US3382841A

US3382841A - Flexural disc transducer

Info

Publication number: US3382841A
Application number: US396168A
Authority: US
Inventors: John V Bouyoucos
Original assignee: General Dynamics Corp
Current assignee: Hydroacoustics Inc
Priority date: 1964-09-14
Filing date: 1964-09-14
Publication date: 1968-05-14
Anticipated expiration: 1985-05-14

Description

FLEXURAL DISC TRANSDUCER Filed Sept. 14. 1964 64 INVENTOR. 6 JOHN M BOUYOUCOS 56 571 573 584 W259 MHW F/g. 5 584 AGE/VT United States Patent O f 3,382,841 FLEXURAL DISC TRANSDUCER John V. Bouyoucos, Rochester, N.Y., assignor to General Dynamics Corporation, a corporation of Delaware Filed Sept. 14, 1964, Ser. No. 396,168 7 Claims. (Cl. 116-137) This invention relates to transducers for the generation and radiation of acoustic energy, and particularly to a flexural disc transducer. In a flexural disc transducer, the member which radiates acoustic energy is a disc or plate which exhibits an elastic, flexural mode of vibration rather than a rigid body piston-like motion.

Although the present invention is suited for more general applications, it is particularly adapted for use in deep underwater sound generators, as in the hydroacoustic transducers described in an application for a US. Letters Patent, Ser. No. 151,516 entitled, ElectrmHydroacoustic Transducer, and filed by John V. Bouyoucos on Nov. 10, 1961 now U.S. Patent 3,212,473 and in U.S. Letters Patent No. 3,004,512 entitled, Acoustic-Vibration Generator and Valve, issued Oct. 17, 1961, to John Bouyoucos.

There exists a need for underwater sound generators which can withstand high hydrostatic pressure and deliver high acoustic power into the surrounding water. In the above-mentioned US. patent application for Electro- Hydroacoustic Transducers, there as described various hydroacoustic transducers wherein a radiating element constitutes a piston which moves as a rigid body connected to an elastic support which acts as a spring. While such transducers have the advantage of presenting a uniform velocity distribution across a face of the radiating element, they often are comparatively heavy because of the amount of solid material necessary to provide adequate piston rigidity.

Patent No. 3,004,512 describes a thin spherical shaped Wall member that vibrates in response to fluid pressure variations in the acoustic generator. This wall member is adapted for transmitting or coupling acoustic energy into a surrounding body of water.

Bender plate or flexural disc transducers using piezoelectric materials are known. However these transducers generally have limited power handling capability owing to the stress limitation of the ceramic used therein, or have limited depth capability due to stress limitations in the plate or disc supporting member.

It is accordingly an object of the present invention to provide an improved sound generator having a flexural disc radiating element that transmits high acoustic power to a surrounding fluid medium and is light in weight and not subject to harmful stress levels.

It is another object of the present invention to provide an acoustic vibration generator which is adapted either to radiate acoustic energy uniformly at relatively high energy density from a large surface area or to couple to a load acoustic energy having high energy density.

Another object of the present invention is to provide an acoustic vibration generator having a relatively light coupling member which provides for eflicient power transfer between a sound generator and a load.

It is a more specific object of the present invention to provide a transducer which can sustain high hydrostatic pressure and still handle high acoustic power.

It is another object of the present invention to provide a transducer having a large power handling capability without the need for sliding fluid seals.

It is still another object of the present invention to provide an improved edge support for acoustic coupling members.

It is yet another object of the present invention to 3,382,841 Patented May 14, 1968 provide apparatus for decoupling an acoustic radiating element from its supporting structure.

Briefly described, a sound generator embodying the invention makes use of an improved flexural disc radiating element which provides large acoustic power handling capability without the aforesaid disadvantage of piston or thin spherical shaped wall members. This flexural disc radiating element also provides an acoustic transformer for transferring acoustic energy from a relatively small cross-sectional area to a relatively large cross-sectional area so that the impedances of an acoustic energy source and a load can be matched to each other.

The flexural disc radiating element in a preferred embodiment of this invention includes a unitary or monolithic structure having a flexural disc radiating portion, a peripheral mounting portion, and a thin shell or hollow, column-like structure connected between the radiating portion and the peripheral mounting portion. The flexural disc radiating element has two annular coaxial grooves located near the peripheral mounting portion of the disc, which grooves, in cooperation with the thin shell, separate and isolate the radiating portion from the peripheral mounting portion.

The two coaxial grooves are formed partway into the flexural disc radiating element from opposite sides and at different radii in a side by side relationship, so as to define the thin shell or hollow column-like structure between the radiating portion and the peripheral mounting portion. One end of the thin shell is fixed and integral with the peripheral mounting portion, while the other end of the shell is fixed and integral with the radiating portion. The thin shell is relatively flexible for lateral forces or movement at the ends thereof, but is substantially rigid for end thrust or longitudinal forces. The thin shell resists and is stiff to piston-like movement of the radiating portion, but is compliant to flexing or bending movement at the edge of the radiating portion. Thus, the radiating portion can be forced into a highly desirable edge-supported flexural mode of vibration for coupling acoustic energy from the generator to a surrounding fluid medium.

The monolithic structure eliminates the need for sliding hydrostatic seals. The flexural disc may be centerdriven or driven in a distributed manner by various means such as a hydroacoustic or electroacoustic force generator. One advantage of the invention is that a centerdriven all metallic flexural disc radiating element is simple in design and construction and presents an extremely rugged interface to the external environment. Another advantage resides in the fact that two flexural disc radiating elements may easily be mounted in a back to back relationship to provide a double end radiating element. A further advantage resides in the fact that the flexural disc radiating element may be flooded with a compliant liquid. In the latter case, the resonant frequency of the transducer is determined by the combined stiffness of the radiating portion and its backing fluid and the total effective mass of the moving system. Since a compliant liquid backed transducer is readily pressure equalized to ambient pressure, such as .a transducer is suited for deep submergence application.

The invention itself, both as to its organization and method of operation, as well as additional objectives and advantages thereof, will become more readily apparent from a reading of the following description in connection with the accompanying drawing in which:

FIG. 1 is a cross-sectional view, along a vertical central plane, of a flexural disc transducer in accordance with the invention;

FIG. 2 is a perspective view of another flexural disc transducer also embodying the invention, the transducer having a flexural disc radiating element;

FIG. 3 is an elevational view, partially in section of the transducer shown in FIG. 2;

FIG. 4 is a sectional view, taken along a diametral plane, of the flexural disc radiating element shown in FIG. 2 in a rest or neutral position;

FIG. 4a is a view similar to FIG. 4, of the flexural disc radiating element in an exaggerated position during a fiexural mode of operation; and

FIG. is a sectional view, taken along a diametral plane, of a flexural disc transducer employing electrostrictive ceramic elements for driving the flexural disc radiating element thereof in accordance with another embodiment of the invention.

FIG. 1 illustrates a hydroacoustic transducer 10 of the type described in U.S. patent application, Ser. No. 151,516 mentioned above, which includes a flexural disc radiating element 12 secured to one end of a stationary housing 13. Flexural disc radiating element 12 includes a drive piston 14. Drive piston 14 is contiguous to a drive cavity 18 of the housing 13 and moves axially in a cylindrical bore 15 in consequence of acoustic pressure signals generated within

drive cavities

18 and 19. These pressure signals are developed by a modulation of the flow of a hydraulic fluid through a variable area orifice 20 defined by a metering rim 22 of a movable valve 23 and the corresponding rim 24 of an inwardly extending pontion 25 of a stationary port structure 26. The hydraulic fluid enters under pressure at an inlet port 27 and passes through an inlet line 28 and through line branches 29 and 30 into

drive cavities

18 and 19. The direction of fluid flow is indicated in the various figures of the drawing by arrows.

The branches 29 and 30 of FIG. I combine to form a loop 32 which provides an inertance in parallel with the acoustic compliance of

cavities

18 and 19. The fluid passes from cavity 18 through orifice 20 and thence at reduced pressure into discharge chamber 34 which communicates, through an outlet line 35, with a fluid exit port 36. The valve 23 is driven in a direction axially thereof along a path past the stationary port structure 26. An electromechanical force generator 38 drives the valve 23. The generator 38 includes a moving coil 39 free to move in magnetic field structure gap 40 when energized by an electrical control input signal supplied to the coil 39 by way of a pair of leads 42. The coil 39 is wound upon a portion of a spider 44 and the movement of the coil 39 is communicated to the valve 23 through a connecting rod 45. If the resonant frequency defined by the mass of the moving system and the stitfness of the spider is placed above the operating frequency range, the valve displacement will be directly proportional to and in phase with the input signal. In moving in reciprocal fashion within the port structure 26, the valve 23 cyclically varies the size of the orifice 20. A variational velocity disturbance or change in the velocity of the fluid generated by the size change at orifice 20 can give rise either to compression or expansion of the fluid within

drive cavities

18 and 19 or to motion of the fluid within loop 32. The combination of

cavities

18 and 19 and the loop 32 thus constitutes an acoustic tank circuit.

As the pressure variations in the cavity 19 are 180 out of phase with the pressure variations in the cavity 18 at the nominal operating frequency, a point of zero pressure variation (acoustic ground) is found along the inertance loop 32. This point is used as the feed-in point for hydraulic fluid, thereby reducing the possibility of coupling energy from the acoustic tank circuit of the transducer back into the unidirectional flow source. Thus the line 28 terminates at the zero pressure point. The cavity 19, as shown in FIG. 1, is larger than the cavity 18; consequently, the zero pressure point along inertance loop 32 will be nearer the larger cavity 19. It should be understood that the

drive cavities

18 and 19 may be of the same size in certain applications. Because of the presence of the inertance presented by a loop 32, it

is possible to tune and resonate, independently of each other, the acoustic tank circuit and the load coupling circuit. The load coupling circuit is made up principally of the effective mass of the fiexural disc 12 and the flexural compliance of the disc 12 associated therewith. The injection of fluid from orifice 20 into the parallel tank circuit result in pressure variations therein which, in turn, operate on the surface of the drive piston 14 to gener ate motion of the flexural disc radiating element 12 against an external load, such as a body of water.

The fiexural disc radiating element 12 is made from a high strength elastic material such as aluminum alloy 7G75-T6 having a composition of 5.5% Zn, 2.5% Mg, 1.5% Cu and 0.3% Cr. The flexural disc radiating element is driven by a piston 14 which may be an integral part of the fleXural disc radiating element 12 or may be driven by various other ways as illustrated in FIGS. 3 and 5 and described hereinafter. The flexural disc radiating element 12 (FIG. 1) comprises a radiating portion 68 which includes the piston 14, a peripheral mounting portion 61 and a hollow column-like portion which is in the shape of a thin cylindrical shell 62. This shell 62 is defined by two coaxial

circular grooves

65 and 66 lo cated near the peripheral mounting portion 61 of the flexural disc radiating element 12. The

coaxial grooves

65 and 66 are blind, i.e. they extend only part way into the fiexural disc radiating element 12 and from opposing sides. The grooves have different diameters; i.e., they are at different radii from the center of the disc. The grooves are in side-by-side relationship so as to define the thin cylindrical shell 62. The thin shell 62 is connected to the radiating portion 60 at one end 63 and to the peripheral mounting portion 61 at the other end 64 of the thin shell 62 The thin shell 62 provides an improved cylindrical edge support for the radiating portion 60. The wall of the thin cylindrical shell 62 is substantially perpendicular to a radiating face 67 of the radiating portion 60; i.e., the axis of the shell 62 is perpendicular to the face 67. The thin shell 62 behaves in accordance to the physical laws governing thin cylindrical shells when subjected to end thrust and lateral forces applied to the

ends

63 and 64; that is, the thin shell 62 is stiff and highly resistive to end thrust or to piston-like movement of the radiating portion 60. The thin shell 62 however is free to bend in response to lateral forces exerted at its

ends

63 and 64. The thin shell 62 is particularly compliant to lateral forces generated at the end 63 when the radiating portion 60 .is vibrated in a flexural mode.

The radiating portion 60 has a disc-like body similar to the radiating portion 160 shown in perspective view in FIG. 2. The radiating portion 60 has a diameter to thickness ratio which may be in the order of approximately 8:1. A fiexural radiating disc element 12 has been built and operated with a radiating portion 60 having a diameter of approximately 17.5 inches and a thickness of approximately 2 inches. The dimensions just given are for illustrative purposes only.

The peripheral mounting portion 61 is securely clamped to the housing 13 by bolts 54. The peripheral mounting portion is shown as ring-like in cross sectional area. However, the mounting portion 61 may have other shapes. An O-ring provides a seal between the flexur-al disc radiating element 12 and the housing 13. The peripheral mounting portion 61 includes a series of mounting holes 67 for the bolts 54. The mounting holes 67 are uni formly spaced so as to provide an even clamping between the mounting portion 61 and the housing 13.

When vibratory fluid forces are applied on the face 59 of drive piston 14, the radiating portion flexes in a fiexural mode of vibration as though that portion were supported along its circular edge. The radiating portion 60 is forced into this flexural mode of vibration, since the edge support provided by the thin shell 62 is stiff to ex tension and compression and therefore offers :a high impedance to piston-like movement of the radiating portion 60 or to axial translation of the edge of radiating portion 60. The thin shell 62, however, ofiers comparatively negligible impedance to bending or to lateral movement of the edge of radiating portion 60. Freedom for bending yet high impedance to piston action or axial translation provided by the

ends

63 and 64 and by the thin shell 62 respectively, enables the flexural disc radiating element 12 to exhibit an edge-supported flexural mode of vibration rather than a piston-like mode of virbation. 'Dhis edge-supported mode of vibration is characterized by an axial displacement of the radiating portion 60, which starts at the end 63 of the thin shell 62 and reaches a maximum at the center of the radiating portion 60. The manner in which the radiating portion 60 and the thin shell 62 bends or flexes is shown in more detail in another embodiment of the flexural disc radiating element in FIGS. 4 and 4a, and will be described more in detail hereinafter.

In FIGS. 2 and 3 there is shown a single embodiment of a modification of the device of FIG. 1. Elements of the device of FIGS. 2 and 3 corresponding to those of FIG. 1 are indicated by the same reference numeral plus 100. The device of FIGS. 2 and 3 aside from certain mechanical assembly details differ essentially in that the flexural disc radiating element 112 is backed with a compliant liquid instead of air. The drive piston 114 is shown as a free piston which is biased against the radiating portion 160 by a pressurized fluid in the chamber 118. The drive piston 114 includes an O-ring 153.

The transduced 110 of FIGS. 2 and 3 is particularly useful for transducers which are submerged to a considerable depth in sea water. The pressure of the backing liquid within cavity 152 may be equalized to the pressure of the sea in which the transducer 110 is submerged by means including a rubber diaphragm 77 trapped between two anchor members 70 and 7-1 of an assembly 73 and attached by screws 74 to the portion 80 of the housing 113. The rubber diaphragm 77 is exposed on one side to ambient sea water passing through a perforated cover 76 Which also forms a portion of the assembly 73. The rubber diaphragm 77 is also exposed to the fluid in the interior of the cavity 152 by means of a narrow passage 85 in the portion 80 of the housing 113.

The flexural disc radiating element 112 is attached to the periphery of the portion 80 of the housing 113 by bolts 154.

The transducer 110 also includes a hydraulic input port assembly 91 and an output port assembly 92, which include

flanges

93 and 94 connected to :a portion 95 of the housing 113 by bolts 96. The portion 95 of the housing 113 is bolted to the enlarged housing portion 80 by .bolts 97. Acoustic pressure variations produced Within cavity 118 of the hydroacoustic amplifier 110 produces vibratory hydraulic forces on the drive piston 114 which causes movement of the flexural dis-c radiating element 112 in a manner similar to that shown and described in FIG. 1, except, of course, the piston 114, while biased to remain in contact with radiating portion 160, is not an integral part of the radiating portion 160. The fluid within cavity 152 is isolated from the acoustic amplifier drive cavity 118 by means of the O-ring 153 cooperating with drive piston 114. Similarly, fluid leakage from cavities 118 and 152 to the exterior of housing 113 is prevented respectively by O-

rings

98 and 155.

In the operation of the device shown in FIGS. 2-4a inclusive, the hydroacoustic amplifier 110 produces acoustic pressure variations in the cavity 118 in a similar way as described for the device of FIG. 1. The average pressure in the cavity 118 biases the free piston 114 against the radiating portion 160 with sufiicient force so that piston 114 will remain in intimate contact with radiating portion 160 throughout the cycle of vibration. The alternating pressure variations in the cavity 118 are transmitted thru the free piston 114 to the radiating portion 160. The free piston 114 exerts :a dynamic force on the radiating portion 160, which force is equal to the product of the alternating pressure variations in cavity 118 and the cross-sectional area of piston 114.

The radiating portion 160 is shown in FIG. 4 in a neutral or rest position. Shown at 99 are a plurality of uniformly distributed force arrows representing a uniform load such as the hydrostatic ambient sea pressure acting on a front face 158 of the radiating portion 160, when the back face 151 is, for example, in contact with air at atmospheric pressure, as might be the case in the structure 0 FIG. 1. The axis of the thin shell 162 and the

grooves

165 and 166 are substantially perpendicular to the front face 158 of the radiating portion 160 so as to withstand high axial forces and yet be relatively compliant to bending moments acting at the end 163, as described previously for the flexural disc radiating element '60 of FIG. 1. The axial forces acting on the thin shell 162 are a summation of all the forces 99 acting normal to the face 158.

The static axial stress in the thin shell 1-62 is equal approximately to the net axial static force exerted on radiating portion 160 divided by the cross-sectional area of the thin shell 162, as established by its diameter and wall thickness. Once the axial force has been specified, as for example, by specifying the maximum depth of operation, a cross-sectional area of the thin shell 162 can be selected to achieve a satisfactory stress level. The bending moment exerted by the thin shell 162 on the edge of radiating portion 160, as well as the bending stress in thin shell 162, can then be controlled by the choice of the length of the thin shell 162. The ability to choose independently the shell thickness to contral axial stress, and the shell length to control bending stiffness and bending stress is a particularly attractive and important feature.

When the hydroacoustic amplifier is operated, the drive piston 114 is responsive to the alternating pressure in the cavity 118 and drives the radiating portion 166 into a flexural mode of vibration as previously described for. the radiating portion 60 of FIG. 1. FIG. 4a shows the radiating portion in an exaggerated flexural deflection to show the displacement of the radiating portion 160 across its faces 158 and 159 and to show at the same time the displacement of the thin shell 162. The radiating portion 160 flexes about its neutral axis While the thin shell 162 flexes in a cylindrical plane which is substantially perpendicular to the neutral axis of the radiating portion 160. Effectively, it appearsthat the radiating portion 160 flexes substantially about .its neutral axis along a line substantially midway between the

ends

163 and 164 of the thin shell 162.

FIG. 5 shows a flexural disc radiating element and electroacoustic drive means for driving the fiexual disc radiating element into a flexural mode of vibration. Elements of the flexural disc radiating element of FIG. 5 corresponding to those of FIG. 1 are indicated by the same reference numeral plus 500. The flexural disc radiating element 512 comprises a radiating portion 560, a peripheral mounting portion 561, and a thin shell 562. The peripheral mounting portion 561 is substantially similar to the mounting portion 161 of the flexural disc radiating element 112 of FIG. 3. Mounting holes are provided at 554. The thin shell 562 is encircled by two

proximal grooves

565 and 566.

The radiating portion 560 includes two

cavities

570 and 571 on

faces

558 and 559 respectively. Disposed in the

cavities

570 and 571 are piezoelectric members, such as electrostrictive

ceramic discs

572 and 573 respectively. The

discs

572 and 573 are loaded tightly within the

cavities

570 and 571 so that any radial expansion or contraction of the elec-trostrictive

ceramic discs

572 and 573 will be translated into flexural motion of the radiating portion 560. Electrostrictive ceramic disc 572 includes

flat electrodes

578 and 579 connected to input

terminals

580 and 581 respectively. Electrostrictive ceramic disc 72 is polarized so as to expand and contract in a radial direction in response to a varying AC signal applied to input terminals 586 and 581.

Electrostrictive ceramic disc 573 includes electrodes 583 vand 584 connected to terminals 535 and 586 respectively. Electrostrictive ceramic disc 573 is also polarized to expand and contract in a radial direction, in response to a varying AC signal applied to the input terminals 585 and 586.

In the operation of the device of FIG. 5, and AC electrical input signal is applied to input

terminals

580 and 581 of the electrostrictive ceramic disc 572 and to input terminals 584 and 535 of electrostrictive ceramic disc 573 in a manner well known to those skilled in the art so that electrostrictive ceramic disc 572 Will expand and contract while electrostrictive ceramic disc 573 will contract and expand alternately during each cycle of the AC electrical signal. In response to the phase opposed radial expansion and contraction of electrostrictive

ceramic discs

572 and 573 respectively, the radiating portion 560 is urged into a flexural mode of vibration. The frequency of the vibrations is a function of the frequency of the electrical input signal applied across electrostrictive

ceramic discs

572 and 573.

The device of FIG. 5 is particularly advantageous over prior art devices since the flexural disc radiating element 512 incorporates an edge support for the electrostrictive

ceramic discs

572 and 573 which may be exceptionally stiff for axial translation of the edge, yet which provides a low bending moment for the radiating portion 560 at its edge. The low stress inherent in the design of the peripheral mounting portion 561 enables the electrostrictive discs such as 572 and 573 to be used for transducers which are subjected to high hydrostatic pressures.

Whereas the above examples have illustrated the use of hydroacoustic and electrostrictive means as force generators to drive the flexural disc radiating element of the invention, other force generators are equally applicable, such as moving coil, magnetostrictive, and purely mechanical generators. Accordingly, the foregoing description should be taken as illustrative and not in any limiting sense.

What is claimed is:

1. A transducer comprising (a) a disc radiating element of elastic material having a peripheral mounting portion and a disc-like radiating portion,

(b) said disc radiating element including coaxial grooves on opposite faces thereof encircling said radiating portion to define a thin cylindrical shell therebetween connected,

(c) said thin cylindrical shell providing at one end thereof a lateral compliant edge support for said one edge of said radiating portion, and

(d) means coupled to said radiating portion to excite said radiating portion into vibration.

2. An acoustic vibration transducer comprising (a) a flexural disc radiating element having a peripheral mounting portion and a disc-like radiating portion,

(b) said disc-like radiating portion having two substantially parallel edges,

(c) said flexural disc radiating element including relatively deep proximal coaxial grooves on opposing faces thereof encircling said radiating portion to define a thin cylindrical shell therebetween, said shell having an axis substantially normal to at least one surface of said radiating portion,

((1) said thin cylindrical shell providing at one end thereof an edge support for said one of said edges of said radiating portion,

(e) said shell having less impedance to lateral forces than to longitudinal forces applied at said one edge, and

(f) means coupled to said radiating portion to excite said radiating portion into vibrations.

3. An acoustic vibration transducer comprising (a) a disc-like radiating element of elastic material having a peripheral mounting portion and a disc-like radiating portion,

(b) means coupling the outer periphery of said mounting portion for providing less impedance to a force in a direction along the surface of said disc than to a force transverse to said surface, and

(c) means coupled to said radiating portion to excite said radiating portion into vibrations.

4. An acoustic vibration transducer comprising (a) a flexural disc radiating element having a peripheral mounting portion and a disc-like radiating portion,

(b) said flexural disc element including relatively deep proximal coaxial grooves on opposing faces thereof in a side by side relationship to define a thin short cylindrical shell substantially normal to said radiating portion,

(c) said shell being connected at one end to said peripheral mounting portion and at the other end to one edge around one face of said radiating portion,

(d) said thin cylindrical shell providing a circular edge support for said radiating portion having less impedance to flexing of said radiating portion than to piston-like movement of said radiating portion, and

(e) means coupled to said radiating portion for exciting said radiating portion into vibrations.

5. An acoustic vibration transducer comprising (a) a housing including annular support means, at least a portion of said housing defining a path for the steady flow therethrough of a fluid medium under pressure,

(b) fluid chamber means,

(c) fluid flow switching means including a movable valve interposed in said path for modulating repetitively the flow of fluid through said chamber means, the movement of said valve converting a portion of the steady flow energy into acoustic vibrations within said chamber means,

(d) a drive member set in motion in response to said acoustic vibrations,

(e) a flexural disc radiating element having a peripheral portion rigidly secured to said support means,

(f) said disc element also including a radiating portion and a thin cylindrical shell portion integral with said disc,

(g) said thin shell portion being connected to said peripheral portion at one end thereof and being connected to said radiating portion at the other end thereof,

(h) said drive member operatively engaging said radiating portion of said disc, and

(i) said radiating portion being set into vibration in consequence of the motion of said drive member.

6. An acoustic vibration transducer comprising (a) a housing including annular support means, at least a portion of said housing defining a path for the steady flow therethrough of a fluid medium under pressure,

(b) fluid chamber means,

(6) fluid flow switching means including a movable valve interposed in said path for modulating repetitively the how of fluid through said chamber means,

(d) the movement of said valve converting a portion of the steady flow energy into acoustic vibrations Within said chamber means,

(e) a drive element driven in response to said acoustic vibrations,

(f) a flexural disc radiating element having a peripheral portion rigidly secured to said support means,

(g) said disc further including a radiating portion and a thin cylindrical shell integral with said disc element,

(h) said radiating portion and said thin cylindrical shell being disposed within said peripheral portion of said fiexural disc radiating element and formed by closely spaced oppositely directed coaxial grooves within said disc element,

(i) said grooves being disposed along different radii on said disc element,

(j) said drive element operatively engaging said radiating portion of said disc element, and

(k) the diameter of said radiating portion being long compared to the thickness dimensions of said radiating portion.

7. A transducer comprising (a) a flexural radiating element having peripheral mounting portions and a radiating portion,

(b) said flexural radiating element including spaced apart grooves on opposite faces thereof encompassing at ieast a part of said radiating portion to define thin columns interconnecting said radiating portion to said peripheral mounting portions,

(c) said thin columns providing at one end thereof an edge support for said radiating portion, and

(d) means coupled to said radiating portion to excite said radiating portion into vibrations.

References Cited UNITED STATES PATENTS LOUIS J. CAPOZI, Primary Examiner.

Claims

1. A TRANSDUCER COMPRISING (A) A DISC RADIATING ELEMENT OF ELASTIC MATERIAL HAVING A PERIPHERAL MOUNTING PORTION AND A DISC-LIKE RADIATING PORTION, (B) SAID DISC RADIATING ELEMENT INCLUDING COAXIAL GROOVES ON OPPOSITE FACES THEREOF ENCIRCLING SAID RADIATING PORTION TO DEFINE A THIN CYLINDRICAL SHELL THEREBETWEEN CONNECTED, (C) SAID THIN CYLINDRICAL SHELL PROVIDING AT ONE END THEREOF A LATERAL COMPLIANT EDGE SUPPORT FOR SAID ONE EDGE OF SAID RADIATING PORTION, AND (D) MEANS COUPLED TO SAID RADIATING PORTION TO EXCITE SAID RADIATING PORTION INTO VIBRATION.