US3609602A

US3609602A - Acousto-electric signal translation system

Info

Publication number: US3609602A
Application number: US710118A
Authority: US
Inventors: Adrian J De Vries; Fleming Dias
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1968-03-04
Filing date: 1968-03-04
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

A body of piezoelectric material propagates acoustic surface waves. For launching or absorbing those waves, an electrode array is coupled to a surface portion of the body. The array includes a bifilar coil comprising a pair of windings coiled over the surface. A source or load is coupled between one end of one winding and the remote end of the other winding, with the remaining ends of both windings coupled together. The spacing between adjacent turns of the windings is effectively one-half the wavelength of the acoustic waves at the operating frequency. The bifilar winding is shown either in a form where it is coiled around a cylinder or where it is nested concentrically on a surface. In one species, an input transducer launches waves in two directions around a cylinder, and an output transducer absorbs waves coming from both of the two directions. The bifilar coil contributes an inductive reactance to compensate the clamped capacitance of the transducer.

Description

United States Patent [72] Inventors Adrian J. De Vries Elmhurst;

Fleming Dias, Chicago, both of III. [21] Appl. No. 710,118 [22] Filed Mar. 4, 1968 [45] Patented Sept. 28, 1971 [73] Assignee Zenith Radio Corporation Chicago, Ill.

[54] ACOUSTO-ELECTRIC SIGNAL TRANSLATION SYSTEM 7 Claims, 3 Drawing Figs.

[52] [1.8. CI 333/72, 33 3/30 [51] Int. Cl 03h 9/00 [50] Field ofSearch 333/30, 72; 3 30/4.9

[56] References Cited UNITED STATES PATENTS 3,187,192 6/1965 Nalos 330/4.9 3,300,739 l/1967 Mortley. 333/72 3,401,360 9/1968 Du Bois. 333/30 3,360,749 12/l967 Sittig 333/30 3,369,199 2/1968 Sittig 333/30 Primary ExaminerHerman Karl Saalbach Assistant ExaminerC. Baraff Attorneys-Francis W. Crotty and Hugh H. Drake ABSTRACT: A body of piezoelectric material propagates acoustic surface waves. For launching or absorbing those waves, an electrode array is coupled to a surface portion of the body. The array includes a bifilar coil comprising a pair of windings coiled over the surface. A source or load is coupled between one end of one winding and the remote end of the other winding, with the remaining ends of both windings coupled together. The spacing between adjacent turns of the windings is effectively one-half the wavelength of the acoustic waves at the operating frequency. The bifilar winding is shown either in a form where it is coiled around a cylinder or where it is nested concentrically on a surface. In one species, an input transducer launches waves in two directions around a cylinder, and an output transducer absorbs waves coming from both of the two directions. The bifilar coil contributes an inductive reactance to compensate the clamped capacitance of the transducer.

PATENIEUSEP28I9H 3.609.602

Inventors Adrian J. De Vries Fleming Dias ACOUSTO-ELECTRIC SIGNAL TRANSLATION SYSTEM This invention pertains to signal translation systems. More particularly, it relates to solid-state circuitry including an acoustoelectric transducing arrangement which involves interaction between transducer elements coupled to a piezoelectric material and acoustic waves propagated in that material.

In copending application Ser. No. 582,387, filedSept. 27, 1966 now abandoned, there are disclosed and claimed a number of different embodiments of acoustoelectric devices in which acoustic surface waves propagating in a piezoelectric material interact with transducers coupled to the surface waves. In each of the embodiments particularly disclosed in that application, surface waves launched in the body of piezoelectric material are caused, in one manner or another, to interact with a second transducer spaced along the surface from the first. In the simplest case, the firsttransducer is coupled to a source of signals while the second transducer is coupled to a load, the signal energy being translated by the acoustic waves between the two transducers.

In operation, the transducers exhibit a clamped capacitance which may be determinative of the magnitude of impedance the transducers are capable of presenting to the associated circuitry. The clamped capacitance may be defined as that capacitance exhibited when all mechanical motion is inhibited. When utilizing these devices, that clamped capacitance heretofore has been tuned out or compensated by the use of external inductors.

It is the general object of the present invention to provide a new and improved signal translation system of the aforesaid acoustoelectric variety and in which the clamped capacitance is compensated without the need for external elements.

It is another object of the present invention to provide a new and improved acoustoelectric signal translation system of the foregoing character which is capable of being fabricated with either a curved or a planar surface over which the waves are translated.

A further object of the present invention is to provide a new improved signal translation system in which acoustic waves launched in two different directions by an input transducer are effectively absorbed and utilized by an output transducer.

A related object of the present invention is to provide such a device in which interference from acoustic waves launched in a second direction is avoided.

In accordance with one aspect of the present invention, an acoustoelectric signal translation system includes a source of signals at a predetermined frequency and a body of piezoelectric material propagative of acoustic surface waves along the body. The array includes a bifilar coil comprising first and second windings coiled over the surface with the two windings interleaved. The signal source is coupled between one end of one of the windings and the remote end of the other winding while the remaining ends of both windings are coupled to one another. The center-to-center spacing of adjacent turns of the bifilar coil is effectively one-half the wavelength of the acoustic waves at the desired signal frequency. Finally, the system includes interaction means coupled to a second portion of the body spaced from the first and responsive to the launched acoustic waves for utilizing the signal energy translated thereby.

With regard to another aspect of the present invention the transducer disposed on the first portion of the piezoelectric body responds to input signals and launches acoustic waves respectively along each one of a pair of paths individually extending in different directions from the transducer. Interaction means, coupled to the second portion of the body and disposed in both of the aforesaid paths, responds simultaneously to the acoustic waves launched in both paths to utilize the signal energy translated by such waves.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawing, in the several figures of which like reference numerals identify like elements and in which:

FIG. 1 is a diagram of one embodiment of a signal translation system embodying the invention;

FIG. 2 is a diagram of an alternative embodiment of such a system; and

FIG. 3 is a diagram of yet another alternative embodiment of such a signal translation system.

In FIG. 1, a signal source 10 is coupled between terminals 11 and 12 of an input transducer 13. Transducer 13 is coupled to the major surface of a piezoelectric body 14 in this case in the shape of an elongated cylindrical rod. The transducer is constructed of a bifilar coil comprising first and second windings l5 and 16 coiled over the surface of body 14 with their individual turns distributed thcrealong so as to constitute an electrical array. By way of terminal 11 and 12, source 10 is coupled between one end of winding 15 and the other or remote end of winding 16. The remaining end of winding 15 has a terminal 17, and the remaining end of winding 16 has a terminal 18, and terminals l7, 18 are coupled together, in this case by both being connected to ground. Further, the centerto-center spacing of adjacent turns of the set of

windings

15 and 16, that is to say the center-to-center spacing of adjacent turns of the bifilar coil, is one-half of the designed acoustic wavelength, in the material of body 14, of the signal wave for which it is desired to achieve maximum response.

windings

15 and 16 are formed of a material such as gold which may be vacuum deposited, or plated and then etched, upon the exterior surface of a polished piezoelectric body of a a material such as PZT (lead zirconate titanate) or other piezoelectric material having similar properties.

When PTZ is used as the piezoelectric material, it preferably is polarized so that the cylindrical axis of body 14 is the axis of electrical symmetry. This may be accomplished by polarizing the material either radially or in the direction of the cylindrical axis. For radial polarization, a rod-type electrode is embedded in the rod with its axis coinciding with the cylindrical axis of body 14, and the other polarizing electrode is formed by depositing a conductive layer on the external cylindrical surface of body 14; that layer is removed following polarization. Axial polarization may be achieved by affixing the polarizing electrodes to opposing ends of body 14.

PTZ is particularly attractive as the material for body 14 because its high permittivity (about 1,000) permits the use of comparatively small coils in transducer 13 to achieve the results to be further described. Alternatively, zinc oxide may be used; its so-called c-axis is oriented to be parallel with the cylindrical axis of body 14.

With the described arrangement transducer 13 is composed of interleaved conductive stripes to which source 10 feeds alternating electric potentials. It is known that a transducer of that general nature, when coupled to a piezoelectric medium, produces acoustic surface waves on the medium which, in the simplified isotropic case of a ceramic poled perpendicularly to the surface, travel at right angles to the stripes. Thus, in operation, direct piezoelectric surface wave transduction is accomplished by the spatially periodic interdigital electrodes of transducer 13 and specifically by the periodic electric fields created between those electrode stripes in response to a signal from source 10 of a frequency such that the wavelength of the acoustic waves corresponds to the center-to-center spacing of two adjacent turns belonging to the same one of the

interleaved windings

15,16. This piezoelectric coupling to the surface waves occurs when the strain components produced by the electrical fields in the piezoelectric material are substantially matched to the strain components associated with the surface wave mode. Source 10, for example the front end of a television receiver, may produce a range of LP. signal frequencies for application to IF amplifier and video system 21. However, by reason of the selective nature of transducer 13, only a narrow range of frequencies corresponding to the desired IF bandwidth are converted to surface wave energy. The result is that transducer 13 and piezoelectric body 14 constitute a filter.

The kind of waves produced by transducer 13 generally may be described as being in the known Rayleigh wave mode. However, waves so traveling over a curved surface are not pure Rayleigh waves but when the diameter of body 14 is large relative to the acoustic wavelength, the surface may be considered to be essentially flat and the wave action approaches that of the Rayleigh condition.

Because it is composed of spaced elements of conductive material separated by a dielectric, transducer 13 exhibits, as seen across terminals 11 and 12, that which has been described as the clamped capacitance. By connecting the windings as described and illustrated, not only is the desired electric field created between adjacent turns so as to launch the surface waves, but the magnetic flux lines encircled by the turns are in a direction to reenforce one another. Consequently, the bifilar winding arrangement also develops compensating inductance which appears between terminals 1 1 and 12. More particularly, the clamped capacitance of transducer 13 is distributed along the interleaved windings. To achieve compensation of that 21. At The number of turns of bifilar coil 13 and the pitch of the coil turns are selected to contribute an amount of inductive reactance for compensation purposes compatible with the desired bandwidth of the transducer. In other words, this in practical structures is a matter of compromise although ideally the input impedance, presented across terminals 11 and 12, is real at the frequency of maximum response of the electroacoustic array.

The acoustic waves launched by transducer 13 may be absorbed and utilized directly and for that purpose FIG. 1 incorporates a second transducer structurally similar to transducer 13 and responsive to the acoustic waves. Thus, an output transducer 20 likewise is formed by coiling a bifilar winding around the other end portion of the cylindrical rod 14 of piezoelectric material. A load 21 is coupled between one end 22 of one winding 25 of the output transducer coil. The remaining end 27 of winding 23 is coupled to the remaining end 24 of winding 25 by virtue of their common connection to ground. AS before, the center-to-center spacing between adjacent turns of the bifilar winding in output transducer 20 is one-half of the acoustic wavelenghth in the piezoelectric material of the signal wave for which maximum response is desired. In operation, transducer 20 absorbs energy from the surface waves launched by transducer 13 and feeds it to load 21. At the same time, the winding arrangement is such that it creates an inductive reactance which is employed to compensate fully or partially the clamped capacitance of transducer 20. The winding turns in transducer 13 are parallel to those in transducer 20.

The FIG. 2 embodiment is similar in that it includes an input transducer 30 which launches surface waves along a piezoelectric substrate 31 to an output transducer 32. In this case, however, the wave propagating surface of substrate 31 is planar and transducers 30 and 32 are composed of bifilar coils comprising a pair of windings having a flat or pancake eonfiguration with winding turns nested concentrically on the surface of substrate 31. For convenience, the input signal source and the load have been omitted from FIG. 2 but, as in the case of FIG. 1, those devices are coupled between one end of one winding and the remote end of the other winding while the remaining ends of both windings are coupled together. Thus, the input signal energy may be applied between the terminal 33 of one winding 34 and the remote terminal 35 of the other winding 36. The remaining two terminals 370 and 37b are then coupled together to complete the circuitry. Similarly, the signal energy derived from transducer 32 is taken across a terminal 38 of one winding 39 of the bifilar coil and the remote terminal 40 of other winding 41 of the bifilar coil. As before, the remaining

terminals

42a and 42b of winding 39, 40 are coupled together. Transducers 30 and 32 may be formed by vacuum depositing or plating and, as is often done when printing circuits, the terminals may be formed merely by depositing I or leaving an enlarged area integral with the strips and to which the connections are made.

In the case of either transducer 13 in FIG. 1 or transducer 30 in FIG. 2, the potentials developed between adjacent turns of the windings produce a dominant pair of waves traveling longitudinally along the surface of the piezoelectric material in opposing directions perpendicular to the stripes for the illustrated isotropic case and a minor pair of waves traveling normally to the first. A fraction of the dominant waves pass through the output transducer. Accordingly, in the devices of FIGS. 1 and 2 it may be desirable to include means for attenuating the nonutilized one of the dominant waves, or the wave passed by the output transducer, and also the minor pair of waves in order to prevent unwanted subsequent interaction with reflected waves. To this end, all peripheral portions of the piezoelectric material may be formed to have an irregular contour, as indicated and as a result of which the waves are scattered and consequently attenuated in a plurality of noncoherent reflections.

In the embodiment of FIG. 2, each transducer 30, 32 may be thought of as having equal and separated left and right portions as viewed in the drawing with the dividing line of such portions perpendicular to the propagation direction. It is desirable that surface waves generated by the left portion of the transducer be enhanced by surface waves generated by the other or right portion of the same transducer. The general condition to be This loss is that turns belonging to the same winding, for instance winding 34 of transducer 30, are positioned such bifilar the center-to-center spacing of successive turns of that winding is a full wavelength of the acoustic wave. It may also be noted that, for increased selectivity, additional electrode turns may be added to the bifilar transducer. Still additionally, in the arrangement of FIG. 2 some energy is lost by reason of the generation of waves heretofore referred to as the minor pair traveling in directions perpendicular to a line joining the input and output transducer. Thisloss may be reduced by forming the coils to have a large aspect ratio, that is, to form the bifilar coils to have a width, perpendicular to the direction of desired wave travel, large compared to .the dimension in the direction of wave travel.

Another approach with respect to the second of the two acoustic waves launched by an input transducer is that of FIG. 3 which actually utilizes both of the pair of dominant waves simultaneously. To this end, an input transducer 50 is disposed on the exterior cylindrical surface portion of a piezoelectric element 51 which is cylindrical in shape. Diametrically opposite input transducer 50 is an output transducer 52. Consequently, the dominant pair of acoustic surface waves developed by transducer 50 in response to input signals are launched respectively along each one of a pair of

paths

53 and 54 which extend individually in different directions from transducer 50. Output transducer 52 is disposed in both of

paths

53 and 54 so as to respond simultaneously to the acoustic waves traveling along both paths.

Transducers

50 and 52 may be placed upon either the interior or exterior curved surfaces of cylindrical element 51. The exterior curved surface is preferred because it is known that surface waves propagating over interior curved surfaces suffer attenuation by virtue of conversion to bulk waves. In either case, the winding turns are nested concentrically on the surface and the bifilar coil as a whole is given a slight curvature so as to lie flat against the curved surface of the piezoelectric element. Consequently,

transducers

50 and 52 are of essentially the same general configuration as in FIG. 2 with the winding turns nested concentrically upon a surface of element 51. The input signal source and the load, as well as the individual winding connections to each of

transducers

50 and 52, which have not been shown, are the same as described above with respect to FIG. 2.

As indicated in FIG. 3, a cylindrical metallic core 55 may advantageously be provided for piezoelectric element Sl. It may serve, for example, as one of the pair of electrodes required to polarize element 51. After the polarizing has been accomplished, the other ore external electrode (not shown) of the pair is removed and the inner one 55 is retained to constitute an electrostatic shield between

transducers

50 and 52. It may also aid in physically supporting the acoustic system in its operating relation to other devices. If desired, the surface portions of element which support

transducers

50 and 52 may be flattened to facilitate mounting the transducers.

The arrangements disclosed permit the formation of surface wave transducers in a manner inherently creating an inductive reactance useful in compensating the clamped capacitance necessarily associated with the use of a plurality of spaced electrodes. The principle involved is applicable to transducing arrangements of either a curved or a generally fiat configuration, thus giving rise to a wide variety of different device configurations. Being entirely of a solid state nature, the arrangements discussed likewise lend themselves admirably to complete integration of circuitry and device. in addition the overall arrangement of FIG. 3 permits positive positive utilization of both the dominant waves necessarily developed by an acoustic wave transducer of the array type.

While particular embodiments of the present invention have i been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Accordingly, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. An acoustoelectric signal translation system comprising:

a source of signals of a predetermined frequency;

a body of piezoelectric material propagative of acoustic surface waves;

a first electrode array coupled to a first surface portion of said body and responsive to said signals for launching acoustic surface waves along said body, said array including a bifilar coil comprising interleaved first and second windings coiled over said surface with said source coupled between one end of one of said windings and the remote end of the other of said windings, the remaining ends of said windings being coupled to one another, and

I the spacing between adjacent turns of said bifilar coil being effectively one-half the wavelength of the acoustic waves at said predetermined frequency;

and interaction means coupled to a second portion of said body spaced from said first portion, responsive to said launched acoustic waves for deriving the signal energy translated thereby.

2. A system as defined in claim 1 in which said interaction means includes:

a second electrode array including another bifilar coil comprising interleaved third and fourth windings coiled over said surface with the spacing between adjacent turns of said other bifilar coil being effectively one-half the wavelength of the acoustic waves at said predetermined frequency;

a load coupled between one end of said third winding and the remote end of said fourth winding;

and means for connecting the remaining ends of said third and fourth windings to the remaining ends of said first and second windings.

3. A system as defined in claim 1 in which said body is of elongated cylindrical shape and said bifilar coil is coiled around the cylindrical surface of said body.

4. A system as defined in claim 1 in which said body includes a generally planar surface on which said transducer is disposed with said bifilar coil of generally flat configuration and having the winding turns thereof nested concentrically on said surface.

5. A system as defined in claim 1 in which said body is of cylindrical shape and said bifilar winding has its turns nested concentrically on an outer peripheral surface of said body to launch said acoustic waves along a curved path over said surface.

6. A system as defined in claim 1 in which said bifilar coil contributes inductive reactance substantially compensatory of the clamped capacitance created by said windings and said body.

7. An acoustoelectric signal translation system comprising:

a generally cylindrical body of piezoelectric material propagative of acoustic waves;

a surface wave transducer disposed on a first peripheral portion of said body and responsive to input signals for launching acoustic surface waves respectively along each one of a pair of circumferential paths individually extending in opposite directions from said transducer;

and interaction means, comprising a second surface wave transducer coupled to a second peripheral portion of said body spaced from said first peripheral portion and disposed in both of said paths, responsive to said launched acoustic surface waves in both paths for utilizing the signal energy translated thereby, in which said body is a hollow cylinder and in which a conductive metallic core extends axially through said body to serve as a shield between said transducers.

Claims

2. A system as defined in claim 1 in which said interaction means includes: a second electrode array including another bifilar coil comprising interleaved third and fourth windings coiled over said surface with the spacing between adjacent turns of said other bifilar coil being effectively one-half the wavelength of the acoustic waves at said predetermined frequency; a load coupled between one end of said third winding and the remote end of said fourth winding; and means for connecting the remaining ends of said third and fourth windings to the remaining ends of said first and second windings.
3. A system as defined in claim 1 in which said body is of elongated cylindrical shape and said bifilar coil is coiled around the cylindrical surface of said body.
4. A system as defined in claim 1 in which said body includes a generally planar surface on which said transducer is disposed with said bifilar coil of generally flat configuration and having the winding turns thereof nested concentrically on said surface.
5. A system as defined in claim 1 in which said body is of cylindrical shape and said bifilar winding has its turns nested concentrically on an outer peripheral surface of said body to launch said acoustic waves along a curved path over said surface.
6. A system as defined in claim 1 in which said bifilar coil contributes inductive reactance substantially compensatory of the clamped capacitance created by said windings and said body.
7. An acoustoelectric signal translation system comprising: a generally cylindrical body of piezoelectric material propagative of acoustic waves; a surface wave transducer disposed on a first peripheral portion of said body and responsive to input signals for launching acoustic surface waves respectively along each one of a pair of circumferential paths individually extending in opposite directions from said transducer; and interaction means, comprising a second surface wave transducer coupled to a second peripheral portion of said body spaced from said first peripheral portion and disposed in both of said paths, responsive to said launched acoustic surface waves in both paths for utilizing the signal energy translated thereby, in which said body is a hollow cylinder and in which a conductive metallic core extends axially through said Body to serve as a shield between said transducers.