US3070775A - Electroacoustic piezoelectricpaste transducer - Google Patents

Description

INVENTOR.

2 Sheets-Sheet 1 DAN/EL E. ANDREWS, JR.

Dec. 25, 1962 D. E. ANDREWS, JR

ELECTROACOUSTIC PIEZOELECTRIC-PASTE TRANSDUCER Filed Oct. 16, 1959 F /'g. I

POLARIZING VOLTAGE SOURCE SIGNAL INPUT ON TRANSMIT SIGNAL OUTPUT 0N RECEIVE 1962 D. E. ANDREWS, JR 3,070,775

ELECTROACOUSTIC PIEZOELECTRIC-PASTE TRANSDUCER Filed Oct. 16, 1959 7 2 Sheets- Sheet 2 Fig. 4

Fig. 5 46 IN VEN TOR. DAN/E L E. ANDREWS, JR.

United States Patent Office 3,070,775 Patented Dec. 25, 1962 3,070,775 ELECTROACOUSTIC PIEZOELECTRIC- PASTE TRANSDUCER Daniel E. Andrews, Jr., 3657 Promontory St., San Diego 9, Calif.

Filed Oct. 16, 1959, Ser. No. 847,028 35 Claims. (Cl. 340-) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to energy converters and more particularly to a reversible broadband transducer which converts electrical energy into acoustical energy and vice versa and which may be physically characterized as expedient to conform with its environmental requirements.

In the past, electroacoustic transducers have included various and sundry substantially rigid energy conversion elements such as tubes, rods, bars, and sheets of magnetostrictive or piezoelectric materials. Because these elements have inherent resonance characteristics which remain substantially constant, their operational bandwidths are severely limited whether they are used individually or in some concerted arrangement. Moreover, the acoustical impedance match between the transducers using these materials and their operational media such as water, other fluids, rubber, plastics, and living tissue is very poor as a result of considerable differences in their densities and respective sound transmission properties. Also, in view of the fact that these transducers are of necessity substantially rigid in structure, they do not lend themselves to being bent or formed according to desired body contours. In addition, they are quite subject to shock and vibration damage which, in turn, ordinarily requires skilled technicians for repair purposes.

The present invention, although relatively simple in structure, is highly effective from both the structural and functional standpoints in that its operation is dependent only on the use of electrically conductive electrodes being immersed in a piezoelectric-paste substance and encased in a flexible, acoustically transparent container in such manner that paste leakage and contamination and electrode shorting is prevented. Accordingly, it can readily be seen that since the energy converter element is of a paste or slurry type mixture and the container is flexible, the subject transducers assembled structural configuration is readily adjustable to make it conform to many desired forms or profiles without adversely affecting its functional qualities. Obviously, this would increase the number of places and circumstances where its use would be advantageous over the rigid structure of the prior art.

Perhaps of even more importance, however, is the fact that the transducer of this invention is not subject to inherent resonance characteristics which limit its frequency range of operation excessively. On the contrary, the energy converter element being a homogenous mixture of any suitable electrically non-conductive liquid or liquids and ground or finely-divided piezoelectric material enables the .specific acoustic impedance thereof to be adjusted over a wide range of frequency values, depending on the selection and proportions of the materials used. This, of course, greatly facilitates acoustical impedance matching to most fluids, rubbers, plastics, and living tissue, resulting in a more efficient transducer which requires less power to operate for many practical purposes, regardless of whether it is acting as an energy wave transmitting element or an energy wave receiving element.

It is, therefore, a primary object of this invention to provide a reversible transducer with broadband operational characteristics.

Another object of this invention is to provide an improved transducer having a pliable, adjustable, formable structure which may be adapted to various installation configurations.

A further object of this invention is to provide an improved transducer which is less subject to shock and vibration damage.

Another object of this invention is to provide an acoustical transducer with adjustable impedance characteristics.

Another object of this invention is to provide an improved acoustical transducer with adjustable operable range characteristics.

Another object of this invention is to provide an energy converter which is less susceptible to inherent resonant frequency characteristics.

A further object of this invention is to provide a reversible transducer with improved acoustical impedance matching characteristics.

Last but not least, it is an object of this invention to provide an electroacoustical transducer which may be economically manufactured and easily maintained.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view with parts broken away of a blanket-type piezoelectric-paste transducer combined with .a box diagram of an exemplary polarizing voltage source.

FIG. 2 is a perspective view with parts broken away of a scroll-type piezoelectric-paste transducer.

FIG. 3 is a perspective view with parts broken away of a laminated-disc type piezoelectric-paste transducer.

FIG. 4 is a schematic diagram of an exemplary polarizing voltage source with a series feed circuit which may be combined with the piezoelectric-paste transducers of this invention for both receiving and transmitting operation.

FIG. 5 is a schematic diagram of an exemplary polarizing voltage source with a shunt feed circuit which may be combined with the piezoelectric-paste transducers of this invention for both receiving and transmitting operation.

FIG. 6 is a schematic diagram of an exemplary polarizing voltage source with a direct coupled feed circuit which may be combined with the piezoelectric-paste transducer of this invention for transmission operation only.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 ablankettype piezoelectric transducer 11 having a flexible pair of spacially disposed, electrically conductive electrodes 12 of metal screen or foil material separated by an electrically non-conductive flexible insulator screen or lattice 13 of plastic or other suitable porous insulating material. The space between said electrodes not occupied by said insulator screen is completely filled with a piezoelectricpaste 14 made up of ground or powdered piezoelectric materials which may be homogenously mixed with any suitable non-conductive liquid or liquids. For example, appropriate piezoelectric materials could include finely divided crystals of tourmaline, quartz, Rochelle salt, tartic acid, ammonium di-hydrogen phosphate, and barium meta titanate, or any combination thereof which may be found to be expedient for producing the desired converter and impedance characteristics. In order to insure optimum flexibility and formability of said piezoelectric paste, the aforesaid non-conductive liquid is mixed therewith. Although many liquids would perform this function satisfactorily, it has been found that conventional silicon fluids such as, for example, the organosilicons and the organopolysiloxanes or silicones ([(CH SiO],,), transformer oil, and castor oil are well suited therefor. It has also been found desirable in some instances to incorporate a binder in the piezoelectric paste. Theselection of the maten'als to be used as a binder depends on the resiliency of the paste desired. When, for instance, considerable flexibility is preferred, a rubber or resilient resinous plastic compound binder may be used. On the other hand, a rigid, hardened binder of suitable plastic material or otherwise may be used in event it is desired to make the paste relatively rigid and inflexible in order to achieve some specific operational objective.

The entire assembly mentioned thus far is enclosed in a a resilient case or bag which is substantially transparent to acoustical energy. Again, many materials are appropriate for the manufacture of this bag; however, flexible rubber or rubber-like plastic materials are eminently satisfactory when used in the proper thickness for optimum transfer of energy between the converter assembly and the medium Within which the transducer is operating. 7 Connected to each of electrodes 12 are electrical leads 16 which pass through sealed exits of case 15 in such manner that the fluid in which the transducer is operating cannot penetrate therethrough to contaminate or short the piezoelectric paste converter assembly. These electrical leads are also connected to a voltage polarizing circuit' l7 of any conventional type suitable for any predetermined driving or receiving operation or both.

When piezoelectric crystals are placed between a pair 'of metal foils and subjected to mechanical stress, they show a separation of electrical charge, some regions becoming positively charged and others negatively charged. .A change from tensile to compressive stress reverses the polarity. Conversely, if an alternating potential difference is applied to the metal foils, the crystal-alternately expands and contracts with the alternating electric field. In the present invention the piezoelectric crystals have been ground or powdered into subcry'stals or microcrystals and combined with a suitable non-conducting liquid in order to achieve a broad-band piezoelectric material of moderately low and adjustable acoustical impedance. A polarizing voltage may be employed in conjunction with this paste-type transducer in order to obtain proper microcrystal alignment in lieu of the mechanical type alignment attainable .in foiled-crystal transducers belonging to the prior art. This arrangement consequently effects a unique combination of conventional and nonconventional structural elements to produce a highly useful result, viz., producing an output signal of the same frequency as the input signal.

. Although for some purposes it may not be necessary to usea voltage polarizing source in conjunction with the subject piezoelectric paste-type transducer, it has been ';found that elimination thereof may change the frequency of the Wave energy transferred by the converter unit. For

' instance, when a 1000 cycle per second voltage was impressed across the transducer without polarization, a 2000 cycle per second audible toneas well as a low intensity 1000 cycle per second tone was emitted therefrom, but "when a DC. polarizing voltage'was applied in series with .the AC. driving voltage, the double frequency effect disappeared and the output frequency was the sameas the frequency of the input. Thus it can be seen that a unique cooperation exists between the subject piezoelectric-paste transducer and the. polarizing voltage source due to the' fact that said paste contains a plurality of piezoelectric particles which should be aligned appropriately for optimum operation at any given frequency.

Electrical leads 18 'are connected to appropriate trans- V mitters and receivers tnot shown) to respectively obtain 7 an input intelligence signal therefrom on transmission and I provide an output intelligence signal thereto on reception. Referring now to FIG. 2, a scroll-type modification 19 oft-he piezoelectric paste transducer of this invention is like, an insulator screen 21 of plastic, rubber, or other suitable electrically non-conductive material sandwiched V in between each of said electrodes, and a piezoelectric paste material 22 comparable to that of FIG. 1 disposed to fill that space between said electrodes not occupied by insulator 21. Encasing the converter assembly containing the aforementioned elements is an acoustically transparent sheath, jacket, or bag 23 which may also be made of a thin layer of rubber, plastic, or other resilient material. Although many materials are available which meet the required physical characteristics of this sheath for practical purposes, insofar as it is possible, a material should be selected which has an elasticity that approaches the elasticity of the medium in which the entire transducer is operating in order to have optimum elficiency during wave energy'transfer. Of course, it is noteworthy that the electrodes and the insulators are in tubular form and extend alternately in coaxial layers from some predetermined inner radius to some desired outer radius with the sheath acting as the entire external surface. Every other electrode of said plurality of electrodes is connected in parallel to electrically form two large electrodes having considerably more surface area than any one electrode would have alone, with one of said electrodes being positive and the other being negative according to the way Electrical leads 24 are appropriately connected to the positive and negative parallel connected sets of electrodes within the subject transducer and extend through sealed apertures in said acoustically transparent sheath for further connection to a co-acting polarizing voltage circuit or pertinent receivers and transmitters, as the'case may be, or both.

Another embodiment 25 of the piezoelectric paste transducer of this invention is depicted in FIG. 3. An electrically non-conductive end cap 26 supports an electrically non-conductive mast or rod 27 at one end which, in turn, supports metallic screen or foil discs 28 with screen or gauze type insulators 29 of any suitable insulating material such as plastic, rubber, or the like, disposed therebetween along the longitudinal axis of the mast. Another electrically non-conductive end cap may be attached to the other end of said mast for support of FIGS. 1 and 2. All of these elements are encased in a" container 31 which is resilient and made of such material to be substantially clear to acoustical wave energy and which is open at one end, making it adaptable to receive a header 32 which may be screwed thereon or mounted in any other conventional manner for leakproof operation. Mounted on said header is a packing-gland assembly 33 through which an electrical cable 34 havingv leads 35 passes. I

The alternate discs areall connected in parallel, resulting in two electrodes with considerable surface area.

These electrodes are each connected to one of the leads of cable 34 adapted for subsequent connection to other cooperating apparatus such as polarizing voltage sources, transmitters, receivers, etc.

It should be understood that as little or as much piezoelectric paste as desired for any specific operating condition may be used in any of the aforementioned embodiments, but ordinarily the entire container will be filled therewith, with the exception, of course, of that portion occupied by the electrode and insulator elements, electrical leads, and support members, if any. This arrangement results in a compact unit which efficiently produces wave energy transfer to and from any pertinent ambient environmental medium, regardless of what it may be.

Referring now to FIG. 4, a series fed polarizing voltage source 36 is shown having signal input-output terminals 37 connected to one winding of a transformer 38. The other winding of transformer 38 is connected in series to a supply of polarized voltage 39, such as, for example, a battery or the like, and adapted to be connected to the subject piezoelectric paste transducer at terminals 40.

FIG. 5 depicts a shunt fed polarizing voltage source 41 having signal input-output terminals 42 adapted to be connected to the piezoelectric paste transducer at terminals 43 through a capacitor 44. A polarized voltage supply 45 in series connection with a choke 46 is parallel coupled across terminals 43.

FIG. 6 illustrates a direct coupled polarizing voltage source 47 which may be used in combination with the subject piezoelectric paste transducer when it is employed as a sound source. Shown is a triode tube 48 having a plate, a grid, and a cathode with said plate having B+ voltage applied thereto through a resistor 49, and said cathode being connected to ground through a resistor 50 and a capacitor 51 in parallel therewith. The input intelligence signal is applied at terminals 52 from which it is applied to the grid of the aforesaid triode tube through a capacitor 53. Grid bias resistor 54 interconnects said grid and ground. The output is obtained from terminals 55, one of which is grounded and the other of which is coupled to the plate of said triode. When terminals 55 are connected to the electrical leads of the subject piezoelectric paste transducer, the DC. plate voltage serves as the polarizing voltage While the AC. signal at the plate serves as the driving voltage.

Briefly, this invention operates in the following manner. When the transducer is being used as a sound source, the intelligence signal is applied to the polarizing voltage source from which it is conveyed along with the polarizing voltage to the piezoelectric paste transducer. Upon reaching the transducer, the piezoelectric material expands and contracts according to its normal electrophysical characteristics and in proportion to the amplitude of the intelligence signal. Since, in this case, the expanding and contracting movement takes place in each piezoelectric particle, the total piezoelectric paste movement in any one direction is approximately the sum of the movements of all particles in said direction. As the entire paste expands and contracts the sheath, being resilient, expands and contracts therewith. Consequently, whenever the transducer is placed in a ponderable elastic fluid medium such as water, the medium is, in turn, moved by the external surface of the sheath, causing compression thereof during expansion and rarefaction thereof during contraction. Thus, it can be seen that intelligence can be transmitted through said medium by means of the pressure waves produced by the subject transducer. And, due to the fact that it has only a negligible inherent resonant frequency, if any, said intelligence may be broadcast over a broad band of frequencies.

With the exception of a combination using the polarizing voltage source of FIG. 6, all other combinations are reversible, in that an energy wave received by the transducer from its environmental medium results in an electrical signal at the output terminals of the polarizing voltage source. A combination using the feed circuit of FIG. 6 obviously can only convey electrical signals in one direction due to the inherent operational characteristics of an electron tube.

It should be understood, of course, that the foregoing disclosure relates only to the preferred embodiments of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A piezoelectric paste transducer system comprising in combination a plurality of spacially disposed electrically conductive electrodes, flexible means placed between said electrodes for insulating same from one another, means surround-ing said electrodes and said insulating means for containing same as a unitary package, a piezoelectric paste disposed Within said containing means for filling substantially all unoccupied volume therein, electrical leads appropriately connected to said electrodes for transmitting signals therefrom and thereto, and means connected to said electrical leads for supplying a polarizing voltage to said piezoelectric paste.

2. A piezoelectric paste transducer system comprising in combination means for supplying a polarized voltage, a plurality of flexible electrodes, resilient insulator means disposed between said electrodes, a substantially acoustically transparent container surrounding said flexible electrodes and resilient insulator means, a piezoelectric paste disposed within said container in contact with the entire inner surface thereof and the outer surfaces of said electrodes and insulator means, and means interconnecting said polarized voltage supply means and said electrodes for supplying a polarized voltage to said piezoelectric paste.

3. The device of claim 2 wherein said flexible electrodes include a metallic foil.

4. The device of claim 2 wherein sulator means includes a plastic screen.

5. The device of claim 2 wherein sulator means includes a rubber gauze.

6. The device of claim 2 wherein said resilient insulator means includes an electrically non-conductive cloth gauze.

7. A piezoelectric paste transducer system comprising in combination a polarized voltage supply, a transducer adapted to operating as sound transmitter and receiver elements connected to said polarized voltage supply for polarization thereof thereby, said transducer having a thinwalled substantially acoustically transparent sheath, a plurality of flexible electrodes disposed within said sheath, resilient lattice insulator means positioned between said electrodes within said sheath, and a piezoelectric paste distributed within said sheath in contact with the entire inner surface thereof and in contact with the outer surfaces of said electrodes and insulator means.

8. The device of claim 7 wherein said polarized voltage supply includes a series of feed circuits adapted to conduct an input signal and an output signal when said transducer is operating as a sound transmitter ele ment and a sound receiver element, respectively.

9. The device of claim 7 wherein said polarized voltage supply includes a shunt feed circuit adapted to conduct an input signal and an output signal when said transducer is operating as a sound transmitter element and a sound receiver element, respectively.

10. The device of claim 7 wherein said polarized voltage supply includes a direct amplifier feed circuit adapted to conduct an amplified input signal when said transducer is operating as a sound source.

11. A piezoelectric transducer adapted to be operated in a subaqueous medium capable of broadcasting acoustical energy upon excitation by an electrical input signal and producing an electrical output signal upon excitation said resilient insaid resilient inby received acoustical energy comprising in combination a thin-walled, substantially acoustically transparent, leakproof container and a converter unit encased therein, said converter unit having a plurality of electrodes spacially disposed from one another, means for electrically connecting alternate electrodes thereof in parallel, thereby forming a pair of sets of electrodes, one of which is adapted to receive a positive charge and the other of which is adapted to receive a negative charge, a flexible screen insulator means positioned between each of said electrodes, a piezoelectric means distributed within said container in contact with substantially the entire inner surface thereof and among the aforesaid electrodes and insulator means for contact therewith, and insulated electrical lead means passing through said container in such manner that it retains its leakproof characteristics connected to each of said sets of parallel connected electrodes for timely'conducting said electrical output and input signals therefrom and thereto.

12. The device of claim 11 wherein said thin-walled, substantially acoustically transparent, leakproof container is a plastic bag.

13. The device of claim 11 wherein said thin-walled, substantially acoustically transparent, leakproof 'con- 'tainer is a flexible sock having an open end, a header attached to said sock at said open end, and a packing gland mounted on said header for passing said insulated electrical lead means therethrough.

.14. A piezoelectric paste. transducer system comprising in combination a transducer adapted to be operated in a fluid medium and capable of propagating acoustical energy upon excitation by an electrical input signal and producing an electrical output signal upon excitation by received acoustical energy, said transducer including a leakproof container having a flexible sock with an open end, 'a header attached to said sock at said open end, and a packing gland mounted on said header, a converter unit disposed within said container, said converter unit including a plastic end cap and a' mast mounted thereon, a plurality of electrically conductive discs mounted in spaced relationship on and along the longitudinal axis of said mast, means for electrically connectirig alternate discs thereof as two sets of parallel connected discs, one set of which is adapted to receive a positive charge and the other set of which is adapted to receive anegative charge, a resilient lattice insulator positioned along said longitudinal axis between each ofsaid discs, a piezoelectric paste disposed to completely fill that portion of the aforesaid container not occupied by the aforesaid end cap, mast, discs, and insulators, in-

sulatedelectrical lead means passing through said pack- .ing gland in such manner that said container retains its leakproof characteristics connected to each of said "sets of parallel connected discs, and a feed means connected to said electrical lead means for supplying positive and negative charges to said disc sets concomitantly with the conduction of the aforesaid input and output signals.

15. An electroacoustic piezoelectric paste transducer adapted for operation within predetermined subaqueous and atmospheric environmental mediums comprising in combination, a plurality of flexible electrodes, flexible means disposed between said flexible electrodes for insulating same from one another, means surrounding said flexible electrodes and said. flexible insulating means, for containing same as a unitary w-ater tight-air tight package, a piezoelectric paste disposed within said containing means for substantially filling all unoccupied volume therein, and electrical leads respectively connected to' said electrodes for conducting electrical signals there from and thereto. a 1 6. The device of claim 15 disposed in an electrically non-conductivediqu'id.'

8 17. The device of claim 16 wherein said electrically non-conductive liquid includes a silicon fluid.

18. The device of claim 16 wherein said electrically non-conductive liquid includes a transformer oil.

19. The device of claim 16 wherein said electrically non-conductive liquid includes a' castor oil.

20. The device of claim 15 wherein said piezoelectric paste is further characterized as comprising predetermined portionsof finely divided crystals of quartz disposed in an electrically non-conductive fluid.

21. The device of claim 20 wherein said electrically non-conductive fluid includes a silicon oil.

22. The device of claim 20 wherein said electrically non-conductive fluid includes a transformer oil. 7

23. The device of claim 20 wherein said electrically non-conductive fluid includes a castor oil.

24. The device of claim 15 wherein said piezoelectric paste is further characterized as comprising predetermined proportions of finely divided crystals of Rochelle salt disposed in an electrically non-conductive fluid.

25. The device of claim 24 wherein said' electrically non-conductive fluid includes a silicon fluid.

26. The device of claim 24 wherein said electrically non-conductive fluid includes a transformer oil.

27. The device of claim 24 wherein said electrically V non-conductive fluid includes a castor oil.

28. The device of claim 15 wherein said piezoelectric paste in further characterized as comprising predetermined proportions of finely divided granules of barium titanate disposed in an electrically non-conductive fluid.

29. The device of claim 28 wherein said electrically non-conductive fluid includes 'a silicon fluid.

30. The device of claim 28 wherein said electrically non-conductive fluid includes a transformer oil.

31. The device of claim 28 wherein said electrically non-conductive fluid includes a castor oil.

32. An electroacoustic piezoelectric-paste transducer adapted for operation within predetermined subaqueous and environmental mediums comprising in combination,

a plurality of flexible metal electrodes, flexible meansdisposed between said flexible metal electrodes for insulating same from one another, means surrounding said flexible metal electrodes and said flexible insulating means for containingsame as a unitary water tight-air tight package, a polarized piezoelectric paste disposed within said containingmeans' for substantially filling all unoccupied volume therein, said piezoelectric paste includ ing a binder :in such proportions as necessary to provide same with a consistency of predetermined resilience,

for substantially filling all of the unoccupied volume there- V wherein said piezoelectric paste isffurther characterized; as comprisingpredeter imined proportions of finely divided crystals of tourmaline in, a pair of electrical leads appropriately connected to said electrodes for transmitting electrical signals therefrom and thereto, a series connected battery. and inductance interconnectingsaid pair of electrical leads, and I a coupling capacitor connected to one of said pair of electrical leads.

34. A piezoelectric paste'transducer system comprising in combination, a plurality of spatially disposed electri- 'cally conductive metal foil electrodes, flexible plastic lat-' tice means placed'between said electrodes for insulating same from one another, resilient rubber case means sur-;

rounding said electrodes and said insulating means for i containing same as a unitary package, a piezoelectric paste disposed within said containing means for filling substantially all unoccupied volume therein, said piezoelectric paste consisting of a plurality of finely divided crystals of barium meta titanate combined with an electrically nonconductive silicon fluid in such proportions as to form a mixture having a predetermined paste consistency, electrical leads appropriately connected to said electrodes for transmitting electrical signals therefrom and thereto, and means consisting of a series connected battery and inductance interconnecting said pair of electrical leads l9 and a coupling capacitor connected to one of said pair of electrical leads for sup-plying a polarizing voltage to said piezoelectric paste.

35. The invention according to claim 34 wherein said piezoelectric paste disposed Within said containing means for filling substantially all unoccupied volume therein is further characterized by incorporation of a plastic binder that is mixed with said crystals of barium meta titanate and the aforesaid non-conducting silicon fluid.

No references cited.

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