GB2112249A

GB2112249A - Acoustic underwater antenna

Info

Publication number: GB2112249A
Application number: GB08235965A
Authority: GB
Inventors: Horst Arend; Peter Mertens
Original assignee: Fried Krupp AG
Current assignee: Fried Krupp AG
Priority date: 1981-12-19
Filing date: 1982-12-17
Publication date: 1983-07-13
Also published as: AU9157982A; DE3150456C2; AU557192B2; DE3150456A1; GB2112249B

Abstract

An acoustic underwater antenna, consisting of an acoustic transducer (10) and a surrounding jacket (11), in which, for the purpose of achieving sufficient stiffness and good acoustic properties of the jacket, the transducer is supported by opposed jacket walls (19, 20) of a castable elastomer, particularly polyurethane and surrounded by cross webs (21, 22) formed integrally with the jacket. <IMAGE>

Description

SPECIFICATION Acoustic underwater antenna The invention relates to an acoustic underwater antenna of the kind set out in the preamble to claim 1.

In a known acoustic underwater antenna of this kind the jacket is made of rubber. Such a material has relatively good acoustic properties so that the sound transducer is effectively coupled to the surrounding medium, water. Owing to the low resistance of rubber to mechanical deformation a very expensive construction is necessary to obtain a sufficiently firm retaining jacket.

In another known acoustic underwater antenna of the above kind the jacket is accordingly of plastics material reinforced with glass fibres (GFK). Such a jacket can be made for low frequency underwater antennae (e.g. 10 kHz) with good acoustic performance and sufficient thickness, since it is form retaining even under high dynamic loading. This jacket is unsuitable for high frequency underwater antennae because its thickness must be reduced to a few millimetres for good acoustic performance, because otherwise it is impossible to avoid a diminution in acoustic performance of the underwater antenna because of the high damping of the jacket layer.

Accordingly, owing to the inhomogeneties in the material which readily arise in manufacture of a jacket of GFK, its acoustic properties exhibit wide regional differences. Also relatively small impact loads on the jacket, e.g. shocks or the like, which are insufficient to destroy or visibly damage the jacket can cause a so-called delamination of the material, resulting in displacement of the glass fibres within the structure and formation of air inclusions. This causes substantial loss of acoustic properties in these regions and consequent diminution of the performance of the underwater antenna.

The object of the invention is to provide an underwater antenna of the above kind in which the jacket has both good acoustic properties and stability of form.

This object is achieved by an acoustic underwater antenna of the kind set out in the preamble to claim 1, by the characteristics set out in the characterizing portion of claim 1.

The jacket of the underwater antenna according to the invention has a very good acoustic behaviour. The acoustic properties of the jacket material are, with extensive freedom from filling material, similar to those of water so that optimum coupling of the underwater antenna to the surrounding water is ensured. The jacket material, in contrast to GFK, exhibits a high degree of homogeneity so that the same acoustic achievement can be expected at each portion of the jacket. The jacket can, irrespective of the transmission frequency of the underwater antenna, be made relatively thick without marked influence on the acoustic behaviour.Despite the relatively soft nature of the material of the jacket, the manner in which the transducer is disposed in the jacket in accordance with the inventionwhereby the transducer also acts as a stiffening member for the jacket-an underwater antenna of high stiffness is provided, which can resist high dynamic loadings, such as those imposed by fast moving ships. The connecting webs provide additional transverse stiffening of the jacket and also simple fixing of the transducer within the jacket. Owing to the toughly elastic behaviour of the material, which is not affected by the connection according to the invention with the transducer, the jacket can within certain limits take impacts which would otherwise cause mechanical or acoustic damage to the underwater antenna.The underwater antenna according to the invention can be manufactured simply and in a largely automated manner, which results in relatively low production costs.

An advantageous embodiment of the invention is set out in claim 2. These measures result in a very reliable and compression resistant connection between the shell and the transducer, which ensures a high stiffness and can also be simply and cheaply effected. The casting temperature necessary for casting the jacket is far below the Curie temperature of the transducer element, so that damage to the lathe during manufacture is easily avoided.

Another advantageous embodiment of the invention is set out in claim 4. This enables the jacket to be made in response to prescribed requirements as to flow conditions in different shapes and sizes without substantial increase in use of material and without significant increase in weight. The filling of the cavities with water guarantees good acoustic coupling of the sound transducer with the surrounding medium. The cavities can be made capable of being flooded in the case of diving vessels and of being hermetically sealed in the case of surface vessels.

An advantageous method of manufacturing the underwater antenna is set out in claim 7. The complete prefabrication of the transducer including the insulating layer makes it possible to use the insulating layer as a fixing device for equidistant reception of the transducer element and to test the prefabricated sound transducer before its preferred permanent connection to the jacket. It also has the advantage that the casting of the under water antenna can be done quickly without inclusion of air in the cast mass, such as would arise in the case of rapid casting if the individual transducer elements had not been provided with a plane surface by the insulating layer. The roughening of the surface of the insulating layer ensures a seamless permanent connection between the insulating layer and the cast jacket, so that the jacket and the insulating layer form a one-piece, inseparable unit.

An advantageous form of the method is set out in claim 8. The machining of the insulating layer of the prefabricated sound transducer ensures effective removal of the parting agent adhering to the surface of the insulating layer as the result of the casing operation, so that there is no disturbance by residual parting agent to the intimate connection between the isolating layer and the jacket cast on to it.

The invention will now be further described with reference to the drawings, in which: Fig. 1 is a perspective view of an acoustic underwater antenna; and Fig. 2 is a longitudinal section along the line Il-Il in Fig. 1.

The acoustic underwater antenna consists of an acoustic transducer 10 and a surrounding jacket 11 which is hydrodynamically shaped. The sound transducer 10 consists in known manner of a cylindrical hollow carrier 1 2 of plastics material reinforced with glass fibre (GFK) on which are disposed a plurality of equally spaced transducer elements 13 (Fig. 2). Connections 14 to the transducer elements extend inwardly through holes 1 5 in the carrier 12 to internal conductors 1 6 connected to externally accessible terminals 1 7 of the transducer 10. In accordance with normal practice the vertically superposed transducer elements 1 3 are assembled in so called staves.The transducer elements 1 3 are embedded in an insulating layer 18 which covers the outer faces of the elements 1 3 for a given depth. The insulating layer 1 8 and the shell 11 are of the same material, namely a castable, toughly elastic elastomer. Preferably the material is polyurethane.

As is apparent from Fig. 1 the transducer 10 acts as a stiffening member in the transverse direction of the jacket 11, being supported by the opposite walls 1 9, 20 of the jacket and permanently attached to cross webs 21, 22 integral with the walls 19, 20. The latter is best seen in Fig. 2. The opposed walls 19, 20 and the cross webs 21, 22 bounding opposite sides of the transducer 10 are cast in substantially seamless fashion onto the insulating layer 18. The minimum width of the jacket 11 thus corresponds to the external diameter of the cylindrical transducer 1 9 and the connecting webs 21, 22 are of arcuate form.As shown in Fig. 2, the webs 21, 22 extend over the whole axial length of the transducer 10 and therefore for the full length of the jacket 11 and form with the walls 19, 20, which converge in streamline fashion at the front and rear ends of the jacket 1 two separate cavities 23, 24. The cavities serve to receive a medium, preferably water, for acoustically coupling the transducer 10 to the medium, water, surrounding the underwater acoustic antenna.

These cavities are hermetically sealed by a cover plate, not shown, attached by means of screwthreaded holes 25 in the walls 19, 20. In the case of diving vessels openings can be provided in the cover plate to permit flooding of the cavities 23, 24.

The preferred underwater antenna shown in Figs. 1 and 2 and described above is made as follows: The transducer 10, with the insulating layer 1 8 and the attached transducer elements, is first completely prefabricated, the transducer elements 13 being first fixed to the carrier 12 in their correct positions and the insulating layer 18 then being cast around this assembly. The surface of the insulating layer 18 is then machined to a given depth to remove parting agent adhering to the surfaces as the result of the casing operation.

Simultaneously with this or afterwards the surface of the machined insulating layer 18 is roughened. The transducer 10 is placed after this treatment in a mould of the precise form desired for the jacket. Cores in the mould determine the size of the cavities 23 and 24. The material of the jacket is then introduced under pressure at the bottom of the mould and the entire jacket 11 is cast in an upward direction. Finally the cores are withdrawn upwardly and the almost complete underwater antenna removed by opening the two-part mould. To complete the mould the open upper end of the jacket 11 is closed by fitting the cover plate, not shown.

The invention is not limited to the abovedescribed embodiment. Thus the insulating layer 1 8 can be formed integrally with the walls 19, 20 of the jacket and the webs 21, 22. In this case the jacket 11 and the insulating layer are cast in a single operation. It is also not essential for the transducer 10 to be cylindrical, it can have desired other forms. Also the webs 21, 22 and the walls 19, 20 on the one hand and the transducer 10 on the other hand may be separabie from one another.

Claims

1. An acoustic underwater antenna comprising an acoustic transducer and a surrounding jacket, characterised in that the jacket consists of a castable toughly elastic elastomer, preferably polyurethane, and the transducer is supported along one dimension of the jacket against opposing walls of the jacket and is surrounded by and preferably permanently connected to webs integral with and extending transversely with respect to the walls of the jacket.

2. An antenna according to claim 1, characterised in that the transducer comprises a plurality of transducer elements mounted on a carrier and embedded in an insulating layer and the opposed walls of the jacket and the transverse web on opposite sides of the transducer are cast in seamless fashion on or themselves constitute the insulating layer.

3. An antenna according to claim 2, characterised in that the insulating layer is of the same material as the jacket.

4. An antenna according to one of claims 1 to 3, characterised in that the webs extend for the full axial length of the transducer and form with the walls of the jacket two separate cavities for reception of a medium, e.g. water, for acoustically coupling the transducer to the surrounding water.

5. An antenna according to one of claims 1 to 4, characterised in that the minimum width of the jacket is substantially equal to the minimum outer dimension of the transducer.

6. An antenna according to one of claims 1 to 5, characterised in that the transducer is of substantially cylindrical form and the webs are arcuate.

7. A method of making an acoustic underwater transducer according to one of claims 2 to 6, characterised in that the transducer, including the transducer elements and the insulating layer are first completely fabricated, the surface of the insulating layer is roughened and the transducer is placed after this treatment in a mould and the material of the jacket is introduced under pressure into the bottom of the mould.

8. A method according to claim 7, characterised in that the surface of the insulating layer is subjected to at least some machining before or during the roughening.