U.S. patent number 3,678,304 [Application Number 05/105,935] was granted by the patent office on 1972-07-18 for acoustic wave device for converting bulk mode waves to surface waves and vice versa.
Invention is credited to Reginald Frederick Humphryes, Iain McLaren Mason.
United States Patent |
3,678,304 |
Humphryes , et al. |
July 18, 1972 |
ACOUSTIC WAVE DEVICE FOR CONVERTING BULK MODE WAVES TO SURFACE
WAVES AND VICE VERSA
Abstract
An acoustic wave device comprising a body of material having two
generally plane, parallel surfaces facing each other, means for
launching a bulk acoustic standing wave system in the body between
the two surfaces or for detecting such a standing wave system, at
least one of the two surfaces having a shaped profile arranged to
launch a wave having a component consisting of an interface wave on
the boundary of the body and being derived from energy trapped in
the said bulk standing wave system or to receive an interface wave
developed on the boundary of the body and to convert at least part
of it into a bulk standing wave.
Inventors: |
Humphryes; Reginald Frederick
(Rainham, EN), Mason; Iain McLaren (Kiddington, NR.
Woodstock, EN) |
Family
ID: |
26215394 |
Appl.
No.: |
05/105,935 |
Filed: |
January 12, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jan 15, 1970 [GB] |
|
|
2,127/70 |
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Current U.S.
Class: |
310/313B;
310/320; 310/322; 330/5.5; 333/141; 333/150 |
Current CPC
Class: |
H03H
9/17 (20130101); G02B 27/4233 (20130101); H04R
17/08 (20130101) |
Current International
Class: |
G02B
27/42 (20060101); H03H 9/17 (20060101); H03H
9/00 (20060101); H03H 9/145 (20060101); G02B
27/44 (20060101); H04R 17/04 (20060101); H04R
17/08 (20060101); H01v 007/00 () |
Field of
Search: |
;310/8,8.2,8.3,9.5-9.8
;181/.5R,.5AG,.5T,.5FS,.5F,.5H,.5BN ;333/3R,72,3M ;330/5.5,174 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; J. D.
Assistant Examiner: Budd; Mark O.
Claims
We claim:
1. An acoustic wave device comprising a body of piezo-electric
material carrying a pair of contacts on opposite faces of the body
adapted to produce a bulk acoustic standing wave system in the
body, said opposite faces being spaced apart by a distance such as
to produce a resonant structure corresponding to an odd multiple of
a bulk acoustic wave half wavelength, at least one surface of the
body having a shaped profile arranged to launch a wave having at
least a component consisting of an interface wave on a boundary of
the body and being derived from energy trapped in the said bulk
standing wave system, said shaped profile comprising a plurality of
grooves in said surface, said grooves having triangular cross
sections and being placed parallel to one another and perpendicular
to the direction of propagation of interface waves.
2. An acoustic wave device comprising a body of material capable of
supporting acoustic waves and carrying a pair of contacts on
opposite faces of said body spaced apart by a distance such as to
produce a resonant structure corresponding to an odd multiple of a
bulk acoustic wave half wavelength, at least one surface of said
body having a shaped profile arranged to launch a wave having at
least a component consisting of an interface wave on a boundary of
said body and being derived from energy trapped in said resonant
structure.
3. An acoustic wave device as in claim 2 in which said shaped
profile comprises a plurality of perturbations in the surface
repeated regularly at intervals of one interface wavelength.
4. An acoustic wave device as in claim 3 in which each of said
perturbations is asymmetric in cross-section.
5. An acoustic wave device as in claim 4 in which said
perturbations consist of grooves in said surface of said body, said
grooves having triangular cross-sections and being placed parallel
to one another and perpendicular to the direction of propagation of
interface waves.
6. An acoustic wave device comprising a body of material capable of
supporting acoustic waves and carrying a pair of contacts on
opposite faces of said body spaced apart by a distance such as to
produce a resonant structure corresponding to an odd multiple of a
bulk acoustic wave half wavelength, at least one surface of said
body having a shaped profile arranged to receive a wave having at
least a component consisting of an interface wave on a boundary of
said body and operative to convert at least part of said wave into
a bulk standing wave in said resonant structure.
7. An acoustic wave device as in claim 6 in which said shaped
profile comprises a plurality of perturbations in the surface
repeated regularly at intervals of one interface wavelength.
8. An acoustic wave device as in claim 7 in which each of said
perturbations is asymmetric in cross-section.
9. An acoustic wave device as in claim 8 in which said
perturbations consist of grooves in said surface of said body, said
grooves having triangular cross-sections and being placed parallel
to one another and perpendicular to the direction of propagation of
interface waves.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an acoustic wave device. Such a
device may be used for producing in a body of material an acoustic
wave having at least a component consisting of a surface or
interface wave on the surface of the body. It may also be used for
converting an acoustic surface or interface wave into a bulk wave
which may be detected electrically.
In the present specification and claims the expression "interface
wave" will be used to cover both surface waves and interface
waves.
It is known that energy may be trapped in a standing acoustic wave
system set up between small electrodes on opposite faces of a
suitably oriented dielectric plate. Such a system can be arranged
to resonate at frequencies corresponding to odd multiples of a bulk
acoustic wave half wavelength. Resonance corresponds to
constructive interference between bulk waves multiply reflected
between opposite faces of the body. The quality of resonance is a
function of the perfection of reflection from the faces of the
body.
The present invention uses this fact by providing a shaped profile
in at least one surface of the body whereby the quality of
resonance is lowered and reflection losses occur. At least part of
these losses is propagated in the form of an interface wave.
SUMMARY OF THE INVENTION
According to the present invention there is provided an acoustic
wave device comprising a body of material having two generally
plane, parallel surfaces facing each other, means for launching a
bulk acoustic standing wave system in the body between the two
generally plane, parallel surfaces, at least one of the two
generally plane, parallel surfaces of the body having a shaped
profile arranged to launch a wave having at least a component
consisting of an interface wave on the boundary of the body and
being derived from energy trapped in the said bulk standing wave
system.
According to the present invention there is also provided an
acoustic wave device comprising a body of material having two
generally plane, parallel surfaces facing each other, means for
detecting a bulk acoustic standing wave system developed in the
body between the two generally plane, parallel surfaces, at least
one of the two generally plane, parallel surfaces of the body
having a shaped profile arranged to receive an interface wave
developed on the boundary of the body and to convert at least a
part of it into a bulk standing wave.
According to an aspect of the invention there is provided an
acoustic wave device comprising a body of material carrying a pair
of contacts on opposite faces of the body adapted to produce a bulk
acoustic standing wave system in the body, at least one surface of
the body having a shaped profile arranged to launch a wave having
at least a component consisting of an interface wave on a boundary
of the body, and being derived from energy trapped in the said bulk
standing wave system.
Preferably the material comprises piezo-electric material, and the
generally plane, parallel surfaces are spaced apart by a distance
such as to produce a resonant structure corresponding to odd
multiples of a bulk acoustic wave half wavelength. The profile
preferably comprises a plurality of perturbations in the surface
repeated regularly at intervals of one wavelength of the interface
wave, each perturbation preferably being asymmetric in
cross-section.
Examples of materials for producing devices embodying the invention
are quartz, lithium niobate, cadmium sulphide, zinc oxide. Some
variants of the device may be constructed in non-piezo-electric
materials such as sapphire and silicon, provided suitable
arrangements are made for acoustic coupling into the system.
Electrostriction may provide an alternative mechanism for coupling
energy into the system, as may magnetostriction.
A device according to the invention may act as a generator or
receiver of interface waves or may be used as a parametric
amplifier or mixer by the introduction of non-linearity into the
material in which the standing wave system is formed.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described by way of
example with reference to the accompanying drawing in which:
FIG. 1 is a cross-section of an acoustic wave generator,
FIG. 2 is a cross-section of part of an integrated circuit, and
FIG. 3 is a cross-section of a generator combining the principle of
FIG. 1 with a ladder comb generator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 a plate of piezo-electric material 11 carries a
pair of electrodes 12 and 13 on opposite surfaces 14 and 15
thereof. The surfaces 14 and 15 are generally plane and parallel
and facing one another. The thickness of the plate is arranged to
be such that a standing wave system can be set up between the
electrodes 12 and 13 which form a resonant structure corresponding
to odd multiples of the bulk acoustic wave half wavelength.
The surface 14 which carries the electrode 12 has a shaped profile
comprising a series of parallel grooves 16 running across the
surface 14 beneath the electrode 12. The grooves 16 are parallel
and spaced apart at intervals of one Rayleigh wavelength, and each
groove 16 in cross-section has the shape of an asymmetric triangle,
as shown in the figure. The electrode 12 is arranged to fill the
grooves 16.
In operation, the grooves 16 introduce acoustic loss from the
resonator in the form of directionally launched quasi-interface
waves which proceed along the surface 14 in a direction
perpendicular to the grooves 16. The sense in which the interface
waves are propagated in that direction is determined by the
asymmetrical shape of the grooves 16, and in the example shown the
interface wave proceeds in a direction from the steeper sides of
the grooves 16 towards the less steep sides of the grooves.
By way of example, for an energy trapping resonator operating at
100 MHz in the fifth longitudinal wave harmonic, L will be
typically 50 .mu. and the plate thickness d will be (5/2) .times.
50 = 125.mu. thick where L represents the wavelength of a
longitudinal bulk wave. If the grooves 16 are spaced at multiples
of one Rayleigh wavelength (say R = 20.mu. where R is the
wavelength of an interface wave), acoustic loss will be introduced
into the resonator and the quasi interface waves will be launched.
These waves will, in this example, since d = 6R, be
indistinguishable from conventional interface waves. (Viktorovs
criterion.)
It is possible to select the shaped profile in such a manner as to
optimize balance between stored and radiated acoustic energy, and
to minimize generation of spurious bulk waves in the system.
It is possible to construct embodiments of the invention which
provide a number of advantages including narrow bandwidth and high
selectivity, and high generation efficiency together with
conversely high sensitivity to incoming signals. By loading the
shaped resonant face, the sensitivity can be increased at the
expense of bandwidth. The invention may also allow improved
matching to an external circuit.
For example a device has been made in lithium niobate in which the
shaped face comprises a series of parallel grooves having an
asymmetrical triangular cross-section. The steep sides of the
grooves were at right angles to the general surface direction and
the angle at the valley of the groove was 55.degree.. With this
structure the wave launched in the direction from the steeper sides
of the grooves towards the less steep sides of the grooves was 9dB
above the wave launched in the opposite direction.
FIG. 2 is a cross-section of part of an integrated circuit. A
single crystal silicon chip 21 having generally plane parallel
sides carries an integrated circuit shown generally at 23 on one
surface. The integrated circuit includes thin film transducers 25
and 27. The transducer 25 is situated opposite part of the surface
29 which has a profile shaped like the profile 14 in FIG. 1.
Similarly the transducer 27 is situated opposite part of the
surface 31 which has a profile shaped like the profile 14 in FIG.
1.
An electrode 33 is deposited on the part of the surface 29 and an
electrode 35 is deposited on the part of the surface 31. The
surface between the part of the surface 29 and the part of the
surface 31 is treated in known manner to inhibit the propagation of
acoustic interface waves.
The action of the device is as follows. An acoustic interface wave
is propagated from a source not shown towards the electrode 33 and
is there at least partially converted to a bulk acoustic wave. The
bulk acoustic wave is detected by the transducer 25 and processed
in the integrated circuit 23. The resulting signal appears at the
transducer 27 which launches a bulk acoustic wave which, as
described in FIG. 1 above, produces a further interface wave and so
on. Thus integrated circuit components and interface wave
components may be mounted on the same silicon slice.
The introduction of non-linearity into the structure (for example
by means of a stress sensitive p-n junction in the device, or use
of very high amplitude acoustic input) causes it to act as a
parametric amplifier or mixer. In the latter variant, the stability
offered by mechanical resonance proves advantageous for the mixing
of signals from fixed frequency sources such as TV transmitters.
For example an interface wave passed through the device can be
pumped by the acoustic standing wave.
It is also possible to combine a structure according to the present
invention with other acoustic interface wave generating structures,
such as interdigital and ladder comb generators. One such
combination is shown in FIG. 2. The valleys 16 of the surface
deformation are filled in by conducting bars 17 connected
alternately in two sets which are connected one set to each
terminal of a source 18 of alternating voltage. This particular
combination possesses the advantage of giving a nearly
unidirectional acoustic interface wave launch. Insertion
characteristics of the combination will vary with the corrugation
profile.
The device according to the present invention finds application in
the frequency range 0.1 to 500 MHz, the upper limit being set only
by present-day fabrication difficulties.
* * * * *