U.S. patent number 3,885,239 [Application Number 04/050,805] was granted by the patent office on 1975-05-20 for passive modulating component.
This patent grant is currently assigned to The Singer Company. Invention is credited to John F. Zaleski.
United States Patent |
3,885,239 |
Zaleski |
May 20, 1975 |
Passive modulating component
Abstract
1. A passive modulating component comprising, a hollow
conductive body, the interior surface of said body defining a
cavity in the shape of a figure of revolution, a flexible
conductive diaphragm mounted to constitute a portion of said body
and positioned on the axis of said figure, a conductive septum
perpendicular to said axis fastened to said body and having an
axial aperture, and a conductive member positioned on said axis
extending through but insulated from said body at a point opposite
said diaphragm, and passing through said aperture in said
septum.
Inventors: |
Zaleski; John F.
(Pleasantville, NY) |
Assignee: |
The Singer Company (Little
Falls, NJ)
|
Family
ID: |
21967542 |
Appl.
No.: |
04/050,805 |
Filed: |
August 19, 1960 |
Current U.S.
Class: |
342/6; 333/232;
332/145 |
Current CPC
Class: |
H03C
7/02 (20130101) |
Current International
Class: |
H03C
7/02 (20060101); H03C 7/00 (20060101); G01s
009/02 () |
Field of
Search: |
;343/6.5,6.8,100.10,18.4,7.6 ;332/29M,54,56,30 ;250/6A ;325/18,175
;333/82B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Berger; Richard E.
Attorney, Agent or Firm: Kennedy; T. W.
Claims
What is claimed is:
1. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a cavity in the
shape of a figure of revolution, a flexible conductive diaphragm
mounted to constitute a portion of said body and positioned on the
axis of said figure, a conductive septum perpendicular to said axis
fastened to said body and having an axial aperture, and a
conductive member positioned on said axis extending through but
insulated from said body at a point opposite said diaphragm, and
passing through said aperture in said septum.
2. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a cavity having
the shape of a plane figure revolved about an axis, a transverse
conductive septum mounted on said body within said cavity dividing
said cavity into two chambers, said septum having an axial
aperture, said body being formed with first and second apertures at
points where said axis intersects said body, a flexible conductive
diaphragm mounted to cover said first aperture in said body, and a
conductive rod insulated from said body extending through said
second aperture in said body and through said aperture in said
septum, an end of said rod being in proximity to but spaced from
said diaphragm.
3. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a cavity having
the shape of a plane figure revolved about an axis, a transverse
conductive septum mounted on said body within said cavity dividing
said cavity into two chambers, said septum having an axial
aperture, said body being formed with first and second apertures at
points where said axis intersects said body, a flexible conductive
diaphragm mounted to cover said first aperture in said body, and a
conductive rod insulated from said body extending along said axis
through said second aperture in said body and through said aperture
in said septum, said rod being mounted to be axially adjustable in
position.
4. A passive modulating component comprising, a conductive body
having a generally cylindrical interior cavity, said body being
formed with first and second apertures at points where the axis of
said cylinder intersects said body, a flexible conductive diaphragm
mounted on said body and covering said first aperture, and a
conductive rod insulated from said body extending through said
second aperture, one end of said rod being spaced from said
diaphragm by a distance less than the transverse dimension of said
rod, the other end of said rod projecting outside said cavity
beyond said body a distance approximately equal to one half the
free space wavelength of electromagnetic wave energy at the
resonant frequency of said cavity.
5. A passive modulating component comprising, a conductive wall
shaped to define a generally cylindrical cavity, a transverse
conductive septum fastened to said wall within said cavity dividing
said cavity into two chambers, said septum having an axial
aperture, said wall consisting in part of a flexible conductive
diaphragm located on the axis of said cylindrical cavity, and a
conductive rod on said axis extending through but insulated from
said wall, said rod extending through said aperture in said
septum.
6. A passive modulating component comprising, a conductive body
having a generally cylindrical interior cavity, said body being
formed with first and second apertures in those portions
constituting the bases of said cylindrical cavity, a flexible
conductive diaphragm mounted on said body and covering said first
aperture, a transverse conductive plate dividing said cavity into
two chambers, said plate having an aperture coaxial with said first
and second apertures, and a conductive rod insulated from said body
extending through said second aperture in said body and through
said aperture in said plate, said rod being mounted to be axially
adjustable in position.
7. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum being formed with a central aperture, said body being
formed with first and second apertures on the cylindrical axis of
said cavity and aligned with said central aperture in said septum,
and a conductive rod extending from the exterior of said cavity
through said second aperture in said body and through said aperture
in said septum to a point in proximity to said diaphragm, whereby
the end of said rod, said diaphragm and the space therebetween
constitute a capacitor, said rod being insulated from said
body.
8. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum having a central aperture, said body being formed with
first and second apertures one through each base portion of said
cylindrical cavity, both aligned with said central aperture, a
conductive diaphragm fastened to said body and covering said first
aperture, a conductive rod extending through said second aperture
in said body and through said aperture in said septum to a position
with its end in proximity to said diaphragm, and insulating means
in said second aperture for holding said rod radially while
permitting axial adjustment thereof.
9. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum having a central aperture, said body being formed with
first and second apertures one through each base portion of said
cylindrical cavity, both aligned with said central aperture in said
septum, a conductive diaphragm fastened to said body and covering
said first aperture, a conductive rod extending from the exterior
of said cavity through said second aperture and through said
central aperture to a point in proximity to said diaphragm, and a
dielectric bushing in said second aperture for preventing radial
movement of said rod while permitting axial adjustment throughout a
range which includes contact of the end of said rod with said
diaphragm.
10. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum having a central aperture, said body being formed with
first and second apertures one through each base portion of said
cylindrical cavity, both aligned with said central aperture in said
septum, a corrugated conductive diaphragm fastened to said body and
covering said first aperture, said diaphragm being formed with an
aperture small compared to the width of said diaphragm, a
dielectric bushing mounted in said second aperture, and a
conductive rod supported by said bushing and extending from the
exterior of said cavity through said bushing and through said
aperture in said septum to a position with its tip in proximity to
said diaphragm.
11. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum having a central aperture, said body being formed with
first and second apertures one through each base portion of said
cylindrical cavity, both aligned with said central aperture in said
septum, a flexible conductive diaphragm fastened to said body and
covering said first aperture, and a conductive rod insulated from
said body extending through said second aperture in said body, and
through said aperture in said septum, the end of said rod within
said cavity being formed with a tip of reduced diameter, said rod
being axially positioned with said tip in proximity to said
diaphragm.
12. A passive modulating component comprising, a hollow conductive
body, the interior surface of said body defining a generally
cylindrical cavity, a transverse conductive septum fastened to said
body within said cavity dividing said cavity into two chambers,
said septum having a central aperture, said body being formed with
first and second apertures one through each base portion of said
cylindrical cavity, both aligned with said central aperture in said
septum, a flexible conductive diaphragm fastened to said body and
covering said first aperture, a conductive rod insulated from said
body extending from the exterior of said cavity through said second
aperture in said body and through said aperture in said septum,
said rod being of smaller diameter than said aperture in said
septum, and adjustable tuning means in that one of said chambers
which is bounded in part by said diaphragm for varying the resonant
frequency of said cavity.
Description
This invention relates generally to apparatus for modulating
electromagnetic wave energy with intelligence and particularly to a
passive component capable of modulating incident radio frequency
energy with incident acoustic energy.
The usual method of modulating radio frequency energy with acoustic
signals requires the conversion of the acoustic signals to
corresponding electric signals which in turn are employed to
modulate a radio frequency carrier. Recently considerable attention
has been directed to passive components capable of modulating a
radio frequency carrier directly by acoustic signals thereby
eliminating the apparatus required for the acoustic-electric
conversion and its attendant power supplies. The small size, light
weight, and absence of trailing wires makes such a component
attractive for many applications such as use by a reporter moving
through a crowd or use for monitoring sounds occurring in an
explosive atmosphere where power supplies would be hazardous.
Passive components for modulating radio frequency energy with
acoustic energy have been known in the past and in general comprise
a resonant circuit such as a cavity resonator one parameter of
which is varied by mechanical motion induced by incident acoustic
energy. When such a circuit is excited by radio frequency energy of
the proper frequency, the energy in the circuit is modulated by the
acoustic energy and a portion is reflected along the path by which
it entered. One example of such a passive component is described
and claimed in the copending application of John F. Zaleski, Ser.
No. 605,663 filed Aug. 22, 1956 for Passive Microwave
Receiver-Transmitter, now U.S. Pat. No. 3,836,962.
While the passive elements which have been known in the past, such
as the one described in the aforementioned application Ser. No.
605,663, have operated remarkably well, they have been subject to
certain limitations, especially when excited by radio frequency
energy transmitted through space. For example, nearly all practical
applications have required the resonant circuit to be coupled to an
antenna, and the antenna and its coupling arrangement have been
bulkier than desirable. Also, the efficiency has been low,
resulting in a low level of the returned signal.
It is a general object of the present invention to provide improved
apparatus for modulating radio frequency energy directly by
acoustic energy.
Another object is to provide a passive component for modulating
radio frequency energy by acoustic energy which is compact and
readily coupled to other radio frequency components.
Another object is to provide a passive modulating component
complete with antenna which is very compact.
Yet another object is to provide a passive modulating component
exhibiting improved operating characteristics.
Briefly stated, the invention comprises a hollow, generally
cylindrical conductive body the interior of which is divided into
two chambers by means of a septum having an axial aperture. One end
wall of the cylindrical body is comprised in part of a flexible
conductive diaphragm capable of being moved by acoustic energy
impinging thereon. The other end wall includes an axial insulating
bushing through which a conductive rod is threaded. The rod extends
through the aperture in the septum and has one end positioned
adjacent to the diaphragm. The other end protrudes from the body
and constitutes a probe or antenna. Radio frequency energy of the
proper frequency reaching the antenna end of the rod is transmitted
to the interior where a symmetrical field is set up. Acoustic
energy incident on the diaphragm alters the resonant frequency
causing modulation of the radio frequency energy, a portion of
which is reflected and transmitted to the antenna end of the
rod.
For a clearer understanding of the invention references may be made
to the following detailed description and the accompanying drawing,
in which:
FIG. 1 is an end elevation view of the modulating component;
FIG. 2 is an axial cross sectional view taken on the line 2--2 of
FIG. 1;
FIG. 3 is a transverse sectional view taken on the line 3--3 of
FIG. 2;
FIG. 4 is an enlarged elevation view of the diaphragm, partly
schematic;
FIG. 5 is a schematic cross sectional view of the diaphragm, taken
on the line 5--5 of FIG. 4; and
FIG. 6 is a pictorial view of the device with a reflector
added.
The modulating component of the invention is generally cylindrical
in shape and in the elevation view of FIG. 1 there can be seen an
end plate 11, the heads of the eight bolts which hold the assembly
together, and the outline of a cylindrical recess 12 through which
the acoustic energy enters. As best shown in FIG. 2, the end plate
11 comprises the flat circular portion visible in FIG. 1 and an
axial sleeve portion 13 which defines the recess 12. A block 14 has
an axial aperture into which the sleeve portion 13 fits and is
formed with an annular lip 15 which cooperates with the sleeve
portion 13 to hold a thin circular conductive diaphragm 16 in
place. The assembly consisting of the end plate 11, the diaphragm
16 and the block 14 is held together by four bolts, ninety degrees
apart, one of which, the bolt 17, is visible in FIG. 2.
A central annular member 21 has an external annular lip portion 22
on one end which fits over the outside of the block 14 while the
other end has a small portion of the exterior surface cut away. A
plate like septum 23 with an axial aperture is formed integrally
with the member 21 opposite the cut away portion. The diaphragm 16,
the block 14, the member 21 and the septum 23 define a first
chamber designated generally by the reference character 24.
A cup shaped member 26 has threads formed on its exterior surface
except for one end which has an annular projection 27 which fits
into the previously mentioned cut away portion in the member 21.
The base of the member 26 has an axial aperture with internal
threads which cooperate with the external threads of a dielectric
bushing 28. The bushing 28 is preferably made of a low loss
dielectric, transparent to radio frequency energy, such as one of
those sold under the names "Stycast" or "Teflon." The interior
surfaces of the cup shaped member 26, the septum 23, and the
bushing 28 define a second chamber, designated generally by the
reference character 29. The entire assembly including the end plate
11, the block 14, the annular member 21, and the cup shaped member
26 are fastened together by means of four bolts spaced ninety
degrees apart, threaded into the member 26. One of these bolts, the
bolt 31, is visible in FIG. 2.
The bushing 28 has an axial aperture through which is threaded a
conductive rod 33, the right end of which, as viewed in FIG. 2, is
frustro-conical in shape, having a flattened tip. The rod 33
extends through the chamber 29, through the aperture in the septum
23, and through the chamber 24 to a position such that the tip
nearly, but not quite, touches the diaphragm 16. The left end of
the rod 33 extends beyond the main body of the apparatus and
constitutes a probe or antenna for receiving and transmitting radio
frequency energy and additionally is provided with a small axial
aperture 35 into which the inner conductor of a coaxial cable may
be fitted. The cylindrical walls of the chambers 24 and 29
cooperate with the axial conductive rod 33 to constitute two
coaxial cavity resonators, the resonant frequency of which may be
adjusted by means of a tuning screw 34 which extends through the
cylindrical wall of the member 21 into the chamber 24. As best
shown in FIG. 3, the screw 34 is angularly positioned so as not to
interfere with any of the bolts holding the assembly together.
In operation, the rod 33 is first adjusted so that the flattened
tip is very close to the diaphragm 16. Radio frequency energy
incident on the protruding end of the rod is propagated through the
coaxial line comprising the rod 33, bushing 28 and the end of the
cup shaped member 26, to the chambers 29 and 24 where standing
waves in the symmetrical TEM mode are set up. The tuning screw 34
is adjusted to match the resonant frequency of the cavities to that
of the incident radio frequency energy. Acoustic energy entering
the recess 12 causes the diaphragm 16 to move in accordance with
the compressions and rarifactions of the acoustic signal. The
spacing between the diaphragm 16 and the tip of the rod 33 is
likewise varied, thus varying the capacitance between the rod and
the diaphragm. The latter variation causes at least two forms of
modulation. First, amplitude modulation is produced since when the
cavity is resonant at the frequency of the impressed radio
frequency a relatively large amount of power is absorbed while only
a small mount is reflected. As the capacitance between rod and
diaphragm is varied, the resonant frequency varies, causing a
greater amount of power to be reflected. Second, phase modulation
is introduced since as the resonant frequency varies above and
below that of the impressed frequency, the impedance of the cavity
changes from capacitative to inductive thereby producing a change
in the phase of the reflected energy. It has been found that the
reflected signal can be recovered satisfactorily by the use of
either an amplitude modulation detector or a phase modulation
detector, although the latter is preferred in most instances
because of the more favorable signal to noise ratio inherently
obtainable.
A specific embodiment of the invention has been constructed for use
with microwave energy in the X band range of frequencies. In this
embodiment, the internal diameter of the cavities was made 0.500
inch, the internal distance from the block 11 to the septum 23 was
made 0.265 inch. the septum 23 was made 0.035 inch thick where it
joins the block 21 and inch inch thick at the portion nearer the
center of the cavities, the internal diameter of the thicker
portion was made 0.343 inch, the aperture in the septum was made
inch 0.125 inches in diameter, and the distance from the thicker
portion of the septum to the end portion of the block 26 was made
0.220 inch. The rod 33 was 0.125 inch in diameter at the protruding
end, the interior portion being reduced to a diameter of 0.093
inch, and the flat tip was made 0.020 inch in diameter. The rod had
a total length of 1.343 inches so that it protruded beyond the
bushing 28 a distance of about 0.63 inch which is approximately one
half wavelength at 9,000 mcps. All of the parts except the
diaphragm 16 and the dielectric bushing 28 were made of brass. It
was found that a spacing of from 0.001 inch to 0.005 inch between
the tip of the rod 33 and the diaphragm 16 provided excellent
operation under normal circumstances, although a spacing of as
little as 0.0001 inch has been used when extreme sensitivity has
been required.
The diaphragm 16 should have a number of properties. It must be of
conductive material so as to cooperate with the tip of the rod 34
and to complete the electrical enclosure of the chamber 24. The
diaphragm must be compliant enough to move in response to acoustic
energy yet strong enough so as not to be permanently deformed
thereby. It must have sufficient resilience to provide a restoring
force to maintain the diaphragm in a neutral position in the
absence of acoustic signals. It must be thicker than the skin
penetration of the radio frequency energy. One form of diaphragm
which has been found to be satisfactory is illustrated in FIGS. 4
and 5 and comprises an aluminum disc approximately 0.0002 inch
thick and approximately 1/4 inch in diameter. The outer 1/32 inch
is held between the end plate 11 and the block 14, leaving an
active diameter of about 3/16 inch. The active portion is stiffened
by concentric corrugations approximately 0.005 inch deep and
approximately 0.010 inch between crests. As best shown in FIG. 5,
these corrugations extend over the active portion of the diaphragm
except for a small portion about 0.030 inch in diameter at the
center. It has been found that the chambers 24 and 29 constitute
too much of an acoustic load for the diaphragm and that performance
is improved by forming a small hole 37 about 0.005 inch to 0.010
inch in diameter in the diaphragm. Additionally, the hole 37
equalizes the pressures on opposite sides of the diaphragm. As is
obvious from the dimensions given above, FIGS. 4 and 5, especially
FIG. 5, are not drawn to scale and must be regarded as schematic
only.
The resonant frequency of a reentrant cavity, such as the chamber
24, depends on many factors, such as the length, the diameter, the
size of the central conductor, the spacing of the tip of the
central conductor from the end wall, and the arrangement for
coupling energy into and out of the cavity. No simple formula is
known for predicting the resonant frequency for the various
possible configurations and accordingly the design of the present
invention has necessarily been in part a process of trial and
error. It has been found that the chamber 24 with the dimensions
given above is resonant at about 9,000 mcps, the exact frequency
depending upon the adjustment of the tuning screw 34. The chamber
29 is not provided with a separate tuning screw but its resonant
frequency is affected by the impedance reflected from the cavity 24
so that both cavities may be tuned by the single tuning screw 34.
It has been found that both cavities can be tuned to resonance by
the screw 34 over the range from about 8,500 mcps to about 9,500
mcps.
The component of the present invention may be coupled readily to
other microwave components, such as a coaxial line or a waveguide,
by means of the external threads on the member 26. In the case of a
waveguide, the device may be screwed into a suitable bushing in the
wall of the waveguide in which case the protruding end of the rod
33 constitutes a probe for coupling microwave energy in both
directions. In the case of a coaxial line, the inner conductor may
be clamped to the end of the rod 33, aided by the hole in the end,
while the outer conductor may be held by the exterior threads on
the body of the component.
The present invention is also suitable for use in those
applications wherein a microwave transmitter and receiver are
located at a remote point and in which the microwave energy is
transmitted unguided through space to and from the device. When
positioned with the protruding end of the rod vertical, the device
has omnidirectional characteristics for vertically polarized waves.
If directivity is desired, it may be obtained readily by the use of
a reflector such as shown in FIG. 6.
Turning now to FIG. 6, there is shown to a smaller scale, the
component previously described but with a reflector added. The
reflector comprises a hollow semi-cylindrical portion 41 and a full
hollow cylindrical portion 42, both made from a single piece of
brass pipe. The portion 42 is provided with internal threads, not
visible in the drawing, which engage the external threads on the
cup shaped member 26. One satisfactory reflector had an overall
length of about 11/4 inches so that it extended beyond the end of
the rod 33, as shown, although it will be understood that the
dimensions are not critical.
A device in accordance with the present invention was compared
directly with a device constructed in accordance with the teachings
of the aforesaid copending application Ser. No. 605,663.
Differences which might have been caused by differences in the
directivity patterns of the two antennas were eliminated by
exciting both devices directly by a waveguide. With identical
carrier and acoustic signals the device of the present invention
produced a return signal 6db stronger than that produced by the
device of the application Ser. No. 605,663. The improvement is
believed to be due largely to the simpler coupling arrangement of
the present invention which permits a greater portion of the
incident energy to be converted to the symmetrical TEM mode within
the cavities.
* * * * *