US3516052A - Acoustic apparatus - Google Patents

Description

June 2, 1970 J. v. BOUYOUCOS ACOUSTIC APPARATUS 2 Sheets-sheet 2 Filed Jan. 27, 1965 INVENTOR.

JOHN v. BOUYOUCOS Fig. 4

3,516,052 Patented June 2, 1970 3,516,052 ACOUSTIC APPARATUS John V. Bouyoucos, Rochester, N .Y., assignor to General Dynamics Corporation, a corporation of Delaware Filed Jan. 27, 1965, Ser. No. 428,398 Int. Cl. H04r 23/02; G01v 1/14 US. Cl. 34012 14 Claims ABSTRACT OF THE DISCLOSURE A hydroacoustic amplifier is described having a housing including a path for the flow of pressurized hydraulic fluid through a valving orifice. A lever valve has an end of one of its arms disposed to sweep across the orifice, thereby modulating the flow of hydraulic fluid. The valve is actuated by a hydraulic transformer including a cylinder of electrostrictive material disposed in a hydraulic fluid filled cylindrical cavity. A movable button is disposed between the cylindrical cavity and the opposite end of the valve from the orifice and is actuated in response to variations in pressure in the cavity to operate the lever valve so that it sweeps across the valving orifice. An electric signal applied to the electrostrictive cylinder is translated into hydroacoustic energy which is coupled to a diaphragm for radiation outwardly from the housing.

The present invention relates to acoustic apparatus, and more particularly to hydroacoustic amplifiers by which is meant apparatus of the type which is adapted to control the flow or the particle velocity of a hydraulic fluid under pressure at frequencies Within the acoustic range, which includes the sonic and ultrasonic range.

Hydroacoustic amplifiers are particularly useful for generating low frequency underwater sound, since they can handle high acoustic power at a relatively low frequency while remaining small in size and weight. Among such amplifiers is the hydroacoustic oscillator-amplifier described in US. Pat. No. 3,105,460 issued on Oct. 1, 1963 to John V. Bouyoucos.

Underwater object detection or communication by acoustic means is particularly diflicult to effectuate at long range because of such barriers as attenuation, ambient noise, reverberation, multipath effects, and propagation velocity variations along the transmission path. Attempts in the past to improve acoustic detection or communication means have been to lower the frequency and to increase the size and power of electroacoustic equipment and to provide more complex signal waveforms and concomitant signal processing techniques. Large size electromagnetic, magnetostrictive, or piezoelectric transducers and complex equipment for their control have become necessary. Aside from being more expensive, valuable shipboard space is needed for the complex equipment.

Accordingly, it is an object of the present invention to provide an improved hydroacoustic amplifier for the generation of high energy underwater signals having complex waveforms which are suitable for use in underwater object detection and communication, the improved hydroacoustic amplifier being small in size as compared to conventional equipment for the purpose.

It is another object of the present invention to provide an improved hydroacoustic amplifier which produces high energy underwater signals under control of low energy input signals, which underwater signals are adapted to be in synchronism and in direct phase relation with their controlling input signals.

It is yet another object of the present invention to provide an improved hydroacoustic amplifier which may be controlled so that the amplifier is useful in arrays thereof.

It is still another object of the present invention to provide an improved hydroacoustic amplifier which is particularly useful for underwater detection and communication.

It is another object of the present invention to provide an improved hydroacoustic amplifier capable of operating over a wide frequency range.

It is still another object of the present invention to provide an improved hydroacoustic amplifier capable of generating compressional wave energy which can be frequency and amplitude modulated.

Briefly described, a hydroacoustic amplifier embodying the invention utilizes an electrical control signal applied to a piezoelectric, electrostrictive or similar electromechanical member to produce fluid pressure variations of controlled frequency, amplitude, and phase in a fluid filled cavity. The pressure variations in the cavity are then fluid coupled through a hydraulic transformer to a valving member which controls the modulation of an otherwise steady flow of a fluid medium under pressure through an acoustic chamber. Modulation, in accordance with an embodiment of the invention, is effected by a valving structure including a mechanical transformer (e.g. a lever valve) which is operated by the hydraulic transformer to obtain a large valve stroke from a small movement of the electrical control signal responsive member. Acoustic energy is generated in the chamber as a result of the modulation of the flow of fluid therethrough. The acoustic energy so generated may be coupled out to a load, such as the radiation load of a large body of water, through a suitable coupling structure.

The invention itself both as to its organization and operation as well as additional objects and advantages thereof will become more readily apparent from a reading of the following description in connection with the accompany drawings in which:

FIG. 1 is a rear elevation of hydroacoustic apparatus including a hydroacoustic amplifier embodying the present invention;

FIG. 2 is a cross sectional view of the apparatus of FIG. 1 taken along line 22 of FIG. 1 when looking in the direction of the arrows;

FIG. 3 is an enlarged fragmentary view, in perspective, of a portion of the hydroacoustic amplifier of FIG. 1 showing a valving member and an outlet stator port structure;

FIG. 4 is a sectional view of the hydroacoustic transducer of FIG. 1 taken along line 4-4 of FIG. 1 when viewed in the direction of the arrows, the line 4-4 being perpendicular to the line 22;

FIG. 5 is a fragmentary perspective view of one bearing block which supports the valving member shown in FIGS. 3 and 6;

FIG. 6 is a sectional view of the hydroacoustic amplifier of FIG. 1 taken along line 6-6, which is parallel to line 4-4, looking in the direction of the arrows appended to the line 66, the view showing in more detail the electrostrictive means also shown in FIG. 2; and

FIG. 7 is a schematic diagram of an electrical circuit employed in the hydroacoustic amplifier of FIG. 1.

Referring more particularly to FIGS. 1 and 2, there is shown a hydroacoustic amplifier 10. A valving housing 12 and a chamber housing 13 of the amplifier are connected by bolts 14. An inlet connection 17 is provided in the chamber housing 13 for receiving a low viscosity hydraulic fluid under pressure from an appropriate unidirectional flow source or pump 20 through a main feed line 18. A suitable fluid is hydraulic oil S.A.E. 10. The hydraulic fluid is pumped into an acoustic tank circuit 21 in the chamber housing 13. The acoustic tank circuit includes an acoustic chamber 22 having a given acoustic stiffness reactance and an inertance line 23 having a given acoustic inertive reactance which is substantially equal to the stiffness reactance of the acoustic chamber 22 at the mean operating frequency of the amplifier. By mean operating frequency is meant the center frequency of the range of frequencies over which the amplifier is designed to operate. A receiving chamber 24 is provided between the acoustic tank circuit 21 and the inlet connection 17. The receiving chamber 24 serves to define a pressure release termination or acoustic ground to the inertance line 23. The acoustic tank circuit 21 is similar to the acoustic tank circuit described in the above-referenced US. Pat. No. 3,105,460. The acoustic chamber 22 includes an inlet at 25 and an outlet which is configured to provide a stator port structure 26 for a valving member 31.

The hydraulic fluid enters the acoustic chamber 22 at inlet 25 and passes through the chamber 22 and through the outlet stator port structure 26 to an exhaust chamber 27 in the valve housing 12. The exhaust chamber 27 includes an outlet connection 28 which is connected to a main return line 29. The main return line 29 is connected to an input connection 30 of the pump 20.

The valving member 31 is interposed between the outlet stator port structure 26 and the exhaust chamber 27 and is operative to modulate the flow of fluid through the outlet stator port structure 26 in response to a motivating force, hereinafter to be defined. The valving member 31 is mounted on a shaft 32 which is supported on a pair of bearing support blocks 33 and 34 (FIGS. 4 and The valving member 31 may be adjustable on the shaft 32 and is clamped to the shaft 32 by locking screws 35. The shaft 32 is pinned to the pair of bearing blocks 33 and 34 by pins 36 and 46. The shaft 32 is made of an elastic material such as steel and has reduced sections 37 and 38 which establish a torsion spring suspension for valve member 31. The effective rotary mass of valve member 31 and the torsional spring rate of reduced sections 37 and 38 define a natural or resonant frequency for the combination of the valving member 31 and shaft 32 which resonant frequency is substantially equal to the mean operating frequency the amplifier 10.

The valving member 31 includes at one end 41 a cylindrically curved valving surface 39 which is contiguous to a corresponding cylindrically curved valving surface 40 of the outlet stator port structure 26 (FIG. 3). The valving member 31 also includes a metering edge 42 at its end 41. The metering edge 42 traverses the stator port structure 26 and defines the opening through which the fluid flows. The valving surfaces slide over each other, being separated by a lubricating film of the fluid. The metering edge thus has a wiping action.

The stator port structure 26 includes a rectangular opening 43 which has a length which is just slightly less than the length of the metering edge 42 of the valving member 31. The opening 43 has an edge or rim 48 which, in conjunction with the metering edge 42, defines a variable orifice 49. The valving member 31 is rotatable about the longitudinal axis of the shaft 32 as indicated by the arrows in FIG. 3, to vary the cross-sectional area of the orifice 49.

The valving member 31 includes a lever portion 44 opposite the end 41 for rotating the valving member when the motivating force is applied thereto. The lever portion 44 has at least two oppositely disposed bearing points 70 and 71 which bearing points 70 and 71 may be for example less than one-quarter of the length of the valving member 31 away from the axis of the shaft 32 so that movement magnification at the one end 41 may be achieved. As illustrated in FIG. 3 for example, the distance of the bearing points 70 and 71 of the lever portion 44 from the axis of the shaft 32 is approximately one-quarter of the distance of the one end 41 of the valving member 31 from the axis of the shaft 32, so that a magnification factor of four is achieved.

Thus a small rotary movement of the lever portion 44 results in a magnified movement of the metering edge 42 of the valving member 31 which in turn results in a relatively large change in the orifice area of the orifice 49.

The assembly comprising the shaft 32, the valving member 31 and the supporting blocks 33 and 34 desirably has suflicient stiffness and rigidity to support end thrusts arising from pressure variations in the chamber 22, without undergoing significant deflection or deformation relative to the stator port structure 26.

Referring now to FIGS. 4 and 5 the bearing blocks 33 and 34 are bolted to the chamber housing as by bolts 45 which extend through the holes 45a in the blocks (FIG. 5). The bearing blocks 33 and 34 are of similar construction. Each of the bearing blocks may include a bearing 60 to reduce friction between the block 33 and shaft 32. The bearing blocks 33 and 34 support the valving member 31 as was mentioned previously, so that there is little or no end play of the valving member 31 relative to the outlet stator port structure 26.

The valving member 31 is controllably rotated about the longitudinal axis Of the shaft 32 by an electrostrictive excitation means 50. The electrostrictive excitation means 50 include first and second electrostrictive cylinders 51 and 52, for example of BaTiO coated with conductive material on their inner and outer cylindrical peripheral surfaces, centrally disposed in first and second cavities 53 and 54 respectively in the valving housing 12. The cavities 53 and 54 have cylindrical walls, FIG. 2 shows a cross-sectional view of the first and second electrostrictive cylinders 51 and 52 and the cavities 53 and 54. The electrostrictive cylinders 51 and 52 are electrically grounded to the valving housing 12 by electrically conductive leaf springs 55, such as Phosphor bronze springs, interposed between each of the cavities 53, 54 and the outer peripheral surfaces of the electrostrictive cylinders 51 and 52. As shown in FIGS. 2 and 6, the springs 55 may be spaced approximately 120 apart near each of the ends 56 and 57 of the electrostrictive cylinders 51 to insure a good electrical ground.

A portion of the electrostrictive means 50 is shown more in detail in FIG. 6. FIG. 6 shows in cross-sectional view the valve housing 12, the cavity .53 in the housing 12 and the electrostrictive cylinder 51 disposed in the cavity 53. The cylinder 51 is interposed between two resilient 0 rings 58 and 59 which provide a fluid seal at the ends 56 and 57 of the electrostrictive cylinder 51, While allowing for longitudinal and radial motion of the cylinder 51. The same type of sealing rings 58 and 59 are provided for the other electrostrictive cylinder in the cavity 54.

Interposed between the cavities 53 and 54 and the valving member 31 are the piston buttons 63 and 64 respectively which communicate the motivating force due to fluid pressure variations within the cavities 53 and 54 to the lever portion 44 of the valving member 31.

The piston buttons 63 and 64 are slidably disposed and in a sealing relationship within two cylindrical passages 8 and 9. The passages 8 and 9 are coaxially aligned and have their longitudinal axis transverse to the lever portion 44 the points and 71. The cylindrical passages 8 and 9 communicate with the cavities 53 and 54 respectivley. The fluid pressure variations in the cavity 53 are comcmunicated to the piston button 63 by a relatively small volume of captive fluid which is substantially confined by the volume bounded by the outer surface of the electrostrictive cylinder 51, the piston button 63 and the side wall and ends of the cavity 53. In a like manner, the fluid pressure variations in the cavity 54 are also communicated to the piston button 64 by a relatively small volume of captive fluid which is substantially bounded by the outer surface of the electrostrictive cylinder 52, the piston button 64 and the side wall and ends of the cavity 54. The small volume of the captive fluid in each of the cavities 53 and 54 is associated with a high acoustic stiflness so that the captive fluid behaves, by and large as an incompressible fluid. The piston buttons are free to move with respect to the cavities 53 and 54 and present a relatively low impendance to AC fluid pressure variations so that substantially all of the AC volume displacement generated by the motion of the electrostrictive cylinders provide equivalent displacement of the piston buttons.

The cavities 53 and 54 are connected to the high pressure side of the pump 20 at inlet 61 and 62 by way of inertance lines 90 and 91 respectively. The pump 20 maintains a constant steady (DC) fluid pressure in the cavities 53 and 54 and provides a biasing force on piston buttons 63 and 64 so that the pistons remain at all times in contact with the lever arm 44 at contact points 70 and 71. No fluid return is provided for the cavities 53 and 54 since the steady, DC pressure is maintained therein about which the AC fluid pressure, which is produced in the amplifier, varies. The inertance lines 90 and 91 have a small cross sectional area and present a high impedance to AC pressure variation generated in the cavities 53 and 54 and thus substantially prevent any AC volume current to be shunted away from the piston buttons.

The piston buttons 63 and 64 each have a relatively small area exposed to the captive fluid in each of the cavities '53 and 54 respectively as compared to the area of each of the electrostrictive cylinders 51 and 52. Small radial motions of the electrostrictive cylinders 51 and 52 of opposite sense cause a relatively high linear displacement of the piston buttons 63 and 64 along the the longitudinal axis thereof. The ratio of the linear displacements of the piston buttons 63 and 64 to the linear radial displacements of the electrostrictive cylinders 51 and 52 will equal approximately the ratio of the effective driving areas of the electrostrictive cylinders 51 and 52 to the driven area of the piston buttons '63 and 64. The combination of the electrostrictive cylinders with its respective fluid cavity and piston button forms a hydraulic transformer to enable a small linear motion of the cylinder surface to be transformed into a relatively larger motion of the piston button. This hydrualic transformer action coupled with the aforementioned rotary mechanical transformer action of the lever arm 44 and the valving arm 41 as referenced to the axis of rotation of shaft 32 allows a small linear motion of the surfaces of the electrostrictive cylinders 51 and 52 to be transformed into a large valving stroke of metering edge 42, and a correspondingly large variation in the area of orifice 49.

The large valving stroke magnification resulting from the transformer actions provides for eflicient power conversion, and effective flow control. Furthermore, the large valving stroke increases the power handling capacity of the amplifier.

The electrostrictive cylinders 53 and 54 are polarized so that an electrical signal vlotage applied across inner electrodes 65 and 66 and outer electrodes 67 and 68, these electrodes being provided by the coatings referred to above, of the electrostrictive cylinders 51 and 52 respectively will cause the cylinders 51 and 52 to move radially in a phase opposed sense so that the valving member 31 may be alternately rocked about the shaft 32 to vary the area of the orifice 49 and to control the flow of fluid from acoustic chamber 22 to the exhaust chamber 27.

FIG. 7 shows the electrical circuit 70 for the hydroacoustic amplifier 10. The electrostrictive cylinders 51 and 52 are illustrated as capacitors 51 and 52 since their electrical properties correspond to capacitors. The capacitors or electrostrictive cylinders 51 and 52 are grounded on one side which may be for example the valving housing 12 or by a lead wire 76 to ground by way of outer electrodes 67 and 68 on the electrostrictive cylinders 51 and 52. The inner electrodes 65 and 66 of the capacitors or electrostrictive cylinders 51 and 52 are connected to input terminals 73 and 74 respectively by lead wires 77 and 78. The electrical circuit 70 for illustrative purposes may be connected to an input signal source not shown by way of a coupling transformer 75 so that a signal applied to the coupling transformer 75 will give two electrical outputs which will be 180 out of phase with each other when applied to the capacitors or electrostrictive cylinders 51 and 52. A signal applied to coupling transformer 75 will thus cause electrostrictive cylinders 51 and 52, when polarized, to alternately expand and contract to increase and decrease the pressure in the cavities 53 and 54 respectively. When a plurality of amplifiers are connected in an array, say for underwater object detection or signalling, the input signals may be applied simultaneously or selectively, by way of suitable switching, to the input transformers of each amplifier.

The lead wires 76, 77 and 78 may extend through an insulating boot and a slot 81 in the valving housing 12. FIG. 6 shows a watertight insulated terminal '84 for lead wire 77. The terminal 84 is mounted in an end plug 85 which is bolted to the valving housing 12 as by bolts 86. A similar end plug not shown is provided for the other electrostrictive cylinder 52 and cavity 54.

A flexural disc radiating element 80 is shown in FIGS. 2 and 4, which is clamped to the chamber housing 13 by bolts 81. A piston 82 couples acoustic energy from the acoustic chamber 22 to the flexural disc radiating element 80. The acoustic signals produced by piston 82 are similar in waveform to the electrical input signals. Accordingly by applying electrical input signals in controlled phase relation to a plurality of amplifiers in an array thereof, acoustic signals which are directional in nature can be produced. Also the acoustic signals can have complex waveforms to represent information for signalling purposes.

In the operation of the hydroacoustic amplifier 10 the hydraulic fluid under pressure is fed from the pump 20 through the main feeder line 18 to the receiving chamber 24. The fluid is then fed through the inertance line 23 and the acoustic chamber 22 all of which define the acoustic tank circuit 21. In the unoperated condition the valving member 31 is normally in a zero lap position such that metering rim 42 of valving member 31 is in line with metering rim 48 of stator port 26. In this position a small leakage flow passes from chamber 22 through the clearance gap between the end surface 39 of valving member 31 and end surface 40 of stator port structure 26 to the exhaust chamber 27. The fluid from the exhaust chamber 27 flows into the main return line 29 through the outlet connection 28 to the input connection 30- of the constant delivery pump 20. The pump 20 maintains a constant steady or DC fluid pressure in the cavities 53 and 54. Thus, in the unoperated or quiescent condition there may be a small, steady leakage flow of fluid under pressure through the acoustic tank circuit 21, through the outlet stator port structure 26, the exhaus chamber 27 and back 0 the pump 20.

If an electrical signal is now applied through the transformer 75 to the electrostrictive cylinders 51 and 52, these cylinders will alternately expand and contract out of phase with respect to each other. The electrostrictive cylinder 51 for example, may expand radially during a positive phase of the signal to cause a positive-going pressure with respect to the average pressure in the fluid between the sidewall of the cavity 54 and the electrostrictive cylinder 52 so that the piston button 64, in response to the increased pressure in the cavity 54, exerts a positive force acting in a clockwise direction on the lever portion 44 of the valving member 31. During this same phase the other electrostrictive cylinder 51 may contract to cause a negative-going pressure with respect to the average pressure in the fluid in the other cavity 53. This negative-going pressure exerts a negative force acting through piston button 63 in a clockwise direction on the lever portion 44 of the valving member 31. In response to the net clockwise force exerted on the portion 44, the valving member 31 rotates in a clockwise direction to open the orifice 49 of the outlet stator port structure 26.

It can also be seen that the valving member 31 strokes to a closed position for orifice 49 during a negative phase of the signal when the electrostrictive cylinder 52 contracts and the electrostrictive cylinder 51 expands.

The valving member 31 may open the orifice 49 for 50 percent of the time for a given AC electrical signal voltage to give a single-ended class B opertion at the given frequency. Class A, B, or C operation may be obtained by adjusting the position of the valving member 31 relative to the outlet stator port structure 26 to allow the orifice 49 to be open for various time periods during a given period of the electrical input signal. This adjustment can be accomplished by loosening the clamping screws 35 and moving the valving member about the shaft 32.

The type or class of modulation in the hydroacoustic amplifier depends upon the average position of the metering edge 42 with respect to the rim 48 of the orifice 49. If the orifice 49 is open for substantially more than 50 percent of the period of the applied signal the hydroacoustic amplifier 10 operates in a single-ended class A manner. If the orifice 49 is open for approximately 50 percent of the period a single-ended class B operation is achieved. If the orifice 49 is open for less than 50' percent of the period of the applied signal, a single-ended class C operation is achieved. Furthermore, the output frequency of the amplifier 10 may be doubled by adjusting the travel of the valving member 31 to traverse the rectangular opening 43 twice during each cycle. 'In effect, the edge of the valving member opposite the metering edge 42 may now also serve to define another orifice with the outlet stator port structure 26.

For maximum power transfer, maximum efficiency, and minimum distortion in the output signal, the fundamental frequency of the modulated flow through orifice 49 at the mean frequency of amplifier operation should correspond simultaneously to the resonant frequency of the tank circuit 21 and the resonant frequency of the coupling structure 80. Although the instantaneous volume velocity through the orifice 49 for single-ended class B or C operation, may not be sinusoidal for a sinusoidal excitation signal voltage input, the acoustic filter action provided by the resonant tank circuit 21 and coupling structure 80 can insure that the signal transferred to the load is a non-distorted replica of the excitation signal voltage input.

Although two electrostrictive cylinders 51 and 52 have been shown, providing for a push-pull form of drive of the valving member 31, it is evident that one cylinder could be used to provide single-ended drive with the static or average biasing force exerted by the corresponding one piston button on the lever arm 44 supported by an average torsional deflection of the torsionsprings 37 and 38 of shaft 32.

From the foregoing description, it will be apparent that there has been provided an improved hydroacoustic amplifier suitable for use in underwater sound applications. Although one embodiment of the hydroacoustic amplifier has been described it will be appreciated that variations and modifications therein within the scope of the invention will undoubtedy become apparent to those skilled in the art. Accordingly, the foregoing description should be taken merely as illustrative and not in any limiting sense.

What is claimed is:

1. A hydroacoustic amplifier comprising (a) a chamber having an inlet and an outlet port structure for the flow of a fluid medium under pressure therethrough,

(b) a valving member operatively mounted in cooperative relationship with said outlet port structure for modulating the flow of said fluid medium output through said outlet port structure, and

(c) hydraulic transformer means coupled to said valving member and responsive to an applied electrical input signal for operating said valving member to modulate the flow of said fluid medium through said outlet port structure to thereby derive acoustic energy in said chamber, said hydraulic transformer means including an electromechanical transducer having a first surface which changes dimensions as a function of said signal, means coupled to said valving member having a second surface having an area different from the area of said first surface, said first and second surfaces being fluid coupled to each other.

2. The invention according to claim 1 further provided with means connected to said chamber for coupling said acoustic energy in said chamber to a load.

3. The invention according to claim 1 wherein said electromechanical transducer includes an electrostrictive cylinder disposed in a fluid filled cavity and wherein said means coupled to said valving member includes a movable piston button coupled to said cavity for transferring pressure variations in said cavity to said valving member.

4. The invention according to claim 3 wherein said electrostrictive cylinder has a greater surface area than the cross sectional area of said piston button so that a small radial expansion of said electrostrictive cylinder in response to a signal voltage applied thereto produces a high linear displacement of said piston button away from said cavity.

5. In a hydroacoustic amplifier, the combination comprising (a) a chamber having an outlet port structure and an inlet for the flow of a fluid medium under pressure therethrough,

(b a valving mmeber operatively mounted in cooperative relationship with said outlet port structure for selectively modulating the flow of said fluid medium through said chamber, and

(c) hydraulic means coupled to said valving member and responsive to an applied electrical input signal of variable frequency and amplitude for controllably operating said valving member to selectively modulate the flow of said fluid medium through said outlet port structure to thereby derive in said chamber acoustic energy having a frequency and amplitude corresponding to said variable frequency and amplitude.

6. The invention defined in claim 5 wherein said valving member is connected in cooperative relationship with said hydraulic means to modulate the flow of said fluid medium through said outlet port structure at twice the frequency of said electrical input signal.

7. In a hydroacoustic vibration amplifier the combination comprising (a) a chamber having an inlet and an outlet port structure for the flow of a fluid medium under pressure therethrough,

(b) first means including at least one valving member resiliently mounted in cooperative relationship with said outlet port structure for modulating the flow 'of said fluid medium through said chamber, and

(c) hydraulic means coupled to said valving member and responsive to an applied electrical input signal having a frequency falling within a given broad band of frequencies for selectively operating said valving member,

(d) said valving member having a resonant frequency falling within said given broad band of frequencies.

8. A hydroacoustic amplifier comprising (a) an acoustic chamber having an outlet port structure and an inlet for the flow of a fluid medium under pressure therethrough,

(b) a normally open valving member coupled to said outlet port structure to modulate said flow of said fluid medium through said acoustic chamber when operated,

(c) at least one cavity adapted to contain a fluid under pressure,

(d) coupling means communicating with said valving member and said cavity for transmitting pressure variations in said one cavity to operate said valve, and

(e) means including an electrically responsive device which changes dimensions in all directions in response to an electrical voltage partially filling said one cavity to introduce pressure variations in said one cavity to operate said valving member so that acoustic energy is generated in said acoustic chamher when said valving member is operated.

9. In a hydroacoustic amplifier having a valving member for modulating the flow of a fluid medium under pressure for the generation of acoustic energy when said valving member is vibrated, apparatus for vibrating said valving member comprising:

(a) ahousing,

(b) at least one cavity disposed in said housing and adapted to contain a fluid under Pressure therein,

(c) an electrically responsive device which changes dimensions in response to an electrical voltage applied thereto,

(d) said electrically responsive device partially filling said cavity whereby pressure variations are introduced in said cavity when said electrical voltage is applied thereto, and

(e) means including a movable piston button communicating with said cavity for vibrating said valving member in response to pressure variations within said cavity.

10. The invention defined in claim 9 wherein said electrically responsive device is an electrostrictive element.

11. The invention defined in claim 9 wherein said electrically responsive device is an electrostrictive cylinder.

12. The invention defined in claim 9 further including means for maintaining a steady fluid pressure within said cavity about which said pressure variations are introduced in said cavity by said electrically responsive device.

13. The invention defined in claim 9 wherein said electrically responsive device has a larger surface exposed in said cavity than said movable piston button.

14. In a hydroacoustic amplifier having a valving memher for modulating the flow of a fluid medium under pressure for the generation of acoustic energy when said valving member is vibrated, apparatus for vibrating said valving member comprising (a) ahousing,

(b) first and second cavities disposed in said housing and adapted to contain a fluid under pressure therein,

(c) first and second electrostrictive elements partially filling said first and second cavities respectively,

(d) means for applying an electrical signal in phase opposition to said first and second electrostrictive elements to alternately induce positive and negative going changes in dimensions in said first and second electrostrictive cylinder respectively, to induce corresponding fluid pressure variations in said first and second cavities, and

(e) means including first and second movable piston buttons exposed to said fluid in said first and second cavities respectively at one end thereof and coupled to said valving member at the other end thereof for communicating pressure variations in said first and second cavity to said valving member.

References Cited UNITED STATES PATENTS 2,161,980 6/1939 Runge et al 3108.2 2,454,264 11/1948 Stigter 340-10 2,498,737 2/ 1950 Holden 310-9.6 2,991,594 7/1961 Brown et a1. 51--59 3,105,460 10/1963 Bouyoucos 116--137 3,143,999 8/1964 Bouyoucos 116137 3,212,472 10/ 1965 Bouyoucos 116-137 3,212,473 10/1965 Bouyoucos 116-137 3,267,421 8/1966 Robinson et al 3408 X 3,349,367 10/1967 Wisotsky 340 -8 X RODNEY D. BENNETT, JR., Primary Examiner B. L. RIBANDO, Assistant Examiner US. Cl. X.R. 181.5

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