U.S. patent number 3,836,962 [Application Number 03/605,663] was granted by the patent office on 1974-09-17 for passive microwave receiver-transmitter.
This patent grant is currently assigned to The Singer Company. Invention is credited to John F. Zaleski.
United States Patent |
3,836,962 |
Zaleski |
September 17, 1974 |
PASSIVE MICROWAVE RECEIVER-TRANSMITTER
Abstract
1. A microwave transducer comprising, a microwave resonant
cavity, a randomly embossed thin metallic diaphragm closing one
face thereof, a conical metallic post extending from one wall of
said cavity towards said diaphragm having a sharp tip in close
proximity to but spaced from said diaphragm, and means for coupling
microwave energy into and out of said microwave resonant
cavity.
Inventors: |
Zaleski; John F. (Valhalla,
NY) |
Assignee: |
The Singer Company (New York,
NY)
|
Family
ID: |
24424660 |
Appl.
No.: |
03/605,663 |
Filed: |
August 22, 1956 |
Current U.S.
Class: |
342/6; 332/163;
333/230; 332/144 |
Current CPC
Class: |
H04B
7/145 (20130101) |
Current International
Class: |
H04B
7/145 (20060101); G01s 009/56 () |
Field of
Search: |
;343/18R,18RM,771
;332/56 ;333/8B |
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 microwave transducer comprising, a microwave resonant cavity,
a randomly embossed thin metallic diaphragm closing one face
thereof, a conical metallic post extending from one wall of said
cavity towards said diaphragm having a sharp tip in close proximity
to but spaced from said diaphragm, and means for coupling microwave
energy into and out of said microwave resonant cavity.
2. A microwave transducer comprising, a microwave resonant cavity,
a randomly embossed thin metallic diaphragm forming a closure for
one wall thereof, a conical metallic post extending from the
opposite wall of said cavity towards said diaphragm having a sharp
tip in close proximity to but spaced from the underside of said
diaphragm, means for acoustically impedance matching said
diaphragm, and means for coupling microwave energy into and out of
said microwave resonant cavity.
3. A microwave transducer comprising, a waveguide section, a
plurality of microwave radiating elements positioned along the
length thereof, a microwave resonant cavity positioned internally
of said waveguide section, microwave coupling means between said
cavity and said waveguide section, said microwave cavity being
provided with a randomly embossed thin metallic diaphragm forming a
closure for one wall thereof, one face of said diaphragm being
exposed to the atmosphere through an aperture formed in the wall of
said waveguide section, and a metallic post positioned interiorly
of said cavity extending from the wall thereof opposite said
diaphragm towards said diaphragm and terminating in a sharp tip
positioned in close proximity to but spaced from the underside of
said diaphragm.
4. A microwave transducer comprising, a waveguide section, a
plurality of microwave radiating elements positioned along the
length thereof, a microwave resonant cavity positioned internally
of said waveguide section having one face thereof exposed to the
atmosphere through an aperture formed in the wall of said waveguide
section, microwave coupling means between said cavity and said
waveguide section, the exposed face of said cavity being
constituted by a randomly embossed thin metallic diaphragm affixed
to said cavity, a metallic post positioned interiorly of said
cavity extending from the center of the wall thereof opposite said
diaphragm towards said diaphragm and terminating in a sharp tip
positioned in close proximity to but spaced from the underside of
said diaphragm, and means for acoustically impedance matching said
diaphragm.
5. A microwave transducer comprising, a rectangular waveguide
section, a plurality of microwave radiating slots positioned along
one broad face thereof, a microwave resonant cavity member
positioned at one end of said waveguide section internally thereof
with one face of said cavity substantially coextensive with said
broad face of said waveguide section and exposed to the atmosphere
through an aperture in said waveguide wall which encompasses said
cavity member, said cavity member being provided with a randomly
embossed thin metallic diaphragn affixed to said cavity member and
forming the exposed face thereof, a conical metallic post extending
centrally of the wall of said cavity opposite said diaphragm in a
direction towards said diaphragm and terminating in a sharp tip
positioned in close proximity to but spaced from the underside of
said diaphragm, and microwave coupling means between said cavity
and said waveguide section.
6. A microwave transducer comprising, a rectangular waveguide
section, a plurality of microwave radiating slots positioned along
one broad face thereof, a microwave resonant cavity member
positioned at one end of said waveguide section extending between
the broad faces thereof with one face of said cavity exposed to the
atmosphere through an aperture formed in a broad face of said
waveguide section of a size such as to encompass said cavity
member, a randomly embossed thin metallic diaphragm affixed to said
cavity member and forming the exposed face thereof, a conical
metallic post positioned internally and centrally of said cavity
member and extending axially of said cavity member in a direction
toward said diaphragm, said conical post terminating in a sharp tip
positioned in close proximity to but spaced from the underside of
said diaphragm, microwave coupling means between said cavity and
said waveguide section, and means for acoustically impedance
matching said diaphragm.
7. A microwave transducer comprising, a rectangular waveguide
section, a plurality of microwave radiating slots positioned
linearly along one broad face thereof, a cylindrical body member
inserted through an aperture in said broad face at one end of said
waveguide section, said body member extending between the broad
faces of said waveguide section and having one end thereof exposed
through said aperture, a cylindrical microwave resonant cavity
formed in said body member concentric therewith, a randomly
embossed thin metallic diaphragm affixed to said one end of said
body member and forming a face of said cavity substantially
contiguous with the broad face of said waveguide section, a conical
metallic post positioned axially of said cavity and extending in a
direction towards said diaphragm, said conical post terminating in
a sharp tip positioned in close proximity to but spaced from the
underside of said diaphragm, and microwave coupling means between
said cavity and said waveguide section.
8. A microwave transducer comprising, a rectangular waveguide
section, a plurality of microwave radiating slots positioned
linearly along one broad face thereof, a cylindrical body member
inserted through an aperture in said broad face at one end of said
waveguide section, said body member extending between the broad
faces of said waveguide section and having one end thereof exposed
through said aperture, a cylindrical microwave resonant cavity
formed in said body member concentric therewith, a randomly
embossed thin metallic diaphragm affixed to said one end of said
body member and forming a face of said cavity substantially
contiguous with the broad face of said waveguide section, a conical
metallic post positioned axially of said cavity and extending in a
direction towards said diaphragm, said conical post terminating in
a sharp tip positioned in close proximity to but spaced from the
underside of said diaphragm, microwave coupling means between said
cavity and said waveguide section, and means for acoustically
impedance matching said diaphragm.
9. A microwave transducer comprising, a body member having a
microwave resonant cavity formed in one end thereof and extending
longitudinally of said body for a portion of the length thereof, a
recess extending longitudinally into said body from the other end
thereof and terminating short of said cavity whereby a partition
extends between said cavity and said recess, a randomly embossed
thin metallic diaphragm affixed to said body member adjacent the
first mentioned end thereof forming a face of said microwave
cavity, a conical metallic post affixed to said partition and
extending axially of said microwave cavity towards said diaphragm,
said post terminating in a sharp tip positioned in close proximity
to but spaced from the underside of said diaphragm, a plurality of
apertures formed in said partition of a size to permit air
communication between said cavity and said recess but below the
cut-off frequency for microwave energy whereby said microwave
cavity and said recess together constitute an acoustical impedance
match for said diaphragm, air vent means in said diaphragm, and
means for coupling microwave energy to said microwave cavity.
10. A microwave transducer as set forth in claim 9 in which said
body member is contained in a rectangular waveguide section between
the broad faces thereof with the diaphragm exposed to the
atmosphere, and said waveguide section is provided with microwave
radiating elements along the length thereof.
11. A microwave transducer comprising, a cylindrical body member
having a cylindrical microwave resonant cavity formed in one end
thereof concentric therewith and extending longitudinally of said
body member for a fraction of the length thereof, a cylindrical
recess formed in the other end of said body member concentric
therewith and extending longitudinally of said body for such
fraction thereof as to provide a partition wall between said cavity
and said recess, a plate member closing the face of said recess
remote from said partition, a randomly embossed thin metallic
diaphragm affixed to said body forming an end closure for said
resonant cavity, a conical metallic post extending from said
partition axially of said cavity towards said diaphragm, said post
terminating in a sharp tip positioned in close proximity to but
spaced from the underside of said diaphragm, a plurality of
communicating apertures in said partition having dimensions less
than the cut-off frequency for which the resonant cavity is
designed whereby said microwave cavity together with said recess
constitute an acoustical impedance matching chamber but microwave
energy is precluded from entering said recess, an air vent in said
diaphragm, and means impervious to air for coupling microwave
energy to said cavity.
12. A microwave transducer as set forth in claim 11 in which said
body member is contained in a rectangular waveguide section between
the broad faces thereof with the diaphragm exposed to the
atmosphere, and said waveguide section is provided with microwave
radiating elements along the length thereof.
13. A microwave transducer comprising, a rectangular waveguide
section, a plurality of radiating slots positioned along one broad
face thereof, said broad face being recessed over the area occupied
by said slots, a dielectric membrane covering said recessed area, a
microwave resonant cavity member positioned at one end of said
waveguide section and extending between the broad sides thereof
with one face thereof exposed to the atmosphere through an aperture
in one of said broad sides encompassing said cavity member, a
randomly embossed thin metallic diaphragm affixed to said cavity
and forming the face thereof exposed to the atmosphere, a metallic
post extending from the wall of said cavity opposite said diaphragm
in a direction towards said diaphragm, said post terminating in a
sharp tip positioned in close proximity to but spaced from said
diaphragm, microwave coupling means between said waveguide section
and said cavity, and a closure plate for the end of said waveguide
section opposite the end to which said cavity is affixed, said
closure plate being perforated for acoustical and air transmission
therethrough.
14. A microwave transducer comprising, a rectangular waveguide
section, a plurality of shunt radiating slots positioned linearly
along one broad face thereof, said broad face being recessed over
the area occupied by said slots, a dielectric membrane affixed to
said waveguide section covering said recessed area, a cylindrical
body member set into said broad face at one end of said waveguide
section with its surface substantially flush therewith and its
axial length extending between the broad faces of said waveguide
section, a resonant microwave cavity formed in said body member
concentric therewith, a randomly embossed thin metallic diaphragm
affixed to said body member and forming a closure for said cavity
at the end thereof adjacent said one broad face, a conical metallic
post positioned axially of said cavity terminating in a sharp tip
positioned in close proximity to but spaced from said diaphragm,
microwave coupling means between said waveguide section and said
cavity, and a closure plate affixed to the end of said waveguide
section opposite the end to which said cavity is affixed, said
closure plate being perforated for acoustical and air transmission
therethrough.
Description
This invention relates to a passive microwave receiver and
transmitter and particularly to a device wherein microwave energy
transmitted from a location remote thereto is received, modulated
by adjacent acoustical energy and the microwave energy so modulated
retransmitted for reception at the transmitting or other
location.
Frequently it is desirable that audible sounds present at some
particular location be transmitted to points remote therefrom by
radio links. At the same time because of lack of power facilities,
presence of explosive atmosphere, or other reasons it is
undesirable or impossible to provide such location with power
supplies, apparatus for generating electro-magnetic waves and the
attendant equipment required to generate and radiate modulated
signals. To this end the present invention contemplates the
provision of a small compact device which requires no power
supplies, contains no equipment liable to produce igniting
electrical discharges and at the same time will receive microwave
energy generated at and transmitted from a remote point, modulate
the energy so received in accordance with locally produced
acoustical signals, and retransmit the modulated energy to the
remote transmitting or other points where the intelligence may be
suitably extracted.
In general the invention comprises a microwave resonant cavity of
small compact design having associated therewith an acoustically
actuated member so arranged and integrated with the resonant cavity
structure as to modulate microwave energy caused to impinge thereon
in a highly efficient manner. At the same time the acoustical
member is so designed and so combined with the microwave elements
associated therewith that the acoustical characteristics are
maintained uniform over a wide band of acoustical frequencies.
Where extreme compactness is desired the acoustically modulated
microwave cavity may itself constitute the mechanism for receiving
microwave energy, modulating it and reradiating the modulated
energy. In other instances where higher levels of energy return are
desired the acoustically modulated microwave cavity may be coupled
to a small microwave antenna which acts as the receiving and
reradiating instrumentality.
It is also contemplated that when a microwave antenna is used in
conjunction with the acoustically modulated microwave cavity, the
antenna may itself be so constructed as to constitute an acoustic
matching impedance for the acoustic elements of the system so that
broad band acoustic properties are maintained.
A purpose of the invention, therefore, is to provide a compact
device requiring no power supply which will transmit required
intelligence to remote locations.
Another purpose of the invention is to provide a passive device for
transmitting intelligence to remote locations which has a broad
acoustical range of substantially uniform flat characteristic.
Another purpose of the invention is to provide a device having good
acoustical properties which will efficiently modulate and transmit
remotely generated electromagnetic energy.
The invention will be more readily understood from the following
detailed description, considered together with the attached drawing
in which:
FIG. 1 is an exterior view of one form of the invention.
FIG. 2 is a sectional view of the microwave cavity and its
associated acoustical elements taken on the line 2--2 of FIG.
1.
FIG. 3 is an exterior view of a modified form of the invention.
FIG. 4 is a sectional view of the microwave cavity taken on the
line 4--4 of FIG. 3.
FIG. 5 is a sectional view taken on the line 5--5 of FIG. 3.
Referring now to FIG. 1, a section of rectangular waveguide 11 is
provided along one broad face thereof with a plurality of shunt
slots 12, 13, 14, 15 and 16 which constitute the radiating and
receiving elements. These shunt slots, as is well known in the art,
may have a dumbbell configuration in order to conserve space and
are alternately disposed on opposite sides of the longitudinal
centerline of the waveguide section 11 by distances selected to
give the requisite amount of coupling for microwave energy.
The waveguide section 11 may be closed at one end 17, and at the
other end has a microwave-acoustical transducer inserted therein
extending between the broad faces of the waveguide section. The
waveguide section 11 together with the shunt slots 12-16
constitutes the instrumentality for receiving and radiating
microwave energy, that is, constitutes the antenna section of the
device, while the microwave-acoustical transducer 18 acts to
convert the acoustical energy received thereby into a modulation of
the microwave energy received by the antenna portion, which
modulated microwave energy is then reradiated by the antenna
section so that intelligence may be derived therefrom at a remote
point.
The detailed structure of the microwave-acoustical transducer can
be best ascertained from the sectional view thereof as illustrated
in FIG. 2. As shown in this figure the transducer comprises a body
19 of cylindrical configuration. A microwave cavity 21, resonant at
the frequency of the microwave energy to be utilized is formed in
one end thereof extending between a partition 22 and a diaphragm
23.
The diaphragm is composed of a very thin sheet of aluminum so that
its lateral displacement by acoustical energy impinging thereon is
relatively great. It has been found that a thickness of 0.0002 inch
is suitable since any lesser thickness approaches the skin
penetration of microwave energy, such penetration being of the
order of 0.0001 inch at the microwave frequency selected as the
most desirable for use. The diaphragm 23 is fastened to the body 19
in untensed condition by means of a retaining ring 24 which may be
fixed to the body by machine screws or any other suitable means,
not shown.
Because of the extreme thinness of the diaphragm 23 and its
untensed or unstretched condition it is necessary to add stiffness
thereto. This is accomplished by irregularly pebbling or embossing
the aluminum sheet which constitutes the diaphragm. At the same
time the embossing must be entirely irregular or random in pattern
since any regularity of such deformation produces a regularity of
pattern of those portions which boarder the deformations and these
portions act in the manner of structural struts which by the nature
of their regularity introduce acoustical resonance characteristics
in the diaphragm mitigating against uniformity of response. On the
other hand random configurations of these deformations avoids
producing any regularities which have inherent acoustic resonances
so that the overall characteristic of the diaphragm is uniform over
a wide range without substantial peaking at any audible
frequency.
A post 26 projects from the center of the wall 22 towards the
diaphragm 23 and the end of the post is spaced from the diaphragm
by a distance of from 0.001 to 0.005 inch. The post 26 is made
conical so that its end 27 has an exceedingly small diameter.
Theoretically, the sharper the end 27 the better since there will
be a greater capacity change in the microwave cavity 21 and it is
in general this change in capacity which constitutes the means for
modulating the microwave energy of the cavity, although some
modulation may also take place by reason of the variation of
concentration of the microwave field between the sharp end of the
post and the diaphragm. Likewise by reason of the sharp post end
there is no air layer entrapped between the end of the post and the
diaphragm which would unduly air load the diaphragm to the
detriment of efficiency and characteristic of response. As a
practical matter, however, the ultimate objectives obtainable by
extreme sharpness cannot be achieved in a commercial device. If the
post is made extremely sharp, say having an end diameter of only a
few Angstrom units, then the spacing between the end of the post
and the diaphragm must also be in the order of Angstrom units and
such close tolerances and fine adjustments are not obtainable as a
practical matter.
In order to obtain the advantages of a sharp post end in a
practical adjustable instrument, therefore, the post 26 is made to
be as sharp as possible and then the end 27 thereof is flattened by
a very small amount so that the extreme end has a diameter of
approximately 0.010 inch. This allows a feasible spacing between
post and diaphragm of from 0.001 - 0.005 inch as heretofore set
forth while still retaining essentially all of the advantages
accruing from using extreme sharpness at the post tip.
Microwave energy is introduced into and the modulated energy
abstracted from the microwave cavity 21 through a circular coupling
orifice 28 which is closed to air and acousitical energy passage by
a dielectric block 29 which may be of polystyrene,
tetrafluoroethylene or other similar substance which permits the
passage of microwave energy.
It is highly desirable that the greatest percentage of modulation
consonant with the greatest amount of energy transfer into and out
of the cavity 21 be obtained. As the coupling is increased,
however, the Q of the cavity is reduced and a reduced Q reduces the
percentage of modulation. Thus there is a critical point at which
any further increase in coupling will so reduce the percentage of
modulation as to reduce the net amount of intelligible signal which
is reradiated. In order to adjust to this critical point so that
the maximum amount of intelligence is reradiated a post 31 is
provided extending from the partition 22 into the coupling orifice
28. By adjusting the distance the post 31 projects into the orifice
28 the required critical coupling can be easily attained.
In order to produce a device giving a flat response over an
extended range of acoustical frequencies it is necessary to air
load the thin, and therefore high compliance, diaphragm 23 to
provide an acoustical impedance match therefor. This may be done by
disposing an air chamber on one side of the diaphragm. Of course,
the microwave resonant cavity will form an air chamber but it has
been found that proper acoustical impedance match requires a larger
chamber than can be provded by the microwave resonant cavity
designed to have small size and hence operating at appropriate
microwave energy frequencies. In order to meet these limiting
conditions the body 19 is recessed to provide an additional chamber
32 and communication for the air mass between the microwave
resonant cavity 21 and the chamber 32 is provided by an annular
circumferential series of holes such as 33 and 34 drilled through
the partition 22. These holes are made of sufficiently small
diameter as to be below the cut-off frequency of the microwave
energy utilized so that no microwave energy leaks into the chamber
32. The microwave resonant cavity, therefore, is composed of the
cavity 21 alone and is designed to be of the proper size for the
frequency of the microwave energy utilized. On the other hand the
acoustic impedance matching chamber includes both the microwave
resonant cavity 21 and the air chamber 32 which is closed by
fastening a plate 36 to the body 19 by any suitable means, not
shown.
As so far described, the cavity 21 and chamber 32 taken together
would form a completely enclosed space impervious to air which
would unduly damp the displacement of the diaphragm producing poor
response, particularly to high frequencies. To obviate this undue
air loading a vent 37 produced by drilling or punching a small hole
in the diaphragm is provided.
In order to provide a means for adjusting the spacing between the
tip 27 of the post 26 and the underside of the diaphragm 23, a set
screw 38 is threaded through a boss 39 formed in the closure plate
36 and the end of this set screw bears against the underside of the
partition 22. Inasmuch as the adjustment of this spacing will be
very small in extent the distortion of the partition 22 by the
force exerted thereagainst by the set screw is sufficient.
In operation, for short distances which do not require a relatively
high level of power return, the microwave-acoustical transducer 18
as depicted in FIG. 2 may be used alone. In other situations where
higher levels of return are desired the microwave-acoustical
transducer is combined with the antenna section 11 as illustrated
in FIG. 1. In either event the microwave energy transmitted from
the remote point is introduced into the resonant cavity 21 through
the microwave transparent window 29 and coupling structure composed
of the orifice 28 and post 31. When the microwave-acoustical
transducer is used alone the energy is so introduced directly from
free space, whereas when this device is used with the antenna
section, the antenna receives the microwave energy from free space
and then introduces it to the microwave cavity in the manner
described. At the same time acoustical energy impinging on the
device results in proportional deflection of the diaphragm 23
varying the capacity between the tip 27 of the post 26 and the
diaphragm 23 to vary the resonance frequency of the cavity 21. This
results in the resonance frequency of the cavity being varied
between points above and below the frequency of the transmitted
microwave and gives rise to at least two different types of
modulation.
In the first instance an amplitude modulation is produced by reason
of the fact that when the cavity 21 is resonant to the frequency of
the impressed microwave energy a relatively large amount of power
is absorbed so that less power is reradiated. As the resonant
frequency of the cavity departs from the frequency of the impressed
microwave energy lesser amounts of power are absorbed and more
power is reradiated.
Secondly and perhaps more important, the impressed energy is phase
modulated by reason of the fact that as the resonant frequency of
the cavity varies from below to above the frequency of the
impressed microwave energy, the cavity changes from an inductive to
a capacitive character producing a large change in phase of the
reflected signal.
After having been so modulated, the energy is retransmitted through
the coupling orifice and post structure and window 29 to free
space, if the microwave-acoustical transducer 18 is used as a
separate element, or to the antenna section 11 to be radiated to
free space by the radiators 12-16 if the combination structure of
FIG. 1 is utilized. In either case the reradiated energy is
modulated over a wide band of acoustical frequencies so that it may
be received at a remote point, appropriately demodulated and the
intelligence information derived therefrom.
In the form of the invention disclosed in FIGS. 3 to 5 the antenna
section performs both the function of a receiver and radiator of
microwave energy and an acoustical load on the microwave-acoustical
transducer to prevent undue acoustical resonance thereof.
Referring to FIG. 3 the device therein disclosed is similar to that
of FIG. 1 in that it comprises an antenna section 41. provided with
shunt receiving and radiating slots 42-46 in its broad face.
Likewise, a microwave-acoustical transducer 47 is inserted in one
end thereof positioned so as to extend between the broad faces of
the waveguide section 41.
In this case, however, since the antenna section 41 also functions
as the acoustical load and path, the end 48 thereof is closed by a
plate 49 provided with a plurality of apertures 51 to allow
acoustical transmission through the waveguide section.
Because it is extremely desirable that the acoustical response be
flat over an extended range, it is necessary that the waveguide
section 41 should not introduce acoustical resonant conditions. The
radiating slots 42 to 46, however, and particularly those adjacent
the microwave-acoustical transducer 47 if left open to the
atmosphere are liable to introduce just such unwanted acoustic
resonance. To prevent such an occurrence a sheet 52 of mica,
tetraflouroethylene or other suitable dielectric is affixed to the
waveguide section 41 over the area occupied by the radiating slots
42 to 46. As a further means of providing a proper acoustic
impedance match between the acoustic path provided by the waveguide
section 41 and the microwave-acoustical transducer 47, the area
occupied by the radiating slots 42 to 46 and lying under the
dielectric sheet 52 is recessed as at 53. Such structure introduces
just the proper amount of acoustic loss in the acoustic path to
prevent acoustic resonance and provides the proper acoustic
impedance match.
The microwave-acoustical transducer 47 used with this form of the
invention is somewhat simpler than that disclosed in FIG. 2 since
no acoustical loading chamber need be provided, this function being
accomplished by the antenna section itself. This form of the
microwave-acoustical transducer may be best understood by referring
to FIG. 4. As therein illustrated the transducer 47 consists of a
cylindrical body 54 recessed to provide a suitable resonant
microwave cavity 56. A diaphragm 57 in all essential details like
that of the diaphragm 23 of FIG. 2, except that it contains no vent
is fastened to the body 47 through the medium of a retaining ring
58, the retaining ring in turn being fastened to the body by any
suitable means such as machine screws not shown. The diaphragm 57
like that of FIG. 2, is composed of a thin sheet of aluminum having
a thickness of approximately 0.0002 inch and similarly is
irregularly embossed for the same reason as heretofore set
forth.
Likewise, a post 59 tapered to a sharp point 61 extends upwardly
from the base of the microwave cavity 56 and is spaced from the
underside of the diaphragm a distance of from 0.001 - 0.005 inch.
Additionally the discussion relative to the sharpness of the tip 61
heretofore set forth with respect to the post 26 of FIG. 2 applies
with equal force and to that end the tip 61 is made to have an
extreme tip diameter pf approximately 0.010 inch.
In order that microwave energy may be coupled into and out of the
microwave cavity 56, a coupling orifice 62 is provided and in this
instance since it is desired that an acoustical path extend from
the diaphragm 57 through the microwave resonant cavity 56 and the
antenna section 41 the orifice 62 is not closed but left open to
the atmosphere.
Again in order that the coupling may be adjusted to such critical
point as to give the largest possible modulated signal return, an
adjustable post 63 extending through the body 54 and into the
orifice 62 is provided.
In operation the modification of FIGS. 3 to 5 functions similarly
to that of FIGS. 1 and 2 insofar as the acoustical modulation of
the impressed microwave energy is concerned. However, because the
acoustical impedance matching structure is incorporated in the
antenna section, the microwave-acoustical transducer 47 cannot
advantageously be utilized when divorced from the antenna
section.
In either modification of the invention an extremely compact but
nevertheless efficient structure is produced. For example, the
antenna section may be a short length of standard waveguide of
exterior 1 .times. 1/2 inch dimensions and either
microwave-acoustical tranducer may be, and is, made of such small
size as to be wholly encompassed within the interior of such
waveguide section.
* * * * *