US3760346A

US3760346A - High-power underwater electroacoustic transducer for the infrasonic and low audio-frequency range

Info

Publication number: US3760346A
Application number: US00251410A
Authority: US
Inventors: J Donovan; R Kieser; J Bass
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1972-05-08
Filing date: 1972-05-08
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18
Also published as: CA966928A

Abstract

This disclosure is directed to a high power underwater electroacoustic transducer operable in the infrasonic and low audiofrequency range.

Description

1101M States Pafienfi 1 1 1111 3,760,346

Kieser et al. 1 Sept. 18, 1973 [5 HIGH-POWER UNDERWATER 1,808,149 6/1931 Smith 340 12 R ELECTROACOUSTIC TRANSDUCER FOR 3,823,282 13:32; 3611mm gig/1:31 g

, a meyer THE INFRASONIC AND Low 3,345,607 /1967 Nelkin et al. 340/8 PC A[mm-FRI)UENCY RANGE 2,404,360 7 1946 Bostwick 340 14 2,490,595 12 1949 Merten 340 13 R Invfimors' 5E123; 3} 6323i; 0 2,429,104 10/1947 OISOn 340/13 R Fla 3,394,775 7/1968 C016 et al 340 12 R [73] Assignee: The United States of America as represented by the Secretary of the Primary ExaminerBenjamin A. Borchelt Navy Assistant ExaminerH. J; Tudor ,7 t l. Filed: y 1972 Attorney R S Sc1asc1ae a [2]] App]. No.: 251,410

[57] ABSTRACT [52] U.S. Cl. 340/8 R, 340/17 1 This disclosure is directed to a high power underwater e 0 care electro-acoustic transducer operable in the infrasonic and low audlo-frequency range.

[56] References Cited 7 UNITED STATES PATENTS 2 Cl 6 D 3,113,125 1 1964 Sims 340/8 rawmg gums 111 5G 55 H3 o 43 a2 35 22 I06 as B6 92 as 1 5 z t 4 23 B4 L 71 3 i 2 H I 73 15 q 7B 75 9 99 52 a1 17 14 1e PATENTEU SEP1 81975 SHEET 2 [if d PATENTEI] SEP1 8I975 SHEEI 30F 4 PATENTED 3.760. 346

SHEET u n; a

FIG. 6.

HIGH-POWER UNDERWATER ELECTROACOUSTIC TRANSDUCER FOR THE INFRASONIC AND LOW AUDIO-FREQUENCY RANGE BACKGROUND OF THE INVENTION This invention is directed to underwater transducers and more particularly to an electro-acoustic transducerv operable in the infrasonic and low audio-frequency range.

Heretofore, transducers have been provided to meet specific needs; that is, specific transducers have been used for specific ranges of operation thereby requiring many different types of transducers to cover a wide frequency range. Prior art transducers have inherent limitations such as narrow range of frequency response, low maximum power input level, low available sound pressure level, fragile moving parts, limited depth capability, and large size and massive construction. Further, they require considerable effort and time for disassembly for repairs or replacement of parts.

SUMMARY OF THE INVENTION The transducer made in accordance with the teaching of the present invention is small in size, operable in shallow or deep water over a wide range of frequencies. The transducer includes in combination a magnet mass and a moving coil. A movable piston having the moving coil/coil form secured thereto is secured in position by compliant material and is provided with a piston centering pin coaxial with the magnet which keeps the moving coil centered in the magnetic gap throughout the entire length of the piston displacement. Suitable stops are provided to limit the travel of the piston. The piston is surrounded with a suitable oil or other such fluid which transmits motion to or for the surrounding water.

STATEMENT OF THE OBJECTS It is therefore an object of the present invention to provide a transducer which has a high acoustic output over a broad low frequency band.

Another object is to provide a transducer in which the output is nearly linear with input over a broad frequency band.

Yet another object is to provide a transducer which is easily assembled and disassembled for replacement of parts or to make repairs.

Still another object is to provide a transducer which is sufficiently small that a family of transducers, each of which have different characteristics, may be assembled into a unitary structure to provide a very wide range of electroacoustic characteristics.

While still another object is to provide a transducer assembly which includes an efficient cooling system which allows high driving currents.

These and other objects will be better understood with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cut-away view illustrating the relative parts of a preferred transducer.

FIG. 2 illustrates a front view of the back pole piece.

FIG. 3 is a cross sectional view of FIG. 2 taken along lines 3-3.

FIG. 4 is a front view of the outer front pole piece.

FIG. 5 is a cross sectional view of the outer front pole piece.

FIG. 6 is a partial view illustrating a modification of the device shown in FIG. ll.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawing, there is shown by illustration in FIG. 1 a transducer element made in accordance with the teaching of the present invention. The transducer element includes a centrally located, grain oriented ALNICO V-7, dual diameter magnet 10 formed by solid sections 11 and 12 provided with an uniform coaxial aperture 13' therethrough. The magnet section 12 is provided with a cutout about the aperture to form a shoulder 14. A cylindrical magnetic ingot iron front pole piece 15 is secured to the front face of section 12 and is provided with a section 16 that fits into the cutout in the face of section 12 and rests upon the shoulder 14. The front pole piece has a central aperture colinear with the aperture in the magnet and is cutout on the front face about the aperture to provide a shoulder 17. The outer diameter of the front pole piece is the same as that of the magnet pole section 112.

A soft iron back pole piece 18 having a copper coating of LOOD ZSinch thereon is secured to the back face of magnet section 11. The back pole piece has a central aperture in alignment with the aperture in the magnet with the aperture 19 increasing toward the back on the radius of a circle which is less than the thickness of the pole piece. The back pole piece has a section 211 at a 45 angle which extends to a cylindrial section 22 that extends toward the front surrounding the magnet 10 and is spaced therefrom. The front face of cylindrical section 22 is on the same plane as the front face of section 12 of the magnet. The cylindrical section is provided with two equally spaced axially aligned apertures 23 therethrough through which electrical conductors are passed and eight apertures 24 through which bolts pass to secure the pole piece in place. Eight holes 25 are drilled near the front end perpendicular to the axis through which fluid may flow from one side of the magnet to the other, as shown in FIGS. 2 and 3. The 45 angle section is provided with oppositely disposed apertures 26 within which electrical terminals are secured to provide an electrical connection between a charging coil 27 in the spacing betweenthe magnet and the cylindrical portion of the back pole piece. The magnetic back pole piece is further provided with suitable threaded

holes

28 and 29 on the front and back sides respectively, for securing other elements to the magnetic pole piece.

The spacing between the magnet 10 and the cylindrical portion of the back pole piece 22 includes therein the charging coil 27 formed by approximately 51 turns of No. 13 A.W.G. type KZSFX heavy insulation class 200 magnetic wire. The coil is shown formed by three coils one over the other each having an 0.015 inch fibre insulation therebetween. The ends of the coil are secured to suitable terminals secured in the apertures 26 through the back pole piece. The remaining spacing between the magnet 10 and the cylindrical'portion of the and back pole piece are properly aligned. The centering ring further serves to make the unit more rugged, and the lead-epoxy potting compound damps spurious resonances and increases the mass of the static system. The centering ring 31 is also provided with cutouts that align with the apertures 25 in the back pole piece to aid in allowing the fluid flow through the apertures 25.

The cylindrical section of the back pole piece has secured thereto an outer front pole piece 32 by use of suitable bolts which pass through apertures 24 in the back pole piece and are threaded into appropriate threaded holes in the outer front pole piece. The outer front pole piece is of cylindrical shape and surrounds the inner front pole piece 15 secured onto the magnet 10. The inner front face 33 of the outer front pole piece as shown in FIGS. and 6 has a flat surface which is parallel with the surface of the inner front pole piece and spaced therefrom. The back face of the outer front pole piece has a circular groove 34 therein which receives an o-ring 35 and a circular protrusion 36 whose diameter is slightly less than the inner diameter of the cylindrical portion 22 of the back pole piece such that the end of the cylindrical portion of the back pole piece just slips over the protrusion when assembled. The

outer surface of the outer front pole piece is in the form of

steps

37 and 38 such that portions of the element is of greater diameter than the others. The step 37 has notches 41 therein and the steps 38 is provided with a groove 42 within which an o-ring seal 43 is placed. The element is provided with angularly drilled apertures 44 which extends outward toward the back to meet with the parallel apertures 23 in the back pole piece through which electrical conductors 45 are passed to an electrical terminal 46 secured within the aperture 44 as shown in FIGS. 1 and 6. A plurality of axially aligned parallel apertures 47 extend through the element near the inner surface through which fluid may flow from the front of the element to an area to the back thereof. An aperture may be drilled through the element to the back side thereof through which a heat pipe may be passed to aid in cooling the transducer. The cooling system is not shown for clarification of the drawings. The back side of the element is provided with threaded holes 51 between the groove 34 and the protrusion 36 to which an oil seal ring 52 is secured and threaded holes 53 outwardly of the protrusion by which the outer front pole piece is secured to the back pole piece by suitable bolts that pass through apertures 24 in the back pole piece. The portion of the element that has the greatest diameter has threaded holes 54 therein directed from the front surface by which the magnet assembly is secured within the housing by use of a cylindrical compression gasket 55 which is forced by a plurality of bolts 56 between the housing and the step 37 of the outer front pole piece. The front face is also provided with threaded holes 50 for securing a piston protection cage and holes 60 for securing an acoustic window assembly.

A piston 61 operated by a voice coil 62 positioned between the front outer and inner pole pieces is secured in place by a single ring-like compliant member 63. The compliant member is vulcanized to the brass oil seal ring 52 which is provided with a V-groove 64 for reception of the outer edge of the compliant member. The brass ring is provided with a plurality of apertures 65 through which screws 66 pass to secure the brass ring to the back surface of the outer front pole piece against the o-ring 35 placed in the groove within the surface of the outer front pole piece. The opposite end of the compliant member is secured to one end of an aluminum coil form 68 which is provided with a cutout section 71 about which the voice coil 62 is wound. The opposite end of the voice coil form is secured to the piston.

The voice coil comprises 208 turns of 30 AWG type KZSFX single insulation class 200 magnetic wire 69 wound in four rows or layers of fifty two turns each. The voice coil form 68 is placed on a mandrel, a coating of high temperature epoxy adhesive is applied to the surface of the form about which the coil is to be wound. The first layer is wound, then a second coat of epoxy adhesive is applied, etc, until the four layers are wound on the coil form and the outer layer coated. While rotating the finally wound coil, apply some heat such as a sun lamp to set the epoxy adhesive. After the adhesive has set, the coil may be heated in an oven to cure the coating. The coil form is provided with oppositely disposed grooves 70 along the length of the coil form toward the front within which the wire leads lay in order to conect the wire ends to electrical terminals secured to the piston without extending past the outer radius of the coil form.

The piston is formed by a cylindrical section 71 and a closed end nose portion 72 that is perpendicular to the axis of the device joined together by a conical section 73. The nose is provided with an axially aligned cylindrical hollow piston centering pin 74 which extends toward the aperture through the magnet. The front inner pole piece on the magnet has an axially aligned cylindrical piston guide 75 secured thereto coaxial with the piston. The piston guide is provided with an aperture through which the piston centering pin 74 passes and apertures 77 in the wall thereof through which fluid may flow. A portion of the inner surface of the piston guide is provided with a teflon bushing 78 through which the piston centering pin 74 operates. The bushing is held in place by a set screw 79. The bushing and a chromium plated sleeve 81 on the outside of the piston centering pin reduces friction during movement of the piston. A compliant, piston limiting stop 82 is secured to the end of the piston guide to limit the inward piston travel. The outward travel is limited by a stop 83 on a support cage 84 outwardly of the piston. The support cage is secured by suitable screws 76 to the outer front pole piece which thread into threaded holes 50. Movement of the piston is controlled by an electrical current which is applied to the voice coil thereby producing a magnetic reaction between the voice coil and the permanent magnet assembly.

The device operates in an oil or other suitable fluid filling which both cools and transmits the effects of sound waves between the surrounding medium and the piston. The oil is contained by end brass cylinder 86 and a rubber front window 87 secured thereto by any suitable method such as by vulcanization. The brass cylinder is provided with an outwardly extending flange 88 which is provided with a plurality of apertures therethrough by which it is secured to the outer front pole piece by use of suitable screws. The flange extends outwardly even with the step portion 37 on the outer front pole piece.

For protection of the window, a cage formed of 3/16 inch rod 89 welded to a ring 90, may be secured in place to the outer front pole piece outwardly of the end brass cylinder. As shown, the outer front pole piece and magnetic assembly are secured within the housing by use of the compression gaskets 55 which are compressed by bolts 56 which are threaded into the holes 54 in the outer front pole piece. Tightening of the bolts forces the compression gasket outwardly against the inner wall of the housing against the outer face of flange 88 and a portion of the outer front pole piece thereby holding the assembly in the housing.

The end brass cylinder 86 is provided with a threaded aperture 91 therein through which oil may be poured to fill the enclosed area. A plug 92 is used to plug the aperture 91. The oil may flow into the area behind the outer front pole piece through the small apertures 47 bored through the outer front pole piece and the magnet gap within which the piston moving coil is positioned. The apertures and the magnetic gap are kept small to keep acoustic energy from being shunted to the rear of the front pole piece.

The central aperture through the magnet is closed at both ends by

acoustic resistors

96 and 97 and by

diffusion plates

98 and 99, in order to minimize unwanted air-cavity resonances. The sonic resistors are made of a stainless steel fiber metal manufactured by Huyck Metal Company, Milford, Conn. This material permits air to filter through from one side of the magnet assembly to the other. The diffusion plates are spaced from the

acoustic plates

96 and 97 by a spacer 100 which permits air to flow between the acoustic-plate and the diffusion plate. The diffusion plate minimizes interference from the housing cavity.

The back end of the transducer housing is closed by a brass plate 101 which is secured in the end of the housing by screws 102 around the outside of the housing. The brass plate is provided with oppositely disposed apertures 103 near the housing wall to permit water to enter the area between the plate and a compliant pressure compensating bag 104. The compensating bag is secured about a plate extension 105 by use of a pressure band 106 or any other suitable means. An 0- ring 107 is placed between the back plate and the inner surface of the housing to prevent water leakage into the inner area of the housing.

The housing is provided with a water proof electrical connector 111 through which the required electrical conductors are brought and connected to an electrical terminal 112. The housing is also provided with a valve 113 through which air or other fluid may be added to the back side of the magnet for equalization of the inner and outer pressures during use.

All areas in which o-ring seals should be used to prevent fluid leakage from one area to another have not been particularly set forth. it is considered to be within the skill of one in the art to place an o-ring or other type seal where necessary without resorting to invention. Therefore, one should place an o-ring or other seals where necessary even though they have not been specifically setv forth in the specification. The drawings are believed to adequately illustrate the use of such 0- rings.

FIG. 6 illustrates a modification of the device shown in FIG. I. it has been determined, if desired, that instead of using the front window and sidewall cavity or brass cylinder, the corrugated rubber front window may be molded directly to the outer surface of the piston. in this modification, a short cylinder 121 is secured in place by the compression gasket and a corrugated rubber ring 122 is secured to the piston and to the short cylinder. Since the brass cylinder has been removed, the pipes, if used, as set forth above for permitting fluid flow from behind the voice coil to the sump will not be used. However, fluid may flow through the passages in outer front pole piece. Since the piston will be exposed to the surrounding medium, heat from the voice coil will be conducted to the surrounding medium through the piston.

in assembly of the various parts of the transducer, the various parts are formed, prepared by drilling apertures therethrough or threaded holes therein in their proper relationships such that they may be assembled together in their proper places. Prior to assembly of the transducer elements, the housing is first prepared by connecting the electrical connector, the cable, and terminal in place as well as the fluid valve. The magnet, pole pieces, piston, etc. are assembled together and then secured into the housing by use of the compression gasket. The soft iron back and inner front pole pieces are secured to the back and front faces of the dual diameter magnet, respectively. The charging coil is wound about the magnet in the space between the magnet and the back pole piece that surrounds the magnet and the wire ends are brought out through apertures in the back pole piece and connected to the electrical connectors secured thereto. The lead-epoxy mixture is poured into the spacing to fill the space in the area of the charging coil, and the centering ring is positioned in place in order to secure the magnet coaxially within the soft iron back pole piece.

The centering guide including the bushing, piston limit-stop, sonic resistor, and diffusion plate is secured in place onto the inner front pole piece.

The oil seal ring, compliant piston diaphragm and coil form are assembled, and the coil form is cemented to the piston. The voice coil is then wound onto the coil form and cured. The wire ends from the voice coil are connected to the electrical connectors secured onto the piston. Thus, the coil, coil wire, and piston will move together as one unit. The heat pipes, if used, may then be assembled onto the back side of the outer front pole piece. The coil-piston assembly is then secured to the back side of the outer front pole piece. The outer front pole piece is then secured to the back pole piece by bolts that pass through the back pole piece and threaded into threaded holes in the outer front pole piece. During this assembly the piston centering pin is inserted into the bushing on the front of the inner front pole piece. The electrical wire for the voice coil is passed through the aligned apertures in the back pole piece and the outer front pole piece and secured to the electrical connectors which are then secured in the apertures in the outer front pole piece. These wire conductors are long enough to connect to the supply terminal when assembled in the housing. A wire from the electrical connector in the outer front pole piece is then connected to each electrical terminal secured to the piston.

The piston cage used to limit the outer movement of the piston may be secured to the front side of the outer front pole piece. The magnet is then magnetized. The brass cylinder to which the rubber front window is attached is then connected to the front outer pole piece by sufficient bolts or screws, and filled with some appropriate liquid such as castor oil. The compression gasket and studs therethrough may then be secured in place. The compression gasket is not compressed until the magnet assembly is inserted into the housing. The four equally spaced isolation spacers may be secured to the shouder on the inner surface of the housing. The magnet unit is now ready to be placed into the housing. Thus, the assembled element is slid into the housing until the back face of the outer front pole piece contacts the isolation spacers. The protective cage is then placed over the studs through the compression gasket, nuts are placed thereon and then tightened in order to secure the assembled element into the housing by compressing the compression gasket. The wires from the voice coil may then be secured to the electrical terminal on the housing through the back open end of the housing.

Prior to assembly of the magnet into the assembled element, the magnet is not magnetized. If the magnet element is first magnetized, it would be almost impossible to assemble the various parts and insert the assembled unit into the housing. Therefore, in order to properly align the various parts during assembly, the permanent magnet is magnetized after assembly into the element. Thus, the requirement for the charging coil. While in the assembly shop, the charging coil wires are connected to a charging source, the magnet charged, and then disconnected once the magnet is permanently magnetized. A suitable handy charging source has been found to be a 24 volt D.C. battery bank which supplies 300 Amps for several seconds. The charging coil only serves to charge and discharge the magnet and is not used during operation of the device.

Subsequent to securing the element in the housing and connecting the electrical leads in place, the back plate and compensating bag are secured in place, and the desired fluid is added to the area between the magnet and the compensating bag at atmospheric pressure.

In operation, the permanent magnet sets up a magnetic field through the back and front pole pieces thereby producing a magnetic flux across the gap between the inner end of the outer front pole piece and the inner front pole piece. An A.C. voice current is applied through the voice coil to produce an alternating flux about the voice coil. The interaction between the A.C. produced magnetic flux and the permanet magnetic field causes the piston to move axially. The amount of movement is proportional to the current in the voice coil. Movement of the piston applies a force on the fluid that surrounds the piston which applies a force on the rubber front window and the surrounding water. The piston movement transmits pressure waves in the surrounding water which may be detected by suitable equipment. The front window being compliant permits large piston displacement, yet it maintains a low fundamental resonance.

The transducer may be used as a single unit or it may be assembled side-by-side with two, three or more of like units to improve the output.

Obviouly many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

l. An improved transducer element including a fluid tight housing enclosed by a compliant front window and a compliant compensating bag in the back area thereof with a magnet element fixed in the housing, between said front window and said compensating bag, the improvement comprising,

a compliant support member secured to said magnet element,

a voice coil assembly within said housing secured to said compliant support member at its rearward end for axial movement relative to said magnet elemerit,

a piston secured to the front end of said voice coil assembly,

a centering pin in combination with said piston extending along the axis operative to prevent off-axis movement of said piston and said voice coil during axial movement, and

a permanent magnet charging coil wound about a central portion of said magnet element for permanently magnetizing said magnet element subsequent to assembly into said housing.

2. An improved transducer as claimed in claim 1;

wherein,

said magnet includes an outer front pole piece with an inner front face facing the axis of said housing,

said voice coil assembled adjacent the front face of said front pole piece, and

said outer front pole piece includes apertures therethrough adjacent said voice coil to permit fluid flow to the back of said outer front pole piece and surrounding said voice coil for cooling the magnet.

Claims

1. An improved transducer element including a fluid tight housing enclosed by a compliant front window and a compliant compensating bag in the back area thereof with a magnet element fixed in the housing, between said front window and said compensating bag, the improvement comprising, a compliant support member secured to said magnet element, a voice coil assembly within said housing secured to said compliant support member at its rearward end for axial movement relative to said magnet element, a piston secured to the front end of said voice coil assembly, a centering pin in combination with said piston extending along the axis operative to prevent off-axis movement of said piston and said voice coil during axial movement, and a permanent magnet ''''charging'''' coil wound about a central portion of said magnet element for permanently magnetizing said magnet element subsequent to assembly into said housing.

2. An improved transducer as claimed in claim 1; wherein, said magnet includes an outer front pole piece with an inner front face facing the axis of said housing, said voice coil assembled adjacent the front face of said front pole piece, and said outer front pole piece includes apertures therethrough adjacent said voice coil to permit fluid flow to the back of said outer front pole piece and surrounding said voice coil for cooling the magnet.