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Publication numberUS3277433 A
Publication typeGrant
Publication dateOct 4, 1966
Filing dateOct 17, 1963
Priority dateOct 17, 1963
Publication numberUS 3277433 A, US 3277433A, US-A-3277433, US3277433 A, US3277433A
InventorsToulis William J
Original AssigneeToulis William J
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Flexural-extensional electromechanical transducer
US 3277433 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

ct. 4, 1966 w. J. ToULls 3,277,433


W/LL /M J. TOUL/S C' 4, 1966 w. J. ToULls 3,277,433

FLEXURAL-EXTENSIONAL ELECTROMECHANICAL TRANSDUCER Filed 001;. 1.7, 1963 5 Sheeis-Sheet 3 INVENTOR. W/LL /A M J. TOULS d www ATTO/VEYS 3,277,433 FlLEXlURAlJ-EXTENSHQNAL ELECTRO- MECHANICAL TRANSDUCER William ll. Toulis, 1100 E. Broad St., Columbus, Ohio Filed (9ct. 17, 1963, Ser. No. 317,097 3 Claims. (Cl. 340-8) 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 relatesV to an electromechanical transducer adapted to detect or generate and radiate sound in fluid media and more particularly to such a transducer having a diaphragm which operates in the flexural mode of vibration, a driver (for vibrating said diaphragm) which operates in the extensional mode of vibration, and in which the diaphragm and driver are linked together thr-ough a mechanical transformer, in order to couple more efficiently the vibrational energy transfer between the driver and the diaphragm.

Among Objects of importance of the present invention are:

To provide preferably a very-nearly-omnidirectional electroacoustic transducer.

To provide .a transducer having low vibrational mass for broad frequency response.

To provide a transducer which may have high electromechanical conversion eiciency so that the radiated power may be large over a broad band of frequencies.

To provide a transducer employing a piezoelectric ceramic driver where the power output is not limited by th-e tensile strength of the ceramic material of which the driver is composed.

To provide a composite transducer comprising a given number of individual diaphragm-driver sections whose cooperative action gives the transducer an improved frequency response and power output.

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 drawing in which:

FIG. 1 is the transducer assembly, shown partly in section;

FIG. 2 is an exploded view of the transducer seen in FIG. 1 to show with greater clarity the majority of the various components which go into the assembled transducer;

FIG. 3A shows one of the identical diaphragm-driver sections (of the transducer) utilizing a (slightly modified) compliant tube shape structure for the diaphragm (ie, radiating surface);

FIG. 3B shows a like diaphragm-driver section with a modified (honeycombed) diaphragm;

FIG. 3C shows a like diaphragm-driver section with another modification of the diaphragm (i.e., a mass loaded diaphragm); and

FlG. 3D shows a transducer section reflecting the use of a standard compliant tube shape diaphragm and spacer, in contradistinction to the FIGS. 3A-3C which show a transducer section wherein the compliant tube form has been slightly modified to enable it to be used as a radiating surface (diaphragm) without the need for spacers FlG. 4 shows in perspective details of one transducer section embodying this invention.

The principal portion of the transducer 11 is a series of substantially-identically constructed sections 12. FIG. 3(A-D) portrays a preferred embodiment of one of these sections 12. Each of these sections 12 consists essen- Patented Oct. 4, 1966 tially of a diaphragm 13 which is adapted to undergo flexural vibration to transmit sound into the fluid medium in which the transducer is immersed and a driver 14. The driver 14, mounted in thrust-transmitting relationship with diaphragm 13, is adapted to operate in the longitudinal (extensional) mode of vibration to impart to its diaphragm 13 the desired flexural vibrational motions.

The diaphragm 13 is essentially a section of compliant tubing, a structure which is defined at length in the inventors issued Patent No. 3,087,138, and in the inventors issued Patent No. 3,021,504. Aluminum is a representative material for this diaphragm 13. In the preferred embodiment shown here an elliptically-shaped compliant tube, of aluminum or like material, is employed for the diaphragm. The diaphragm may be solid in structure (FIG. 3A) or it may be honeycombed (i.e., made longitudinally perforate) as seen in FIG. 3B, the latter structure serving to produce a diaphragm of reduced density. The perforations 16 (shown in the FIG. 3B diaphragm embodiment) may extend throughout the longitudinal length of this diaphragm 13. The density of the diaphragm 13 may also be increased (rather than decreased) by the addition to the normal solid diaphragm (unperforated) of an additional loading charge. A mass loaded diaphragm is shown in the FIG. 3C diaphragm embodiment where lead bars 17 are fixedly secured to the inner surface of the diaphragm at both sides there-of as shown. These lead bars 17 are preferably mounted in opposing center balancing positions at opposite sides of the diaphragm 13, with their respective longitudinally-running center lines lying along the plane of symmetry defined by the various minor axes of multiple cross sections of the diaphragm 13 and preferably these bars 17 run the full longitudinal length of the diaphragm 13. The variations of the diaphragm 13, as just described, are utilized as methods for varying the mechanical Q of the transducer 11 which is composed of these sections 12. The mechanical Q of a transducer increases with the density, the thickness, mass loading, degree of curvature or stiffness of its diaphragm. This mechanical Q or sharpness of resonance of a vibrating structure is highly significant in terms of the electrical efficiency, acoustic power output and effective frequency bandwidth. A high mechanical Q leads to high efficiency and power output, but at a sacrifice in usable bandwidth. A low mechanical Q, on the other hand, improves usable bandwidth at the expense of efliciency and power output. Use of a honeycomb structure diaphragm (FIG. 3B) conveys the advantages of a low mechanical Q (improved frequency response). On the other hand, mass loading of the diaphragm (FIG. 3C) such as with lead bars 17 improves the efficiency and power output of the transducer, at the sacrifice of usable bandwidth.

The construction of the driver 14 for each of the sections 12 is the same regardless of whether a solid, or honeycombed, or mass loaded diaphragm is employed. The driver 14, as shown, is a ceramic sandwic driver structure which consists principally of a stack of piezoelectric ceramic plates 18. It is well known that certain materials undergo mechanical deformation when various voltages are applied across them. This effect, which can properly be described as the converse of the well-known piezoelectric effect, has been found applicable to various polycrystalline ceramics whose most widely known member is probably barium titanate (BaTiOg), which, when pre-polarized by the application of a sufficiently strong unidirectional field, serves as an excellent transducing element. An illustrative reference on such a barium titanate ceramic is U.S. Patent No. 2,486,560 to Grey. It has been found that, for the application herein, the lead zirconate titanate ceramic 3 (which is disclosed in U.S. Patent No. 2,708,244 to Jaffe) is particularly appropriate.

The maximum power output from a transducer employing a ceramic driver may depend to a large extent on the degree of internal heat dissipation within the piezoceramic, the ability to dissipate heat rapidly and the duty cycle during normal opeartion. When the duty cycle is high and heat dissipation appreciable, the maximum power output (of the transducer) will be limited by the build-up in temperature within the ceramic driver. Because the thermal conductivity of ceramics is low, the piezoelectric ceramic comprising the driver 14 is constructed of thin piezoceramic plates 18 in the configuration of an elongate stack, as seen in the various figures of the drawing. Each of these ceramic plates 18 is plated with silver on two sides first (and preferably on the sides to be bonded) in order to serve as electrodes to polarize and also to drive the stack electrically. These ceramic plates 18 are supplemented by a series of heat-dissipating members 19 each of which consists of two horizontallyextending metallic (i.e. copper) inserts 21 and a vertically-extending fine-wire mesh member 22 which links the metallic inserts 21. With the metallic (preferably copper) inserts 21 sandwiched in-between adjacent ceramic plates 18, heat originating in the ceramic plates 18 on both sides of a metallic insert 21 will be conducted away to the fine-wire mesh member 22 from which this heat will then dissipate.

Heat dissipating members 19 also act as part of the electrical system which actuates the various ceramic plates 18 to cause the driver 14 to vibrate in longitudinal mode in response to the actuating electrical signal. It will be noted, as seen especially in FIGS. 3A-3D that each successive ceramic plate 18 is oppositely polarized from the next preceding ceramic plate. The drawing figures portray, with arrows, the inherent polarization of the various ceramic plates. With the individual heat dissipating members 19 embracing, by their metallic inserts 21, a pair of successive, oppositely-polarized ceramic plates 18, by staggering the heat dissipating members 19 which respectively appear to the left and to the right of the stack of ceramic plates (see FIGS. 3A-D) these heat dissipating members 19 also serve as electricity-conducting electrodes for actuating the ceramic plates 18. Each of the metallic inserts 21 is preferably co-extensive in area with the ceramic plate surfaces between which it is sandwiched so as to present a uniform and mechanically balanced surface to each ceramic plate 18. With heat dissipating members 19 positioned in a staggered series with respect to the stack of ceramic plates 18, there will be formed a vertical row of fine-wire mesh members 22 to the right of the ceramic-plate stack and a like vertical row of fine-wire mesh members 22 to the left of the ceramic-plate stack. A right-hand bus bar 23 is secured in an electrically-conductive connection to the right-hand vertical row of mesh members 22 and a left-hand bus bar 24 is connected in like fashion to the left-hand vertical row of these mesh members 22. With the bus bar 23 connected to the one polarity of the actuating electrical signal and the other bus bar 24 connected to the other polarity of the actuating electrical signal as appropriate for the given polarization of the various ceramic plates 18, the driver 14 (composed of these ceramic plates 18) will vibrate in the longitudinal mode of vibration to impart iiexural vibratile movement to the diaphragm 13.

Located in the stack of ceramic plates 18 which are maintained in rectilinear stack conformation by appropriate conventional bonding are a pair of steel plates 26, each of which is substantially co-extensive with the ceramic plates of the stack. For the majority of sections 12 of transducer 11 each steel plate 26 is equipped at one end with a male prong 27 and at its opposite end with a female opening 28 which is adapted to accommodate a like prong fitted to the steel plate 26 of an adjacent ceramic-plate stack when proximate sections 12 are fitted together to form the assembled transducer (the joining together of the various sections 12 of the transducer 11 will be dwelled upon infra). These steel plates 26 act both as appropriate spacers in the ceramic-plate stack and as a means for securing together various proximally-located drivers 14 of the transducer.

The piezoceramic driver of this invention need not be of the sandwich construction portrayed herein. This piezoceramic driver 14 may be simply an integral, uniform piezo-driver with silver electrodes on appropriate outside surfaces thereof, but preferably it is of the composite sandwich-like construction defined herein, which is considerably more desirable (than the integral, uniform piezo-driver) for attaining maximum output and bandwidth with the transducer. Various other of the novel features of the transducer defined herein can be employed with drivers other than piezoelectric ceramic drivers, such as magnetostrictive drivers, for example.

Located at the respective vertical extrem-ities of the driver stack of ceramic plates are a pair of plastic sheet insulators 29 in compressed position between the vertical ends of the stack of ceramic plates 18 and the adjacent portion of the diaphragm 13 which is formed to accommodate the driver `14 in a tightly-h-olding fit, The conventional compliant tube-shape structure which goes to form the diaphragm 13 may be modified as seen in FIGS. 3A-3C, to form the driver-.abutting portion 31 which contacts plastic sheet insulator 29. On the other hand, if an unmodified elliptically-shaped complaint tube is employed it will be necessary to include, for mechanical reasons, intermediate plastic sheet insulator 29 and the compliant tube 3-2, a spacer 33 (see FIG. 3D). Insulators 29 which are It-o provide electrical insulation between the driver -1'4 and the diaphragm 13 and the spacers 3=3 (when employed) are preferably formed of as stiff a material as possible in order to minimize decoupling between the driver 114 and the diaphragm 13.

One of the limiting factors present when piezoceramic drivers are employed is the propensity for such drivers to fracture when employed for high acoustic power output. "Bhe yield strength of piezoceramics `while in tension has been found to be only in the order of LOCO-4,000 lbs./ ing. The stresses induced by electrical forces in the ceramic are comparable and definitely much higher if the maximum acoustic out-put is to be limited by internal heating. Inasmuch as the compressive strength, however, of piezoceramics is known to be greater than 20,000 lbs/in?, the use of compressive prestress on a piezoceramic driver logically suggested itself as a way to eliminate fracture in the piezoceramic at high power output. The use of biasing stress to prestress the ceramic plates 18 is employed in the transducer 11 so that high acoustic power may be radiated by the transducer without danger of 'fracture of the ceramic. This prestress is mechanically achieved herein simply by forcing inwardly the two vertically extending walls of diaphragm 13 and sliding the ceramic-plate 118 stack, as supplemented by the end insulators 29, into place, as shown, after the proper dimensions and forces are selected to yield the desired degree of (compressional) prestress. When the vertically-extending walls of diaphragm 13 are forced inwardly to enlarge the natural vertical inside-dimension of this diaphragm 13 so that it will be able to accommodate a ceramic driver which is longitudinally-oversized with respect to the natural vertical inside dimension (of the diaphragm) and the positive deforming force removed from the diaphragm 13 .after ythe ceramic driver has been inserted into operative position therewithin, the tendency -of the diaphragm 13 to seek its natural (undeformed) shape is the source of the compressive bias for the ceramic-plate stack. The resulting prestress serves to prevent fracture of the ceramic material of the driver 14. The use of mechanical prestress to improve the yield strength of piezoceramic drivers has been employed previously, as seen for example in the U.S. Patent No. 2,930,912 ent-itled Composite Electromechanical Transducer, and issued to H. B. Miller. In the Miller patent which, like the present invention, employs a stack of ceramic plates in its driver, a plurality of individual stiff rods are used to put and keep under compressive bias the stacked piezoceramic plates of the driver. The mode of effecting this compressive bias (prestressing) herein represents an improvement over that employing a plurality of stilinv rods. In the multiple rod method there is the significant problem of getting equal stress on the ceramic driver 14. A lack of equal stress makes the ceramic liable to buckling and/or chipping. Here the compressive bias placed upon the ceramic driver 14 by diaphragm 13 ensures the application of equal stress thereto. Multiple stiff-rod biasing of the ceramic driver also producesV an incapacitating or degrading factor on the effective electromechanical coupling factor for the transducer because of the stiffness of the rods, that is, it produ-ces a clamping action on the ceramic driver to limit its vibratory motion. Here, on the other hand, the biasing action does not limi-t the vibratile motion of the ceramic driver because the biasing structure (Le. diaphragm) is mechanically resonant at the frequency of operation of the transducer. (The dimensions of the diaphragm 13 herein are such that this diaphragm 13 is equally mass and stiffness controlled at optimum operating frequency, which is generally the resonant frequency. (Stiflness as used here is equatable with elastic resistance t-o change of dimension and mass, as employed here, with inertive resistance to change of motion.)) Another distinction between the presetting bias action here and the multiple rod bias action (such as in the Miller patent) is that in the multiple rod biasing the rods vibrate in the extensional or longitudinal mode of vibration whereas here the compressing (bias) member (diaphragm 13) vibrates in the flexural mode of vibration. This flexural mode of vibration is much more amenable to resonance operation, i.e., driver-compressing diaphragm 13 can be made to resonate with a feasible dimension requirement for the diaphragm. Compressing rods, on the other hand, in order to be able to resonate, would ordinarily be beyond practicable limits in length. The ability of the compressing member to attain resonance enables the transducer to achieve greater power output and efiicieny.

Looking now to the transducer 11 as an assembled unit whose main operative portions are the various sections 12, FIG. l shows the assembled transducer partly in sectional view and FIG. 2 shows in exploded view the various main portions which go to make up the assembled transducer. Proximate transducer sections 12 are mechanically joined together by the union of complementary male and female connection members. The male prongs 27 extending from the steel plates 26 of one of the transducer section 11 are complementarily insertable into mating openings 28 formed in the opposite side of steel plates 26 of the next adjacent transducer section 12, to hold adjoining sections 12 linked together. In like fashion the diap'hragms 13 of adjacent sections 12 are provided with complementary prongs 34 and openings 36 which mate together. Intermediate proximate sections 12 of lthe transducer 11 there is a rubber gasket 37 which serves to develop, in conjunction with the compressive pressure (effected in a manner to be described infra) upon it by each of the proximate sections 12, a liquidproof seal between these proximate sections 12.

The first and last sections 12 of the series of sections 12 which make up the complete transducer diaphragm are variously designated herein as 12 and 12 respectively. The rst section 12 may not have operative need for the openings 28 in its steel plates 2d and the last section 12 may not have prongs 27 (on its steel plates 26) or prongs 34 (on its diaphragm 13). The respective ends of the assembled series of sections 12 are closed off by the respective closure plates 33 and 39, each of which has a rubber gasket 40 inserted between it and the abutting section 12. These closure plates 38 and 39 are appropriately bored to form holes 41 which receive a series of tie-rods 42 which, in conjunction with nuts 43 fastened to their threaded ends, serve both to hold the transducer sections 12 and their intervening gaskets 37 in a tight union and to maintain closure plates 38 and 39 in tight, closing position to seal off the ends of the transducer as well as serving to prevent the closure plates 38 and 39 from shifting laterally with respect to the series of joined transducer sections 12.

One of the closure plates (here shown as closure plate 38) is provided with a liquid-tight electrical coupling member 44 which has two externally located prongs 46 and 47 adapted to link to an external lead 48. The complementary internally-located contact members 49 and 51 of this electrical coupling member 44 are electrically connected to two respective leads S2 and 53. The first of these leads, lead 52, passes from the electrical coupling member 44 to interconnect, in series fashion, each right hand bus bar 23 of the various transducer sections 12 t0 the one polarity-actuated portion of electrical coupling member 44 and the other of these leads, lead 53, acts to electrically link the left-hand bus bars 24 of the respective transducer sections 12 to the other polarity-actuated portion of the electrical coupling member 44. It is in this fashion that the electrical actuating sign-al is carried to the various drivers 14 of each of the sections 12 of the transducer 11. The overall diaphragm of the transducer 11 is comprised of the series of section diaphragms 13 and by way of the extensional vibratory movement of each of the section drivers 14, which all operate in phase with each other, the overall transducer diaphragm is driven in flexural vibratile movement by the actuating signal brought to the transducer 11 by the external electrical lead 48.

Depending upon the depth in the liquid medium at which the transducer 11 is to be employed, the chamber, formed by the closed-off series of sections 12 and containing the series of drivers 14, is either left filled with air or is oil filled or is filled with an appropriate pressurerelease material such as corprene, for example, (practices which are conventional). An appropriate oil is silicone fluid. It must be borne in mind that the oil used must be of a character to prevent electrical arcing between the silver electrodes of the various drivers 14 or between the ceramic plate-s 18 themselves.

The transducer 11, just described, is potentially characterized with high electromechanical efficiency and high power output along with a transmission capacity over a broad range of frequencies. For maximum power output and efficiency it should preferably be operated near mechanical resonance. In its usual dimensions it is very nearly omnidirectional in radiation pattern. The general rule for determining whether a transducer is (selectively) directive, or not, in its radiation pattern is that when the dimensions of the radiating surface of the transducer are small compared to the Wave-length of sound in the enveloping sound-propagating medium, such a transducer does not have directivity, i.e., its radiation pattern is omnidirectional in character. Directivity may be obtained with such transducers, when desired, by arranging multiple such transducers in arrays or employing them in conjunction with acoustic lenses or reectors. The mating of the extensional and exural modes of vibration, as achieved in this transducer, produces a more effective transducer as it yields high acoustic output and desirable electro-acoustic characteristics with a much smaller transducer than has been used previously. In this extensionalexural transducer substantially all of the structure making up the transducer is dynamic For example, in addition to serving as a radiating surface, as a mechanical transformer and as a prestressing agent for the piezoceramic, the diaphragm itself acts as the main portion of the external-liquid-medlum-excluding container with no need for the use of such structure as the conventional rubber boot which often serves as container and which presents the disadvantage of tending to dampen the dynamics of the transducer operation. The simplicity of such a transducer where the diaphragm also serves as the liquid-precluding envelope is patent. As noted supra, the character of the transducer diaphragm can be varied readily to give either increased power output and electroacoustic eiiiciency or greater frequency bandwidth, as desired. With its prestressed ceramic drivers it is able to attain significantly high power output.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is intended to cover all changes and moditications of the embodiments set forth herein which do not constitute departures from the spirit and scope of this invention.

What is claimed is:

l. A composite electromechanical transducer, adapted to transmit or detect sound in a liquid medium, and herein defined in terms of its sound transmission operation comprising in combination:

a plurality of open-ended tubular diaphragm members of identical non-circular cross-sections, each of said tubular diaphragm members being adapted to vibrate in the tiexural mode of vibration for transmitting sound into said liquid medium and said plurality of tubular diaphragm members being arranged in a linear series whereby said diaphragm members form an integrally-operative tubular sound-transmitting means adapted to transmit sound into said liquid medium;

electrically-actuable electromechanical converter means,

individual to and disposed within each of said diaphragm members in thrust-transmitting relationship therewith and vibratile in the longitudinal mode of vibration in response to an actuating uctuating electrical signal, for driving its associated diaphragm member in tiexural vibratile movement in response to said fluctuating electrical signal;

closure means, connected to each end of said tubular sound-transmitting means, for closing off said tubular sound-transmitting means from said liquid medium;

multiple sealing means for ensuring a liquid-proof connection between the adjacent diaphragm members;

electrically-conductive actuating means, connected to each of said electromechanical converter means and adapted to connect to an external electrical lead bearing said iiuctu-ating electrical signs;

restraining means, connected to said closure means, for holding and maintaining said closure means, said plurality of diaphragm members and said sealing means in assembled cooperation relationship with respect to each other;

said converter mean-s each comprising:

a stack of electromechanically-active elements each of which is adapted to alternately expand and contract along the longitudinal axis of said stack in response to the application to said electromechanically-active elements of an electric signal of iiuctuating intensity, the longitudinal ends of said stack being in thrust-transmitting relationship with its associated diaphragm member;

electrode means, operatively interconnecting each of `said electromechanically-active elements to said electrically-conductive actuating means for bringing each of said electromechanically-active elements under the operative influence of the actuating fluctuating electrical signal carried by said electrically-conductive actuating means;

insulator means, intermediate the respective longitudinal ends of said stack of electromechanically-active elements and the diaphragm member associated therewith, for electrically insulating said stack of electromechanically-active elements from said associated diaphragm member; and

heat dissipating means, connected to each of the electromechanically-active elements in said stack for conducting heat away from said electromechanically-active elements, said heat-dissipat ing means, in part, consisting of wire meslrlike structure for accelerating the dissipation of heat away from said electromechanically-active elements.

2. A composite electromechanical transducer comprising in combination:

a plurality of open-ended tubular diaphragm members of identical non-circular cross-section, said diaphragm members being substantially ellipitical in general cross-sectional configuration, each diaphragm member being adapted to vibrate in the tiexural mode of vibration for transmitting sound into water and said plurality of tubular members being arranged in linear series;

electrically-actuable electromechanical converter means individual to and disposed within each of said diaphragm members in thrust transmitting relationship;

each electromechanical converter means being longitudinally elongate and disposed within its associated elliptical tubular diaphragm member with the longitudinal axis of said converter means lying within the plane of symmetry deiined by the major axes of the cross-section of said diaphragm member and with the longitudinal axes of said converter means perpendicular to the plane of symmetry defined by the minor axes ofthe cross-section of said diaphragm member;

said electromechanical converter means each cornprising:

a plurality of electromechanicallyeactive polarizable thin ceramic plates each of which has two oppositely-located substantially-parallel major planar surfaces and each of which is polarized to alternately expand and contract along an axis substantially perpendicular to said major planar surfaces in response to the application thereto of the intiuence of la uctuating electrical signal, the individual ceramic plates of said plurality of ceramic plates being successively stacked on top of one another, with the next-successive ceramic plate in the resulting stack having its major planar surfaces in superimposed position over i the major planar surfaces of the next-precedent ceramic plate to form an elongate stack of said ceramic plates;

insulator means, intermediate the respective longitudinal ends of said elongate stack of ceramic plates and the diaphragm member associated with said electromechanical converter means, for electrically insulating said elongate stack of ceramic plates from its associated diaphragm member;

said stack of ceramic plates as supplemented by said insulator means being of greater length than the natural undeformed inside dimension measured along the major-axis of an elliptical cross-section of said diaphragm member will accommodate, so that placement of said stack of ceramic plates, as supplemented by said insulator means, within its associated diaphragm member necessitates mechanical deformation of the natural cross-sectional shape of said diaphragm member to elongate its cross-sectional majoraxis dimension, said diaphragm member after placement therein of its associated stack of ceramic plates and the insulator means accompanying said stack, imposing a compressive bias upon said stack of cera'mic plates in the direction of its longitudinal axis because of the tendency of said diaphragm member to return to its normal, undistorted cross-sectional shape;

electrode means, operatively connected to each of said ceramic plates which form said elongate stack and also electrically connected to said electrically-conductive actuating means, for conveying to each of said ceramic plates the inuence of said uctuating electrical signal which causes said ceramic plates to alternately expand and contract.

3. The transducer of claim 2 wherein said electromechanical converter means further comprises mesh-like heat dissipating means connected to each of said ceramic 1 plates for conducting heat away from said ceramic plates.

References Cited by the Examiner UNITED STATES PATENTS Hayes 340-9 X Mason 340-8-6 Dranetz.

Barney 340-8 X CHESTER L. JUSTUS, Primary Examiner.

G. M. FlSHER, Assistant Examiner.

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U.S. Classification367/155, 310/337, 367/162, 367/163
International ClassificationB06B1/06, G10K9/00, G10K9/12
Cooperative ClassificationB06B1/0618, G10K9/121
European ClassificationG10K9/12F, B06B1/06C2C