Protective Band For Bilaminar Transducer With Slotted Spacer Ring

Abstract

An improvement in bilaminar sonar transducers which employ slotted, complt, outer spacer rings, the improvement comprising filling the slots with a plastic resin, such as epoxy resin, having a low modulus of elasticity as compared with that of the spacer ring, and banding the spacer ring with a wrapping of fiberglass tape which is impregnated with epoxy resin and cured.

Description

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

This invention relates to bilaminar sonar transducers and especially to a protective band for the compliant spacing ring of a bilaminar transducer.

Slots in the spacing ring of a bilaminar transducer are designed to provide a high radial compliance to the transducer assembly, high compliance being a necessary condition for a maximum coefficient of electromechanical coupling, minimum mechanical stress, maximum radiation resistance and maximum output power capability. These slots, however, leave thin sections of metal in the spacer ring and the thin sections of metal are subject to failure, even under low hydrostatic pressure.

STATEMENT OF OBJECTS OF THE INVENTION

Accordingly, an object of this invention is to provide the compliant spacer with protection against failure due to hydrostatic pressure while substantially maintaining the high compliance of the spacer.

This and other objects and advantages result from filling the slots in the spacer ring with a low-modulus resin and banding the spacer ring with one or more layers of tape consolidated with a resin, the overall compliance of the filling and wrapping structure being high enough not to significantly affect the performance of the flexural disc assembly but having sufficient stiffness and strength to prevent failure of the slots due to hydrostatic pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an isometric view of the crystal backing assembly for a bilaminar sonar transducer;

FIG. 2 is an isometric view of a bilaminar sonar transducer;

FIG. 3 is an isometric view of a bilaminar sonar transducer after the spacer ring has been wrapped with fiberglass tape;

FIG. 4 is a partially sectioned side view of a crystal backing assembly; and

FIG. 5 is a partially sectioned side view of an embodiment of the invention .

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the crystal backing assembly of the typical bilaminar sonar disc transducer. This component consists of an upper and a lower metallic disc 10 and 11 separated by a spacer ring 12 around the circumference of the discs which are positioned in parallel, i.e., one above the other. The material from which the discs and spacer ring are fabricated may be stainless steel, for example. The discs are welded to the spacer ring, the welds 24 being shown in FIG. 4.

The spacer ring 12 has slots 14 therein at spaced intervals and thicker segments 22 between the slots. The welding provides a zero bending moment at the edges of the metal discs and the slots provide a high degree of radial compliance. However, the slots also give thin metal areas which are subject to hydrostatic pressure failure.

To prevent this pressure failure, the slots 14 are filled with a material which has a low modulus of elasticity compared to that of the spacer ring 12. This material may, for example, be an epoxy resin. The filled slots 15 are shown in FIG. 2 which, except for the filling in the slots, illustrates a typical bilaminar disc transducer having upper and lower ceramic discs 16 and 17 affixed to the outer surfaces of the upper and lower metallic discs 10 and 11 of the crystal backing assembly (see, also, FIG. 5).

The upper and lower surfaces of each ceramic disc are coated with a thin metallic coating which comprises an electrode. The outer-surface electrodes are electrically interconnected by wire 19 and the inner surface electrodes are electrically interconnected by wire 21, and lead wires 18 and 18' are brough out as shown in FIGS. 2 and 5.

Since filling the slots 14 is not sufficient in itself to completely protect the transducer against external pressure, the spacer ring 12 is banded by wrapping one or more layers of plastic-impreganted tape around it. This band 20 may consist of fiber glass tape impregnated with a plastic resin such as that used to fill the slots 14. The resin may, for example, be the product of the Shell Chemical Corporation designated Epon 815. The fiber glass filaments span the filled slots and provide the extra strength needed to protect the unit against hydrostatic pressure. The density of the fiber glass tape and resin is still low enough that the radial compliance of the impregnated tape is at least an order of magnitude below that of the metal spacer ring.

The resin is cured by the proper heat treatment for the particular type of resin which is used.

Obviously 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.

Claims

I claim:

1. In a bilaminar sonar disc transducer having a crystal backing assembly comprising a pair of metallic discs separated by a slotted metallic peripheral spacer ring, the improvement comprising:

a filling for said slots from a material having a low modulus of elasticity compared to that of said slotted, metallic spacer ring; and

a protective band wrapped around the outside of said spacer ring, said band comprising at least one layer of tape impregnated with a plastic resin, the density of said tape and resin being sufficiently low that the radial compliance of the combination is at least an order of magnitude below that of said slotted spacer ring.

2. A transducer as in claim 1, in which said tape is fiber glass tape.

3. A transducer as in claim 1, in which said filling and said tape-impregnating materials are epoxy resins.

4. A transducer as in claim 1, in which said tape is fiber glass tape, and said filling and tape-impregnating materials are plastic resin.

5. A transducer as in claim 1, in which said tape is fiber glass tape, and said filling and tape-impregnating material are epoxy resin.