US3354426A

US3354426A - Pressure gradient hydrophone

Info

Publication number: US3354426A
Application number: US523780A
Authority: US
Inventors: Massa Frank
Original assignee: Dynamics Corp of America
Current assignee: Dynamics Corp of America
Priority date: 1966-01-28
Filing date: 1966-01-28
Publication date: 1967-11-21
Anticipated expiration: 1984-11-21

Description

Nov. 21, 1967 F. MASSA 3,354,426

PRES SURE GRADIENT HYDROPHONE Filed Jan. 28, 1966 INVENTOR j FRANK MASSA ATTORNEY United States Patent i 3,354,426 Patented Nov. 21, 1967 ice Mass.

Filed Jan. 28, 1966, Ser. No. 523,780 11 Claims. (Cl. 340-10) This invention is a continuation-in-part of my copending application Serial No. 481,809, led August 23, 1965, which discloses a pressure gradient hydrophone that will operate satisfactorily throughout the lower portion of the audible frequency region. The novel design of that application also provides for an equalization of the hydrostatic pressure before the pressure is transferred to the active transducer element so that the hydrophone is capable of operation when it is immersed in deep water.

This invention relates to pressure gradient transducers and more particularly to pressure gradient transducers usable as hydrophones to be positioned underwater at relatively great depths. The transducers of this invention are relatively simple in construction and operation, are readily and inexpensively manufacturable while being rugged and reliable in operation, with excellent response characteristics and sensitivity, particularly at extremely low frequencies.

The present invention achieves the same objects as set forth in the aforesaid copending application and has in addition the further object of providing increased sensitivity at extremely low frequencies.

According to an important feature of the invention, connection means are provided between diaphragm means which sealingly close opposite ends of a generally tubular housing and an end portion of transducer means movable axially within the housing with the other end of the transducer means being secured to an intermediate point in the housing. Preferably, the transducer means is in the form of a cantiliver beam. With this arrangement, a very simple construction is provided with an equalization of hydrostatic pressure such that the transducer can be immersed in deep water, and increased sensitivity is obtained particularly at extremely low frequencies.

In accordance with a specific feature of the invention, the movable end of the transducer means is positioned beyond a center line of the tubular housing and generally U-shaped yoke means are provided having a bight portion secured to the movable end of the transducer means and having a pair of leg portions extending to the center line, with a pair of means extending along the center line connecting the leg portions to the diaphragm means. Preferably, the transducer means has a length dimension which is substantially greater than the width dimension thereof. With these features, a relatively long narrow transducer means results, to further increase sensitivity at extremely low frequencies while obtaining pressure equalization.

In accordance with further features of the invention, the transducer means comprises a multilaminar plate assembly at least one element of which comprises a transducer material capable of converting oscillatory mechanical stresses to alternating electrical signals. Preferably, at least one plate of a polarized ceramic material is used.

In certain preferred embodiments of the invention, a pair of polarized plates are used having faces of one polarity in facing relation. In one of such embodiments, thin electrodes on the inward faces of the aforesaid one polarity are bonded together, while in another embodiment, a metallic plate is provided sandwiched between the transducer plates, having an inner end portion secured to an intermediate point of the housing and having an opposite end portion mechanically coupled to the dia- A phragm means.

In another embodiment of the invention, the transducer means comprises a single plate of piezoelectric material and a supporting plate bonded to one face of the plate of piezoelectric material.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate preferred embodiments and in which:

FIGURE l is a longitudinal sectional view of one preferred embodiment of a pressure gradient hydrophone constructed according to the principles of this invention;

FIGURE 2 is a sectional view taken substantially along line II-II of FIGURE 1;

FIGURE 3 is a plan view of a modied form of transducer assembly usable in place of that shown in FIG- URE 1;

FIGURE 4 is a sectional view taken substantially along line VI-VI of FIGURE 3; and

FIGURE 5 is a sectionalview similar to FIGURE 4, but illustrating another modified form of transducer assembly according to the invention.

Referring to FIGURE 1, reference numeral 10 generally designates a pressure gradient hydrophone constructed in accordance with the principles of this invention. The hydrophone 10 comprises transducer means 11 disposed within a generally tubular housing structure which is generally designated by reference numeral 12, with vibratile diaphragm means 13 and 14 sealingly closing opposite ends of the tubular housing structure 12 and mechanically coupled to the transducer means 11, by means including a pair of rods 15 and 16 extending along the central axis of the housing means 12. l

The transducer means 11 comprises two

plates

17 and 18 of piezoelectric material, preferably polarized barium titanate or polarized lead zirconate titanate which are bonded together, with one end. of the assembly being cemented against both an internal annular shoulder 19 and an internal generally cylindrical surface 20,of .a ring 21 forming an intermediate part of the housin structure 12.

The other end of the transducer assembly 11 is movable axially within the housing structure 12 and is mechanically coupled to the diaphragm means 13 and 14'through the rods 15 and 16. Preferably, and in accordance with an important feature of the invention, the mechanical coupling means comprises a generally U-shaped yoke 23 having a bight portion 24 cemented to the movable end of the transducer assembly, and having

leg portions

25 and 26 extending to the center line of the housing structure 12 and having openings for receiving reduced

diameter pin portions

27 and 28 at the ends of the rods 15 and 16. With this arrangement, the movable end of the transducer assembly 11 extends Well beyond the cenvter line of the housing structure 12 and, as shown in FIGURE 2, the width of the transducer assembly is less than the length thereof, these features cooperating to increase the sensitivity of the hydrophone at extremely low frequencies.

As indicated by the plus and minus signs in FIGURE 1, the inner facing surfaces of the polarized

transducer plates

17 and 18 are of the same polarity (a negative polarity as indicated on the drawing), and

thin electrodes

29 and 30 formed on such inner facesare bonded together.

Electrodes

31 and 32 are provided on the outer faces of the

transducer plates

17 and 18, which are also of the same polarity (a positive polarity as indicated on the drawing), and

such electrodes

31 and 32 are connected to wires 33 and 34 extending through

insulated bushings

35 and 36 in the wall of the ring 21.

The wires 33 and 34 form terminal means for connection of the hydrophone -to a suitable amplifier. With the described polarization of the

transducer plates

17 and 18, the combined series voltages across both plates are additive when the movable end of the transducer assembly is deflected in response to movements of the diaphragm means 13 and 14.

In addition to the intermediate ring 21, the housing structure 12 comprises a pair of

tubular members

37 and 38 with an inner end portion 39 of member 37 being tightly fitted on a reduced diameter portion 40 at one end of the ring 21 and with a reduced diameter portion 41 at the inner end of member 38 being fitted within the other end of the ring 21.

The diaphragm means 13 and 14 are in the form of circular end plates or caps disposed tightly against the end of the

tubular members

37 and 38 and having annular grooves on the inside surfaces thereof to define relatively

thin webs

43 and 44 which provide a exural suspension for

central piston portions

45 and 46 connected to the ends of the rods and 16, the rods 15 and 16 preferably having reduced

diameter end portions

47 and 48 extending into openings in the center of the

piston portions

45 and 46.

An epoxy cement is preferably employed at each joint where the mechanical parts are attached together, to make a permanent, rigid, waterproof bond.

Referring to FIGURES 3 and 4, reference numeral 50 generally designates a modied transducer and yoke assembly which may be substituted for the transducer means 11 and the yoke 23 of the hydrophone of FIGURE 1. In the assembly 50, a piezoelectric plate 51 is provided, which may preferably ybe polarized barium titanate or polarized lead zirconate titanate, for example. The plate 51 has an electrode 52 on one face thereof and a pair of

separate electrodes

53 and 54 on the other face thereof, a longitudinally extending relatively narrow gap being provided between the

electrodes

53 and 54 to which leads 55 and 56 are secured. The plate 51 is bonded to a plate 58 which may be of aluminum or some other suitable material, preferably |by means of a rigid cement such as epoxy which preferably also serves to insulate the electrode 52 from the surface of the plate 58. The plate 5S has an vend portion adapted to be cemented or otherwise secured to the shoulder 19 and surface 20 of the ring 21 and an opposite movable end portion 60 which is disposed between legs of a pair of L-

shaped members

61 and 62 to form a yoke, with a rivet 63 extending through the legs of the

members

61 and 62 and the portion 60. The other legs of the L-

shaped members

61 and 62 have

openings

65 and 66 for receiving the reduced

diameter portions

27 and 28 of the rods 15 and 16.

The plate 51 may be polarized =by applying a positive voltage on electrode 53 and a negative voltage on electrode 54 with a center tap from the polarizing voltage being connected to the electrode 52 on the opposite side of the plate 51, the plate 51 being cemented on the plate V58 after polarization. When the assembly 50 is then installed in place of the transducer means 11 and yoke 23 in the arrangement of FIGURE 1, an alternating force acting on the diaphragms 13 and 14 will set up a vibra- -tion of the end 60 of the plate 58 and alternating additive voltages will be generated across the sections to which

electrodes

53 and 54 are attached, to develop an AC signal between the

conductors

55 and 56.

Referring now to FIGURE 5, reference numeral 68 generally designates another form of transducer and yoke assembly which may be substituted for the transducer means 11 and yoke 23 of the arrangement of FIGURE 1. In theassembly 68, a plate 70 of aluminum or some other suitable material is provided, similar to the plate 58 of the assembly 50 of FIGURES 3 and 4, and having an end 7,1 adapted to be cemented or otherwise secured to the shoulder 19 and internal surface 20 of the ring 21 and having an opposite movable end 72 disposed between the legs of two L-

shaped members

73 and 74 with a rivet `7,5 extendihg through legs of the

members

73 and 74 and the end portion 72 of the plate 70, and with

openings

77 and 78 in the other legs of the

members

73 and 74 for receiving the reduced

diameter portions

27 and 28 of the the rods 15 and 16. In this arrangement, an intermediate portion of the plate 70 is sandwiched between two transducer plates 79 and 80 having polarizations similar to the polarizations indicated in FIGURE 1.

Electrodes

81 and 82 on the outer surfaces of the plates 79 and 80 are connected to

conductors

83 and 84, while

electrodes

85 and 86 on the inside surfaces of the plates 79 and 80 are cemented to the plate 70, preferably by means of an epoxy cement, and preferably with the cement serving to electrically insulate the

electrodes

85 and 86 from the opposite surfaces of the plate 70.

The illustrated ararngements operate in a manner similar to those disclosed in my copending application Serial No. 481,809, filed August 23, 1965. The basic difference in result is that the arrangements of this application are particularly adapted for increased sensitivity at extremely low frequencies. When operation of the pressure gradient hydrophone is desired at the lowest portion of the audible frequency range and where high frequency operation is not essential, the increased sensitivity can be obtained with the arrangements disclosed in this application. The hydrophone will have maximum sensitivity for sound arriving along an axis parallel to the normal axis of the cylindrical structure. For any sound arriving along the path which at right angles to the axis of the hydrophone, the instantaneous sound pressure will be of the same magnitude and phase on the surface of each diaphragm, and, therefore, 0 voltage will be generated by the hydrophone. For sound arriving at angles |between 0 and 90, the sensitivity will be proportional to the cosine of the angle which the axis of the sound source makes with the axis of the hydrophone.

Although I have chosen only a few examples to illustrate the basic principles of my invention, it will be 0bvious to those skilled in the art that numerous departures may be made from the details shown, and I, therefore, desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the `Spirit of the appended claims.

I claim as my invention:

1. In combination in a pressure gradient transducer, generally tubular housing means, end plates on opposite ends of said housing means having annular grooves therein defining relatively thin webs for liexural suspension of central piston portions thereof, transducer means comprising a multilaminar plate assembly with at least one element of said plate assembly comprising a transducer material capable of converting oscillatory mechanical bending stresses to alternating electrical signals, means for rigidly supporting one end of said multilaminar plate assembly at a point within said housing means intermediate said end plates to position the opposite end of said assembly beyond a center line of said tubular housing means, U-shaped yoke means having a bight portion secured to said opposite end of said assembly and having a pair of leg portions extending to said center line, a pair of rigid rods extending along said center line and rigidly connected to said central piston portions of said end plates and to said leg portions of said yoke means, and electrical terminal means for connecting said transducer material to an external circuit.

2. In combination in a pressure gradient transducer, generally tubular housing means, vibratile diaphragm means sealingly closing opposite ends of said housing means, a somewhat elongated transducer means having two end portions, said transducer being sealed within said housing means, one of said end portions being secured to a point in said housing means intermediae said opposite ends, the opposite end portion being free to move axially in said elongated dimension within said housing means, and connection means extending through said housing and rigidly attached between the diaphragm means fpr mechanically coupling said opposite end portion to said diaphragm means.

3. In a pressure gradient transducer as defined in claim 2, said transducer means being in the form of a cantilever beam.

4. In a pressure gradient transducer as defined in claim 2, said transducer means comprising a multilaminar plate assembly with at least one elementl of said plate assembly comprising a transducer material capable of converting oscillatory mechanical stresses to alternating electrical signals, and electrical terminal means connected to said transducer material.

5. In a pressure gradient transducer as defined in claim 2, said transducer means having a length dimension as measured in a direction between said one end and said opposite end which is many times greater than a width dimension as measured in a direction transverse to said length direction.

6. In a pressure gradient transducer as defined in claim 2, said transducer means comprising a plate of a polarized ceramic material.

7. In a pressure gradient transducer as deined in claim 2, said transducer means comprising a pair of plates of polarized ceramic material having faces of one polarity in facing relation, electrode means on said faces of said one polarity, electrodes on the opposite faces of said plates, and electrical terminal means connected to said electrodes on said opposite faces of said plates.

8. In a pressure gradient transducer as defined in claim 7, said electrodes on said faces of said one polarity being directly bonded together.

9. In a pressure gradient transducer as dened in claim 7, a supporting plate sandwiched between said faces of said plates of said one polarity and having one end portion secured to said intermediate point in said housing means and an opposite end portion defining said opposite end portion which is mechanically coupled to said diaphragm means.

10. In combination in a pressure gradient transducer, generally tubular housing means, vibratile diaphragm means sealingly closing opposite ends of said housing means, transducer means within said housing means having one end portion secured to a point in said housing means intermediate said opposite ends and having an opposite end portion movable axially within said housing means, said transducer means comprising a multilaminar plate assembly with at least one element of said plate assembly comprising a transducer material capable of converting oscillatory mechanical stresses to alternating electrical signals, electrical terminal means connected to said transducer material, connection means mechanically coupling said opposite end portion to said diaphragm means, said opposite end portion of said transducer means being positioned beyond a center line of said tubular housing means, and said connection means comprising generally U-shaped yoke means having a bight portion secured to said opposite end of said transducer means and having a pair of leg portions extending to said center line and a pair of means extending along said center line connecting said leg portions to said diaphragm means.

11. In combination in a pressure gradient transducer, generally tubular housing means, vibratile diaphragm means sealingly closing opposite ends of said housing means, transducer means within said housing means having one end portion secured to a point in said housing means intermediate said opposite ends and having an opposite end portion movable axially Within said housing means, connection means mechanically coupling said opposite end portion to said diaphragm means, said transducer means defining a plate lof piezoelectric material and a supporting plate bonded to one face of said plate of piezoelectric material and having one end portion secured to said intermediate point in said housing means and an opposite end portion defining said opposite end portion which is mechanically coupled to said diaphragm means, a pair of electrodes on separate portions of the opposite face of said plate of piezoelectric material, said piezoelectric material being a polarized ceramic material with the portions on which said pair of electrodes are attached being oppositely polarized, and terminal means connected to said pair of electrodes.

References Cited UNITED STATES PATENTS 2,497,672 2/ 1950 Jaffe. 2,647,162 7/ 1953 Duncan. 2,659,829 11/1953 Baerwald 340-10 X RODNEY D. BENNETT, Primary Examiner. CHESTER L. JUSTUS, Examiner B. L. RIBANDO, Assistant Examiner.

Claims

1. IN COMBINATION IN A PRESSURE GRADIENT TRANSDUCER, GENERALLY TUBULAR HOUSING MEANS, END PLATES ON OPPOSITE ENDS OF SAID HOUSING MEANS HAVING GROOVES THEREIN DEFINING RELATIVELY THIN WEBS FOR FLEXURAL SUSPENSION OF CENTRAL PISTON PORTIONS THEREOF, TRANSDUCER MEANS CONPRISING A MULTILAMINAR PLATE ASSEMBLY WITH AT LEAST ONE ELEMENT OF SAID PLATE ASSEMBLY COMPRISING A TRANSDUCER MATERIAL CAPABLE OF CONVERTING OSCILLATORY MECHANICAL BENDING STRESSES TO ALTERNATING ELECTRICAL SIGNALS, MEANS FOR RIGIDLY SUPPORTING ONE END OF SAID MULTILAMINAR PLATE ASSEMBLY AT A POINT WITHIN SAID HOUSING MEANS INTERMEDIATE SAID END PLATES TO POSITION THE OPPOSITE END OF SAID AS-