US3258740A

US3258740A - Hurley etal hydrophones

Info

Publication number: US3258740A
Authority: US
Publication date: 1966-06-28
Anticipated expiration: 1983-06-28

Description

United States Patent 3,258,740 HYDROPHONES Thomas P. Hurley, Bennington, Vt., and Noel C. Sears, Becket, Mass., assiguors to Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts Filed Oct. 16, 1964, Ser. No. 404,385 2 Claims. (Cl. 340-) This is a continuation-in-part of application Serial No. 307,934, filed September 10, 1963.

This invention relates to transducers for converting electrical oscillations into traveling compressional waves in fluids and vice-versa, and in particular is concerned with transducers employing electro mechanically responsive ceramics such as barium titanate.

The principal object of the invention is to provid an underwater transducer of increased sensitivity.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following description when considered in conjunction with the accompanying drawing wherein:

FIGURE 1 is a perspective exploded view of the piezoelectric element showing the position of the contacts of the cable to the inner and outer electrodes and also showing the end caps of the present invention; and

FIGURE 2 is a perspective view of th encapsulated element.

The hydrophone of the present invention comprises a piezoelectric tube having metallic electrodes on its inner and outer surfaces. One lead of a cable is in electrical communication with the inner electrode, and at a point adjacent this connection the other lead is in electrical communication with the outer electrode. The cable circumscribes the periphery of the tube at least once, said cable being tangent to said tube at a point remote from the lead connections. Rigid, sound transparent end caps close the ends of said tube, said rig-id end caps being electrically insulated from said tube by thin gaskets. The end caps, circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, and the piezoelectric tube are encapsulated in a sound transparent elastomer.

Referring to the drawing, FIGURE 1 shows a hollowcylindrical piezoelectric element 10 having an inner 11 and outer 12 metallic electrode. The inner electrode has a bridge or passover 13. A nonelectroded area 14 separates the bridge from th outer electrode. One lead of a twin lead cable 15 is shown soldered at 16 to the bridge or passover 13, While the other lead is soldered at 17 to the outer electrode 12. Rigid, sound

transparent end caps

18 and 19, insulated by thin, sound

transparent gaskets

20 and 21 are adapted to close the ends of piezoelectric tube 10.

FIGURE 2 shows the unit of FIGURE 1 encapsulated in a sound transparent elastomer 22. This encapsulation extends along small lengths of the lead cable as shown at 23.

The use of the rigid unconnected sound transparent end caps of the present invention have been found to increase the sensitivity of the subject devices by about 3 db. It is essential that the end caps be mechnaically independent of one another, i.e. they must not be physically interconnected other than through the medium of the flexible encapsulating material. It is believed that enhancement ice of sensitivity resulting from said independently operating end caps occurs because the transducer operates as a volume element. In other words the sound pressure wave actuates the active cylindrical element both on its periphery and on its ends simultaneously. These two modes of piezoelectric activity act to reinforce each other.

The end caps can be made of practically any material which is rigid and sound transparent. Examples are rigid plastics, wood, ceramic, metal, etc., with the latter being preferred. Particularly effective end caps have been made of brass. The external surface of the end cap is preferably flat for maximum effectiveness.

The piezoelectric material can be any of the prior art materials, preferably lead titanate-zirconate or the same modified with known additives. The electrode metal can be any of the commonly used materials, e.g., silver, the platinum metals, etc. The leads may be attached to the electrodes by any means which will result in electrical communication, e.g., solder, conductive adhesive, etc. The sound transparent elastomer includes natural, reclaimed, vulcanized, synthetic rubber or polyurethanes of a Shore A durometer reading of 30 to 80.

The elastomer must also be sound transparent and preferably matched to the liquid environment in which the unit is to be used. The elastomer jacket material will act as a waterproof coating and more particularly it provides a pressure-actuated seal about th cable at the points of egress of the cable from the unit. While not essential for successful sealing it has been found that the tapered design, as shown at 23 in FIGURE 2, has greater lead flexibility which permits a smaller diameter stowage stack.

The thin, sound transparent gasket which separates the end caps from th piezoelectric tube must be a material which does not itself effect a bond between the cap and tube. It also must not bond to the encapsulating material or be wetted thereby or dissolved therein. If the gasket material possessed any of these prohibited characteristics, the end caps would actually or in effect be bonded to the transducer and the increase in sensitivity would be lost. Teflon or polytetrafiuoroethylene is an example of a gasket material possessing the required characteristics. For the purposes of this invention the term nonbonding as descriptive of the gasket means that it will not bond to the trandsucer, the end caps or the encapsulating elastomer.

In use, a plurality, i.e., two or more, of assemblies is usually employed. They are linked together by means of the cable. The bottom assembly in the string tends to be misaligned with respect to the other assembly or assemblies if a compensating weight or dummy assembly is not suspended from this bottom assembly. Therefore, it is preferred that the bottom assembly be provided with a trailing end of cable so that the compensating weight can be attached thereto.

Although the external design of the assembly has been shown to have roughly the shape of a cylinder or hockey puck, it is clear that other designs, which would be of greater advantage in the constantly moving sea, are contemplated.

As is evident from the foregoing, the invention is not to be limited to formation of the rather specific illustrative device. Modifications and variations, particularly as to shape, as well as the substitution of equivalents, may be made without departing, from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. A device of the type described comprising a piezoelectric tube having metallic electrodes on its inner and outer surfaces; one lead of a cable is in electrical communication with the inner electrode, and at a point adjacent this connection another lead is in electrical communication with the outer electrode; the cable circumscribes :the periphery of the tube at least once, said cable Fbeing tangent to said tube at a point remote from the lead connect-ions; the ends of said tube are closed by rigid, sound transparent end caps, said end caps being physically separated from the ends of the tub by thin, nonbonding, sound transparent gaskets; said tube, said circumscribing cable, including small lengths of said cable where it passes itself at the point of tangency, and said rigid end caps being encapsulated in a sound transparent elastomer.

2. The device of claim 1 wherein the end caps are metal and the gaskets are polytetrafiuoroethylene.

References Cited by the Examiner CHESTER L. JUSTUS, Primary Examiner.

G. M. FISHER, Assistant Examiner.

Claims

1. A DEVICE OF THE TYPE DESCRIBED COMPRISING A PIEZOELECTRIC TUBE HAVING METALLIC ELECTRODES ON ITS INNER AND OUTER SURFACES; ONE LEAD OF A CABLE IS IN ELECTRICAL COMMUNICATION WITH THE INNER ELECTRODE, AND AT A POINT ADJACENT THIS CONNECTION ANOTHER LEAD IS IN ELECTRICAL COMMUNICATION WITH THE OUTER ELECTRODE, THE CABLE CIRCUMSCRIBES THE PERIPHERY OF THE TUBE AT LEAST ONE, SAID CABLE BEING TANGENT TO SAID TUBE AT A POINT REMOTE FROM THE LEAD CONNECTIONS; THE ENDS OF SAID TUBE ARE CLOSED BY RIGID, SOUND TRANSPARENT END CAPS, SAID ENDS CAPS BEING PHYSICALLY SEPARATED FROM THE ENDS OF THE TUBE BY THIN, NONBONDING, SOUND TRANSPARENT GASKETS; SAID TUBE, SAID CIRCUMSCRIBING CABLE, INCLUDING SMALL LENGTHS OF SAID CABLE WHERE IT PASSES ITSELF AT THE POINT TO TANGENCY, AND SAID RIGID END CAPS BEING ENCAPSULATED IN A SOUND TRANSPARENT ELASTOMER.