezoelectric package can be
configured as a unimorph by coupling leads of the same polarity to
the same polarized sides of the respective piezoelectric plates
(e.g., positive leads to the positively polarized sides of the
piezoelectric plates, and negative leads to the negatively
polarized sides of the piezoelectric plates).
[0011] In contrast, in a bimorph configuration, one piezoelectric
plate expands while the other piezoelectric plate contracts when
signals of the same polarity are transmitted to the respective
piezoelectric plates (assuming the package is operated as an
actuator), and signals of the same polarity are received from the
respective piezoelectric plates when one piezoelectric plate
expands while the other piezoelectric plate contracts (assuming the
package is operated as a sensor). The piezoelectric package can be
configured as a bimorph by coupling leads of the opposite polarity
to the same polarized sides of the respective piezoelectric plates
(e.g., one positive lead and one negative lead respectively to the
positively polarized and negatively polarized sides of one
piezoelectric plate, and the other positive lead and the other
negative lead respectively to the negatively polarized and
positively polarized sides of the other piezoelectric plate).
[0012] When mounting the piezoelectric package to or within host
structure, it is desirable that the stresses exerted by the upper
and lower piezoelectric plates combine in a manner that maximizes
the strain applied to the host structure when the package is
operated as an actuator, or combine in a manner that maximizes the
magnitude of combination of the signals received from the upper and
lower piezoelectric plates when the package is operated as a
sensor. This result can be achieved by judiciously selecting the
morphological configuration of the piezoelectric package.
[0013] In particular, the relationship between the piezoelectric
package and the host structure to which it is installed will often
depend on the location of the package relative to the neutral axis
of the structure to which the package is mounted. That is, any
structure undergoing bending has a neutral axis plane--a plane on
which no bending stress is experienced. The location of the neutral
axis depends on the boundary conditions, material, and geometry of
the structure, among other factors. On one side of this plane, the
structure expands and on the other side, it contracts. If the
piezoelectric package is located entirely on one side of the
neutral axis, a unimorph configuration is better, as both
piezoelectric plates will simultaneously expand or simultaneously
contract in accordance with the side of the neutral axis on which
it resides and the bending direction of the neutral axis. If the
neutral axis extends through the piezoelectric package, however, a
bimorph configuration is likely better (though it actually depends
on the exact location within the piezoelectric package), as one
piezoelectric plate will expand while the other piezoelectric plate
will contract in accordance the bending direction of the neutral
axis.
[0014] It can be appreciated that dynamic selection of a unimorph
or bimorph configuration allows the user to select the most
sensitive configuration in the case where the piezoelectric package
is used as a sensor, or the most vibratory configuration in the
case where the piezoelectric package is used as an actuator. To
enable the dynamic selection of the morphological configuration,
the leads, which are respectively disposed along vertical planes to
connect to the top and bottom sides of both piezoelectric plates,
can be laterally extended out from the piezoelectric package to
form two sets of terminals (which may, e.g., be configured in a
stair step fashion). Two connectors can then be respectively
coupled to the terminal sets, so that a cable can be connected to
the appropriate connector to dynamically place the piezoelectric
package in the desired morphological configuration.
[0015] Because the relative orientation of the leads are vertically
fixed, however, it is difficult to orient the respective terminal
sets differently in order to enable selectivity between the
unimorph and bimorph configurations using identical connectors.
While it is theoretically possible to reconfigure the output/input
signals at the interface of the control/sensing circuit, in
practice, this would require that the device in which the
control/sensing circuit is contained be modified to simultaneously
input and/or output two signals, and would further require such
device to be modified to allow dynamic selection between a unimorph
configuration and a bimorph configuration. However, most existing
devices designed to operate with piezoelectric packages are only
capable of inputting or outputting a single signal. Thus, in this
case, different connector configurations must be used in order to
enable dynamic selectivity between unimorph and bimorph
configuration. As a result, two different cables must be used with
the piezoelectric package--one that uniquely couples to the
unimorph connector and one that uniquely couples to the bimorph
connector. Thus, the proper cable corresponding to the desired
morphological configuration must be selected, which may become
quite tedious, especially when multiple piezoelectric packages are
to be mounted to the host structure.
[0016] Thus, there remains a need to provide a scalable and easily
manufacturable piezoelectric package whose morphological
configuration can be dynamically changed in a more convenient
manner.
SUMMARY OF THE INVENTION
[0017] In accordance with a first aspect of the present inventions,
a piezoelectric package is provided. The piezoelectric package
comprises an upper piezoelectric plate having opposing top and
bottom electrodes, and a lower piezoelectric plate having opposing
top and bottom electrodes. The piezoelectric package further
comprises an electrically insulative structure encapsulating the
piezoelectric plates. As one example, the insulative structure may
form a rigid board.
[0018] The piezoelectric package further comprises first and second
external connectors mounted to the insulative structure.
Significantly, the first and second connectors respectively have
first and second connector terminals that are electrically coupled
to the electrodes in different orders, and have geometric
arrangements that are identical, such that a single interface
device (e.g., a cable or a wireless transmitter/receiver) can be
selectively mated to either of the connectors.
[0019] For example, the first connector terminals may comprise four
connector terminals, a first of which is electrically coupled to
the bottom electrode of the lower piezoelectric plate, a second of
which is electrically coupled to the top electrode of the lower
piezoelectric plate, a third of which is electrically coupled to
the bottom electrode of the upper piezoelectric plate, and a fourth
of which is electrically coupled to the top electrode of the upper
piezoelectric plate. In contrast, the second connector terminals
may comprise four connector terminals, a first of which is
electrically coupled to the bottom electrode of the lower
piezoelectric plate, a second of which is electrically coupled to
the top electrode of the lower piezoelectric plate, a third of
which is electrically coupled to the top electrode of the upper
piezoelectric plate, and a fourth of which is electrically coupled
to the bottom electrode of the upper piezoelectric plate.
[0020] In one embodiment, the piezoelectric package further
comprises electrical conductors encapsulated within the insulative
structure, and respectively coupled between the electrodes and the
connector terminals. The piezoelectric package may further comprise
first and second external terminals disposed on the insulative
structure. The first external terminals are electrically coupled
respectively between the electrical conductors and the first
connector terminals, and the second external terminals are
electrically coupled respectively between the electrical conductors
and the second connector terminals.
[0021] If the electrodes extend within respective parallel planes,
each of the electrical conductors may comprise an electrically
conductive trace and an electrically conductive via (e.g., a blind
via), with the electrically conductive trace extending within
insulative structure in a direction parallel to the planes, and the
via extending within the insulative structure in a direction
perpendicular to the planes. In this case, the first and second
external terminals may be electrically coupled respectively to the
vias in different orders, and the geometric arrangements of the
first and second external terminals may be identical, so that
identical external connectors can be mounted to the insulative
structure.
[0022] The piezoelectric package may be incorporated into a system
that includes electronic circuitry electrically coupled to the
piezoelectric package, and configured for sensing and/or actuating
vibrations via the piezoelectric package, and an interface device
(e.g., a cable or a wireless transmitter/receiver) configured for
mating between the electronic circuitry and either of the first and
second connectors. In this case, the piezoelectric package may have
a unimorph configuration when the interface device is mated between
the electronic circuitry and the first connector, and a bimorph
configuration when the interface device is mated between the
electronic circuitry and the second connector.
[0023] In accordance with a second aspect of the present invention,
a system is provided. The system comprises a piezoelectric package
(e.g., a printed circuit board) including upper and lower
piezoelectric plates and first and second external connectors, with
each of the external connectors being electrically coupled to the
piezoelectric plates. The system further comprises electronic
circuitry configured for sensing and/or actuating vibrations via
the piezoelectric package. The system may further comprise a host
structure to which the piezoelectric package is mounted. In this
case, the electronic circuitry is electrically coupled to the
piezoelectric package, and is configured for sensing and/or
actuating vibrations within the host structure via the
piezoelectric package.
[0024] The system further comprises a single interface device
(e.g., a cable or a wireless transmitter/receiver) electrically
coupled between the electronic circuitry and the piezoelectric
package. The single interface device is configured for being
selectively mated to either of the external connectors, such that
the piezoelectric package is in a unimorph configuration when the
interface device is mated to the first external connector, and the
piezoelectric package is in the bimorph configuration when the
interface device is mated to the second external connector.
[0025] In accordance with a third aspect of the present inventions,
a method of making a piezoelectric package is provided. The method
comprises locating upper and lower piezoelectric plates (each
having opposing top and bottom electrodes) adjacent each other. The
method further comprises forming electrically conductive traces
respectively on at least some of a plurality of electrically
insulative sheets, electrically coupling the traces respectively to
the electrodes, and bonding the insulative sheets to each other
(e.g., by applying heat to the insulative sheets to transform the
piezoelectric package into an integrated composite structure). The
method may optionally comprise disposing at least one of the
insulative sheets between the piezoelectric plates, thereby
electrically isolating the bottom electrode of the upper
piezoelectric plate from the top electrode of the lower
piezoelectric plate. The method may also optionally comprise
aligning windows within the insulative sheets, and disposing the
piezoelectric elements within the windows.
[0026] The method further comprises disposing electrically
conductive vias within the insulative sheets and electrically
coupled to the traces. The method further comprises electrically
coupling first connector terminals of a first external connector
respectively to the vias in a first order, and electrically
coupling second connector terminals of a second external connector
respectively to the vias in a second order different from the first
order. The geometric arrangements of the first and second connector
terminals are identical, such that a single interface device (e.g.,
a cable or a wireless transmitter/receiver) can be selectively
mated to either of the connectors.
[0027] One method further comprises forming first external
terminals and second external terminals on one of the insulative
sheets, and forming first and second electrically conductive traces
on the one insulative sheet, such that they are electrically
coupled respectively between the vias and the first and second
external terminals. This method further comprises bonding the one
electrically insulative sheet to another one of the insulative
sheets, and electrically coupling the first connector terminals and
second connector terminals respectively to the first external
terminals and the second external terminals.
[0028] Other and further aspects and features of the invention will
be evident from reading the following detailed description of the
preferred embodiments, which are intended to illustrate, not limit,
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The drawings illustrate the design and utility of preferred
embodiments of the present invention, in which similar elements are
referred to by common reference numerals. In order to better
appreciate how the above-recited and other advantages and objects
of the present inventions are obtained, a more particular
description of the present inventions briefly described above will
be rendered by reference to specific embodiments thereof, which are
illustrated in the accompanying drawings. Understanding that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered limiting of its scope, the invention
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0030] FIG. 1 is a plan view of a vibration analysis and
suppression system constructed in accordance with one preferred
embodiment of the present inventions;
[0031] FIG. 2 is a perspective view of one embodiment of a
piezoelectric package that can be used as a vibration sensing
device or vibration actuating device within the system of FIG.
1;
[0032] FIG. 3 is a perspective view of one of the piezoelectric
cells of the piezoelectric package of FIG. 2;
[0033] FIG. 4 a cross-sectional view of the piezoelectric cell,
taken along the line 4-4;
[0034] FIG. 5 is a partially cut-away perspective view of the
piezoelectric cell of FIG. 3, wherein the insulative structure is
transparent to show the internal components of the piezoelectric
cell;
[0035] FIG. 6 is a perspective view of an external connector used
in the piezoelectric cell of FIG. 3;
[0036] FIG. 7 is a plan view of the conductive pathways used to
electrically couple board terminals to vias within a piezoelectric
cell and between the piezoelectric cells of the piezoelectric
package of FIG. 2;
[0037] FIG. 8 is an exploded view of a laminate structure that can
be cured to form the piezoelectric package of FIG. 2;
[0038] FIG. 9 is a perspective view of the laid-up laminate
structure of FIG. 8; and
[0039] FIG. 10 is a cross-sectional view of the laid-up laminate
structure of FIG. 9, taken along the line 10-10.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0040] Referring to FIG. 1, a vibration analysis and suppression
system 10 constructed in accordance with one embodiment of the
present inventions is described. The system 10 is designed to sense
and suppress vibrations within the host structure 12 of equipment
whose performance is highly sensitive to vibration. To this end,
the system 10 generally comprises a plurality of vibration sensing
devices 14, a plurality of vibration actuating devices 16, and a
controller 18 coupled to the vibration sensing devices 14 and
vibration actuating devices 16 via cables 20. Alternatively, the
controller 18 can be coupled to the vibration sensing devices 14
and vibration actuation devices 16 via other interface devices,
such as wireless transmitter/receivers. The vibration sensing
devices 14 sense environmental vibrations within the host structure
12 and feed vibration response information back to the controller
18, which generates and transmits vibration control signals to the
vibration actuating devices 16, which then respond by inducing
vibrations within the host structure 12 to suppress the
environmental vibrations. The vibration sensing devices 14 and
vibration actuating devices 16 are both shown as being mounted to
the exterior surface of the host structure 12, e.g., using a quick
setting adhesive, such as epoxy, although in alternative
embodiments, these devices can be embedded within the host
structure 12.
[0041] While separate and dedicated vibration sensing devices 14
and vibration actuating devices 16 are shown, the functionality of
these devices can be combined into a single vibration
sensing/actuating device. In the illustrated embodiment, the
controller 18 is remote from the host structure 12, although in
alternative embodiments, the controller 18 can be located on the
host structure 12 or anywhere else on the equipment. In other
embodiments, the circuitry of the controller 18 is collocated with
one of, or distributed amongst, the vibration sensing devices 14
and vibration actuating devices 16, similar to the manner disclosed
in U.S. patent application Ser. No. 11/262,083, which is expressly
incorporated herein by reference. It should be appreciated that the
system 10 can alternatively be used to perform non-destructive
testing of the host structure 12, in which case, vibration
actuating devices 16 may not be utilized.
[0042] Referring to FIG. 2, each of the vibration sensing devices
14 and vibration actuating devices 16 takes the form of a
piezoelectric package 22, the use of which will characterize the
device as either a vibration sensing device 14 and/or a vibration
actuating device 16. That is, the piezoelectric package 22 can be
characterized as a vibration sensing device 14 if vibration sensing
signals are transmitted from the piezoelectric package 22 to the
controller 18, and can be characterized as a vibration actuating
device 16 if vibration control signals are transmitted from the
controller 18 to the piezoelectric package 22. In the illustrated
embodiment, the piezoelectric package 22 takes the form of a stiff,
low-profile card that can be bonded to the exterior surface of, or
embedded within, the host structure 10 without substantially
changing the structural or physical response characteristics of the
host structure 10. For the purposes of this specification, an
element is stiff if it exhibits a Young's modulus greater than
1.times.10.sup.5.
[0043] Significantly, the piezoelectric package 22 is scalable in
that its size can be conveniently decreased without adversely
affecting the function of the piezoelectric package 22. In
particular, the piezoelectric package 22 is topologically divided
into a plurality of piezoelectric cells 24, any of which can be
selectively removed from the remaining portion of the package 22.
In the illustrated embodiment, the piezoelectric package 22
includes nine piezoelectric cells 24. It should be appreciated,
however, that the number of piezoelectric cells 24 in any
particular package 22 can be any plurality number, including two
piezoelectric cells 24. In the illustrated embodiment, weakened
borders 25 are provided between the piezoelectric cell 24 to
facilitate separation of the piezoelectric cells 24 from each
other. Such weakened borders 25 can be formed, e.g., via
perforations made between the piezoelectric cells 24, such that the
selected piezoelectric cells 24 can simply be broken off from the
remainder of the piezoelectric package 22. Alternatively, the
piezoelectric cells 24 can be separated from each other by cutting
(e.g., using a saw) selected piezoelectric cells 24 from the
remainder of the piezoelectric package 22.
[0044] Referring further to FIGS. 3 and 4, one embodiment of the
piezoelectric cell 24 (which is representative of each of the cells
24 illustrated in FIG. 2) will now be described. The piezoelectric
cell 24 comprises a pair of piezoelectric plates 26, and in
particular, an upper piezoelectric plate 26' and a lower
piezoelectric plate 26''. It should be appreciated, that the terms
"upper" and "lower" are relative and will depend on the orientation
of the piezoelectric cell 24. For the purposes of this
specification, however, the upper piezoelectric plate 26' will be
directly above the lower piezoelectric plate 26'' when the
piezoelectric cell 24 is placed on its planar surface.
[0045] As best shown in FIG. 2, the piezoelectric plates 26 (only
the upper piezoelectric plate 26' shown in phantom), span the area
of the piezoelectric cell 24, with the exception of a border
extending around the piezoelectric cell 24. Furthermore, the planar
surfaces of the piezoelectric plates 26 have the same area and
generally overlie each other. In the illustrated embodiment, only a
single pair of piezoelectric plates 26 is provided, although the
piezoelectric cell 24 may include more pairs of piezoelectric
plates 26 arranged either in one-dimensional or two-dimensional
array.
[0046] As best shown in FIG. 4, each piezoelectric plate 26 has a
core 28 and a pair of opposing electrodes 30 disposed on the
opposing surfaces of the core 28. That is, a top electrode 30' is
disposed on the top surface of the core 28 and a bottom electrode
30'' is disposed on the bottom surface of the core 28. It should be
appreciated that the terms "upper", "lower", "top", and "bottom"
are relative and will depend on the orientation of the
piezoelectric cell 24. For the purposes of this specification, when
the either of the planar surfaces of the piezoelectric cell 24 is
resting on a surface, the "upper" is above "lower," and "top," is
above "bottom." Each of the electrodes 30 is planar in nature, and
can be formed on the opposing surfaces of the core 28 using any
suitable process, e.g., electroplating or sputtering. The core 28
can be composed of any suitable piezoelectric material, such as,
e.g., lead zirconate titanate (PZT), and the electrodes 30 can be
composed of any suitable electrically conductive material, such as
nickel.
[0047] Each piezoelectric plate 26 has a relatively small
thickness; for example, between 5-100 mils thick. In the
illustrated embodiment, the thickness of the piezoelectric plates
24 is 60 mils. Notably, for purposes of sensing, thicker
piezoelectric plates 24 function better. Such a relatively small
thickness allows high electrical field strengths to be achieved
when a small amount of voltage (e.g., 10-50V) is applied or induced
between the electrodes 30 and advantageously reduces the profile of
the piezoelectric cell 24, and thus, the piezoelectric package
22.
[0048] The piezoelectric cell 24 further comprises a rigid
electrically insulative structure 32 that encapsulates the
piezoelectric plates 26. In addition to insulating and protecting
the piezoelectric plates 26 (which due to their small thicknesses,
are fragile and may break due to irregular stresses when handled,
assembled, or cured), the electrically insulative structure 32
provides a rigid structure to which various elements (described
below) can be integrated into the piezoelectric cell 24. The
electrically insulative structure 32 can be composed of any
suitable material, such as a composite material, as will be
described in further detail below. In the illustrated embodiment,
the insulative structure 32 forms the piezoelectric cell 24, and
thus, the piezoelectric package 22, into the shape of a board,
which when all of the components are incorporated, takes the form
of a printed circuit board, as will be described in further detail
below.
[0049] As best shown in FIG. 2, the piezoelectric cell 24 further
comprises a pair of external connectors 34, and in this case, a
unimorph connector 34' and a bimorph connector 34'', suitably
mounted to the outside of the insulative structure 32. As best
shown in FIG. 6, each of the external connectors 34 has a plurality
of connector terminals 36, and in this case, four connector
terminals 36 (labeled 1-4), which are electrically coupled
respectively to the four electrodes 30 of the piezoelectric plates
26, as will be described in further detail below. The connector
terminals 36 are also capable of mating with a connector (not
shown) at the end of the cable 20 (shown in FIG. 1).
[0050] Significantly, with the exception of the connector of the
cable 20 that mates with the piezoelectric package 22, the cable is
standard (containing two conductors for the signal and ground) and
interfaces with the controller 18 in a standard manner (i.e., the
connector of the cable 20 that mates with the controller 18
includes two terminals (pins or sockets) that interfaces with two
standard terminals (not shown) on the controller 18. Thus, when the
cable 20 is mated to either of the connectors 34, the signal
conductor within the cable 20 will be connected to two connector
terminals 36, and the ground conductor within the cable 20 will be
connected to the other two connector terminals 36. In one
embodiment, the cable 20 takes the form of a coaxial cable, and the
connector that mates with the controller 18 takes the form of a
bayonet Neill-Concelman (BNC) connector. As briefly discussed
above, instead of a cable 20, a wireless transmitter/receiver (not
shown) can be mated to either of the connectors 34.
[0051] In the illustrated embodiment, each of the connector
terminals 36 takes the form a pin, one end of which is capable of
being inserted into a corresponding socket (not shown) in the
connector of the cable 20, and the other end of which is capable of
being suitably mounted to the terminals on the board, as will be
described in further detail below. It should be appreciated that
the connector terminals 36 can take the form of any suitable
terminals that is capable of mating with a corresponding terminal
of the cable 20. For example, each of the connector terminals 36
can, instead, take the form of a socket (not shown) capable of
mating with a corresponding pin (not shown) in the connector end of
the cable 20. Furthermore, although the connector terminals 36 are
illustrated as being surface mount pins, other types of pins, such
as through-hole pins can be used.
[0052] Significantly, the connector terminals 36 of the external
connectors 34 have identical geometric patterns, so that the cable
20 is capable of being selectively mated with either of the
connectors 34. However, the connector terminals 36 of the external
connectors 34 are electrically coupled to the respective electrodes
30 of the piezoelectric plates 26 in different orders.
[0053] For example, with respect to the unimorph connector 36',
terminal 1 is coupled to the bottom electrode 30'' of the lower
piezoelectric plate 26''; terminal 2 is coupled to the top
electrode 30' of the lower piezoelectric plate 26''; terminal 3 is
coupled to the bottom electrode 30'' of the upper piezoelectric
plate 26'; and terminal 4 is coupled to the top electrode 30' of
the upper piezoelectric plate 26'. With respect to the bimorph
connector 36'', terminal 1 is coupled to the bottom electrode 30''
of the lower piezoelectric plate 26''; terminal 2 is coupled to the
top electrode 30' of the lower piezoelectric plate 26''; terminal 3
is coupled to the top electrode 30' of the upper piezoelectric
plate 26'; and terminal 4 is coupled to the bottom electrode 30''
of the upper piezoelectric plate 26'.
[0054] In this manner, without modifying the controller 12 (shown
in FIG. 1) or its interface with the cable 20, the piezoelectric
cell 24, and thus, the piezoelectric package 22, can be configured
as a unimorph when the cable 20 is mated to the unimorph connector
34', and configured as a bimorph when the cable 20 is mated to the
bimorph connector 34''.
[0055] Referring further to FIG. 5, one exemplary manner in which
the connector terminals 36 of the respective connectors 34 can be
electrically coupled to the electrodes 30 of the piezoelectric
plates 26 in two different orders will now be described. The
piezoelectric cell 24 further comprises a number of internal
electrical conductors 38 (in this case, four conductors 38
corresponding to the four electrodes 30 on the piezoelectric plates
26 and the four terminals 36 on each of the connectors 36)
encapsulated within the insulative structure 32. The conductors 38
may be composed of any suitable electrically conductive material,
such as copper, which as will be described in further detail below,
are consistent with forming the conductors 38 via an electroplating
or chemical etching process.
[0056] In the illustrated embodiment, each conductor 38 includes a
low-profile electrically conductive trace 40 and an electrically
conductive via 42. Each trace 40 is coupled to a corresponding
electrode 30 on one of the piezoelectric plates 26 and extends away
from the electrode 30 in a horizontal direction (i.e., parallel to
the plane in which the piezoelectric plate 26 extends). Each via 42
is extends in a vertical direction (i.e., perpendicular to the
plane in which the piezoelectric plates 26 extends) to the top of
the insulative structure 32. In the illustrated embodiment, each
via 42 is a blind via; i.e., each via 42 is visible only on the top
surface of the board. Significantly, the use of the traces 40 and
vias 42 facilitates electrical coupling to the electrodes 30 of the
piezoelectric plates 26 in any order.
[0057] In particular, as best shown in FIG. 7, the piezoelectric
cell 24 further comprises external board terminals 44, and in
particular, a first set of external board terminals 44' to which
the connector terminals 36 of the unimorph connector 34' can be
electrically coupled, and a second set of external board terminals
44'' to which the connector terminals 36 of the bimorph connector
34'' can be electrically coupled. Notably, for purposes of
illustration, the board terminals 44 are shown as being bare (i.e.,
without the connectors) in FIG. 7. In the illustrated embodiment,
the board terminals 44 take the form of solder pads to which the
respective connector terminals 36 can be soldered, although in
alternative embodiments, the board terminals 44 can be take the
form of any terminals to which the connector terminals 36 can be
connected. For example, the board terminals 44 can take the form of
through-hole terminals (not shown) in the alternative case where
the connector terminals 36 take the form of through-hole pins.
[0058] Although the soldering of the connector terminals 36 to the
respective board terminals 44 affixes the external connectors 34 to
a certain extent, the piezoelectric cell 24 further comprises
mounting pads 46, and in particular, a first pair of mounting pads
46' to which lateral flanges 48 of the unimorph connector 34' can
be affixed, and a second pair of mounting pads 46'' to which
lateral flanges of the bimorph connector 34'' can be affixed
(flanges 48 of generic connector 34 shown in FIG. 6). The
affixation of the connectors 34 to the respective mounting pads 46
can be accomplished using suitable means, e.g., soldering. The
piezoelectric cell 24 can be provided with alignment holes 50, and
in particular, a pair of alignment holes 50' in which corresponding
alignment pins 52 on the bottom of the unimorph connector 34' can
be inserted, and a pair of alignment holes 50'' in which
corresponding alignment pins 52 on the bottom of the bimorph
connector 34'' can be inserted (pins 52 of generic connector 34
shown in FIG. 6), thereby facilitating alignment of the connector
terminals 36 with the board terminals 44 during the mounting
process. Significantly, the first and second sets of board
terminals 44 have identical geometric patterns, so that identical
connectors 36 can be coupled to the board.
[0059] Each set of board terminals 44 is electrically coupled to
the vias 42 (and thus, the electrodes 30 of the piezoelectric
plates 26) via conductors 54 (in this case, electrically conductive
traces shown in dark solid lines). In the illustrated embodiment,
the conductors 54 are disposed on the top surface of the board, but
in alternative embodiments, any of the conductors 54 can be
internally routed within the board to the corresponding vias 42. In
some cases, a terminal on one set can be electrically coupled to a
corresponding via 42 through a terminal on the other set.
Significantly, the first set of board terminals 44' (and thus, the
connector terminals 36 of the unimorph connector 34') are
electrically coupled to the vias 42 (and thus, the electrodes 30 of
the piezoelectric plates 26) in a different order than the second
set of board terminals 44'' (and thus, the connector terminals 36
of the bimorph connector 34'') are electrically coupled to the vias
42 (and thus, the electrodes 30 of the piezoelectric plates
26).
[0060] To facilitate an understanding of these different connector
orders, the vias 42 have been labeled 1-4 from right to left, the
first set of board terminals 44' have been labeled 1-4 from right
to left, and the second set of board terminals 44'' have been
labeled 1-4 from right to left.
[0061] With respect to the first set of board terminals 44' (and
thus, the unimorph connector 34'), board terminal 1 (and thus,
connector terminal 1) is coupled to via 1 (and thus, the bottom
electrode 30'' of the lower piezoelectric plate 26''); board
terminal 2 (and thus, connector terminal 2) is coupled to via 2
(and thus, the top electrode 30' of the lower piezoelectric plate
26''); board terminal 3 (and thus, connector terminal 3) is coupled
to via 3 (and thus, the bottom electrode 30'' of the upper
piezoelectric plate 26'); and board terminal 4 (and thus, connector
terminal 4) is coupled to via 4 (and thus, the top electrode 30' of
the upper piezoelectric plate 26'). Thus, the terminal pattern for
a unimorph configuration is 1-2-3-4.
[0062] In contrast, with respect to the second set of board
terminals 44'' (and thus, the bimorph connector 34''), terminals 3
and 4 have been switched. In particular, board terminal 1 (and
thus, connector terminal 1) is coupled to via 1 (and thus, the
bottom electrode 30'' of the lower piezoelectric plate 26''); board
terminal 2 (and thus, connector terminal 2) is coupled to via 2
(and thus, the top electrode 30' of the lower piezoelectric plate
26''); board terminal 3 (and thus, connector terminal 3) is coupled
to via 4 (and thus, the top electrode 30' of the upper
piezoelectric plate 26'); and board terminal 4 (and thus, connector
terminal 4) is coupled to via 3 (and thus, the bottom electrode
30'' of the upper piezoelectric plate 26'). Thus, the terminal
pattern for a bimorph configuration is 1-2-4-3.
[0063] It should be appreciated that any terminal pattern that
allows the piezoelectric cell 24 to be configured between a
unimorph and a bimorph can be used, and will ultimately depend on
the specific electrodes 30 that the vias 42 are electrically
coupled to and which connector terminals 36 will carry a signal and
which connector terminals 36 will be grounded. In the illustrated
embodiment, connector pins 2 and 4 carry the signal (and are, thus,
both coupled to the signal conductor in the cable 20) and connector
terminals 1 and 3 are grounded (and are, thus, both coupled to the
ground conductor in the cable 20) for both the unimorph and bimorph
configurations.
[0064] As briefly discussed above, the piezoelectric package 22 is
scalable in that selected ones of the piezoelectric cells 24 can be
removed to reduce the size of the package 22. Significantly, the
upper piezoelectric elements 26' in every piezoelectric cell 24 are
electrically coupled together in parallel, and the lower
piezoelectric elements 26'' in every piezoelectric cell 24 are
electrically coupled together in parallel. Thus, each of the
external connectors 34 is electrically coupled to the piezoelectric
elements 26 in every piezoelectric cell 24, so that the cable 20
need only be connected to one connector to operate all of the
piezoelectric cells 24.
[0065] To this end, the piezoelectric package 22 comprises a
plurality of intercellular conductors 56 (and in this case,
electrically conductive traces) that electrically couple
immediately adjacent piezoelectric cells 24 together. For purposes
of clarity, the conductors 56 that couple piezoelectric cells 24 on
the left and on the right are shown in dotted lines, and the
conductors 56 that couple piezoelectric cells 24 at the top and at
the bottom are shown in dashed lines. In the illustrated
embodiment, the intercellular conductors 56 are electrically
coupled between the corresponding vias 42 of the adjacent
piezoelectric cells 24 in a daisy-chain fashion.
[0066] That is, for any two piezoelectric cells 24 that are coupled
together, via 1 is connected to via 1, via 2 is connected to via 2,
via 3 is connected to via 3, and via 4 is connected to via 4. Thus,
each connector 34 will be electrically coupled to other
piezoelectric cells 24 in the same manner that it is electrically
coupled to its own piezoelectric cell 24. Notably, when any of the
piezoelectric cells 24 are removed from the piezoelectric package
22, the functioning of the remaining piezoelectric cells 24 will
not be affected. In particular, the external connectors 34 will
remain electrically coupled to the electrodes 30 of the
piezoelectric plates 26 in their own piezoelectric cell 24, as well
as to the electrodes 30 of the piezoelectric plates 26 in the
remaining piezoelectric cells 24, when any of the intercellular
conductors 56 is severed.
[0067] Having described its structure, a method of manufacturing
the piezoelectric package 22 will be described with respect to
FIGS. 8-10. In this method, the piezoelectric package 22 is created
from a multilayer laminate comprising a layup of two layers of
piezoelectric plates 26 (an upper layer of piezoelectric plates 26'
and a lower layer of piezoelectric plates 26'', two outer
electrically insulative sheets 60 (an upper insulative sheet 60'
and a lower insulative sheet 60''), an inner electrically
insulative sheet 62, and thickening sheets 64 (an upper set of
thickening sheets 64' and a lower set of thickening sheets 64'').
Each of the foregoing sheets can be originally provided in a roll
that is then cut to size. As will be described in further detail
below, this layup is then cured to form a composite structure of
the piezoelectric package 22.
[0068] Each of the insulative sheets 60, 62 and the thickening
sheets 64 is composed of an electrically insulative fiber matrix
impregnated with a resin, and in the illustrated method, a
fiberglass/epoxy pre-impregnated material (e.g., E-761 Epoxy
Pre-Preg with 7781 E-Glass), which has proven to be a good
electrically insulating material with high strength. Alternatively,
other pre-impregnated material compatible to composite
manufacturing techniques can be used. Preferably, such alternative
pre-impregnated material has a Young's modulus similar or greater
than fiberglass/epoxy pre-impregnated material; for example,
Kevlar.RTM./epoxy pre-impregnated material.
[0069] Each of the insulative sheets 60, 62 can have any suitable
thickness; for example, in the range of 5-20 mils when cured. In
the illustrated embodiment, the insulative sheets 60, 62 each have
a 9 mil thickness when cured. The upper set of thickening sheets
64', which will be located on the same plane as the upper
piezoelectric plates 26', preferably have a combined thickness that
is the same as the thickness of the upper piezoelectric plates 26',
and the lower set of thickening sheets 64'', which will be located
on the same plane as the lower piezoelectric plates 26'',
preferably have a combined thickness that is the same as the
thickness of the lower piezoelectric plates 26''.
[0070] Each of the thickening sheets 64 includes a plurality of
windows 66 for respectively receiving the piezoelectric plates 26
therein. In this case, nine windows 66 are provided in each
thickening sheet 64', which corresponds to the nine upper
piezoelectric plates 26', and nine windows 66 fare provided in each
thickening sheet 64'', which corresponds to the nine lower
piezoelectric plates 26''. Of course, any number of windows 66 can
be provided in the thickening sheets 64 depending on the number of
piezoelectric plates 26 that are to be accommodated. Because the
upper layer of piezoelectric plates 26' and lower layer of
piezoelectric plates 26'' will exactly correspond with each other,
the pattern of windows 66 in the upper thickening sheets 64' and
lower thickening sheets 64'' will be identical.
[0071] The method of manufacturing the piezoelectric package 22 is
first initiated by forming the electrically conductive traces 40
onto the insulative sheets 60', 60'', and 62. In particular, a
first set of electrical traces 40 (shown in phantom) is formed on
the lower surface of the upper insulative sheet 60', a second set
of electrical traces 40 is formed on the upper surface of the inner
insulative sheet 62, a third set of electrical traces 40 (not
shown) are formed on the lower surface of the inner insulative
sheet 62, and a fourth set of electrical traces 40 is formed on the
upper surface of the lower insulative sheet 60''. As there shown,
each electrical trace 40 includes a large surface region 41 that
will coincide with one of the electrodes of a corresponding
piezoelectric plate 26, and a relatively small thin region 43 that
will be connected to the corresponding via. The board terminals 44,
mounting pads 46, and electrically conductive traces 54 can be
disposed onto the top surface of the upper insulative sheet 60' in
the desired patterns. The intercellular traces 56 can also be
disposed on selected ones of the thickening sheets 64 in the
desired patterns. The traces 40, board terminals 44, mounting pads
46, traces 54, and traces 56 can be disposed on the respective
insulative sheets using any suitable method, such as chemical
etching or electroplating. The vias 42 can be formed through the
upper insulative sheet 60', insulative sheet 62, and thickening
sheets 64 using suitable means, such as electroplating or insertion
of small rivets.
[0072] Next, the insulative sheets 60, 62, thickening sheets 64,
and piezoelectric plates 26 are laid onto of each other from bottom
to top to form a laminate structure 70 (as shown in FIGS. 9 and
10). When the laminate structure 70 is laid up, the inner
insulative sheet 62 is disposed between the respective upper and
lower layers of piezoelectric plates 26 to electrically isolate
them from each other, while allowing the upper and lower
piezoelectric plates 26 to be located closely adjacent to each
other, and the windows 66 in the thickening sheets 64 are aligned,
so that the piezoelectric plates 26 can be inserted into the
respective windows 66.
[0073] This can be accomplished by aligning the windows 66 of the
lower thickening sheets 64'' over the lower insulative sheet 60'',
inserting the lower piezoelectric plates 26'' within the respective
aligned windows 66, disposing the inner insulative sheet 62 over
the lower thickening sheets 64'' and piezoelectric plates 26'',
aligning the windows 66 of the upper thickening sheets 64 over the
inner insulative sheet 62, inserting the upper piezoelectric plates
26' within the respective aligned windows 66, and disposing the
upper insulative sheet 60'' over the upper thickening sheets 64'
and piezoelectric plates 26'.
[0074] When the piezoelectric plates 26 are inserted within the
corresponding windows 66 of the thickening sheets 64, the large
regions 41 of the electrical traces 40 disposed on the lower
surface of the upper insulative sheet 60' will be in direct
electrical contact with the top electrodes 30' of the respective
upper piezoelectric plates 26', the large regions 41 of the
electrical traces 40 disposed on the upper surface of the inner
insulative sheet 62 will be in direct electrical contact with the
lower electrodes 30'' of the respective upper piezoelectric plates
26', the large regions 41 of the electrical traces 40 disposed on
the lower surface of the inner insulative sheet 62 will be in
direct electrical contact with the top electrodes 30' of the
respective lower piezoelectric plates 26'', and the large regions
41 of the electrical traces 40 disposed on the upper surface of the
lower insulative sheet 60'' will be in direct electrical contact
with the bottom electrodes 30'' of the respective lower
piezoelectric plates 26''.
[0075] After the laminate structure 70 has been laid up, it can be
inserted into an oven and cured. During the curing process, the
resin from the insulative sheets 60, 62, and 64 flows to coat the
fibers within these sheets and fill in any gaps within the
structure that would otherwise form air pockets within the
piezoelectric package 22. The resin then polymerizes into a rigid
composite structure. As a result of this process, the insulative
sheets 60, 62, and 64 form the insulative structure 32 (shown in
FIGS. 3-5).
[0076] Preferably, a vacuum seal is provided around the laminate
structure (e.g., by using a vacuum bag) during the curing process
to enable extraction of unused resin and to produce a thin, low
profile piezoelectric package 22. That is, the vacuum seal makes
use of external atmospheric pressure to compress the laminate
structure and to extract any unwanted air and excess resin. The
laminate structure is preferably cured at the temperature and for a
duration that is recommended by the manufacturer of the insulative
sheets 60, 62, 64. However, care must be taken not to cure the
laminate structure at a temperature that is greater than the Curie
temperature of the piezoelectric plates 26 above which the
piezoelectric properties are lost of the piezoelectric plates 26
(i.e., the dipoles in the piezoelectric plates 26 become randomly
oriented, such that the net motion in response to an electrical
field becomes zero). To this end, the insulative sheets 60, 62, 64
are selected, such that their recommended curing temperature does
not exceed the Curie temperature of the piezoelectric plates 26;
for example, at a temperature of 350.degree. F. Notably, the
temperature at which the resin polymerizes will depend on the exact
composition of the resin. In some embodiments, the resin may
polymerize at relatively low temperatures; for example, at room
temperature, in which case, the laminate structure need only be
heated to room temperature. If the piezoelectric properties of the
piezoelectric plates 26 happen to be lost due to excessive
temperature, the piezoelectric plates 26 can be repolarized.
[0077] After laminate structure of the piezoelectric package 22 has
been fabricated and cured, the external connectors 34 can be
mounted to the board terminals 44 using a suitable means, such as
welding or soldering. The weakened borders 25 (shown in FIG. 2) may
be formed into the piezoelectric package 22, e.g., by perforating
the insulative structure 32 between the piezoelectric cells 24.
After the piezoelectric package 22 has been completely fabricated,
it can optionally be located within an environmental case (not
shown), such as the case described in U.S. patent application Ser.
No. 12/038,782, entitled "Piezoelectric Package With Enlarged
Conductive Layers," which is expressly incorporated herein by
reference.
[0078] At various times between the lay-up of the laminate
structure 70 and the mounting of the external connectors 34 to the
board, the assembly can be electrically tested to ensure that the
board terminals 44 are electrically independent from each other
(via conductance measurements) and that the piezoelectric plates 26
are properly working and oriented (via capacitance measurements).
If conductivity exists between the board terminals 44, sheets of
the laminate structure 70, if not already cured, must be realigned.
Small wires (not shown) can be temporarily soldered to the board
terminals 44 to facilitate the conductivity and capacitance tests.
Notably, as a piezoelectric plate become more restricted, its
capacitance should decrease. For example, the capacitance of a
piezoelectric plate by itself should be the highest, with the
capacitance gradually dropping as the piezoelectric plate is placed
in the lay-up, then in the cured composite, and finally within an
environmental case.
[0079] Although particular embodiments of the present invention
have been shown and described, it should be understood that the
above discussion is not intended to limit the present invention to
these embodiments. It will be obvious to those skilled in the art
that various changes and modifications may be made without
departing from the spirit and scope of the present invention. Thus,
the present invention is intended to cover alternatives,
modifications, and equivalents that may fall within the spirit and
scope of the present invention as defined by the claims.
* * * * *