GB2180120A - Mounting transducers - Google Patents

Abstract

An array of sonic transducers (11) are mounted and located in a block of open-cell foam plastics material whose cells are filled with eg castor oil. The active faces of the transducers are located in recesses (10J) in a mould (10D) before introduction of the foam so that the active faces will be exposed and protrude from the moulded block. The array in its block is mounted in an outer casing sealed against entry of water. A space (34) within the casing and in communication with the active faces is filled with oil. <IMAGE>

Description

1 GB 2 180 120 A 1

SPECIFICATION

Mounting of sonic devices This invention relatestothe mounting ofsonicdevicesbywhichterm is meant a transducer for the transmission and/or reception of sound energy.

Particularlyfor underwater installations a number of such devices are often formed as an array and it is therefore necessary accuratelyto locate each sonic device relative to other sonic devices of the array. Hitherto such arrays have been held and located by a form of mechanical structure which generally comprises a metallic block or stave. Such a stave is gener- ally produced by machining, from the solid, the appropriate apertures for each sonic device and location means has to be provided to provide the required support, for example of a resilient nature, for each device at its nodal point, in its respective aperture in the stave, whilst mechanically de-coupling itfrom every other device. Such constructions are relatively complex in design, expensive to manufacture, and unnecessarily heavy. These considerations also introduce complexities in the mechanical structure which may impairthe acoustic performance of the elements of the array.

An object of the present invention therefore isto provideways of mounting and locating sonic devices e.g. to form an arraywithout having a complex sup- porting construction, but atthe sametime providing for optimum performance of each device once mounted and located.

According to one aspect of the present invention at least one sonic device is mounted and located in a block of foam plastics material.

According to one particular aspect of the present invention an array of sonic devices comprises a plurality of spaced sonic devices which are mounted and located with respectto one another by a block of foam plastics material. Preferablythe block of foam plastics material is formed with the sonic device, or the devices of the array, in situ during moulding of the block.

Preferably all electrical leads or other inter- connections between the individual sonic devices of the array, and/orfrom the devices to a region externaiiy of the array, are encapsulated in the block of foam plastics material.

The plasticsfoam material used fortheformation of the block mayvary according to requirements but it may specifically be BIBBITHANE ISOFOAM 510 prepared and cured in accordance with the manufacturers instructions.

According to another aspect of the present inven- tion the foam plastics material is impregnated with liquid e.g. castor oil. This feature is found to improve the mechanical decoupling of one sonic devicefrom each other device of the array, byvirtue of the oil within the foam itself, and in certain circumstances it is believed that the liquid e.g. oil provides a film around the device which improves the attenuating effect.

The oil may be introduced during or after application of vacuum to the formed foam in orderto extract as much air as possible from the foam and replace it with oil.

According to anotheraspect of the present invention a method of encapsulating an array of sonicclevices comprises locating the array of sonic devices in their required spaced relationship within a mould, introducing foam plastics material into the mould and allowing thefoam plastics material to cure in the mould. Preferablythe method includes a step of electrically connecting at least certain of the sonic dev- ices of the arraywith one another andlorthe provision of electrical leads extending externallyfrom the array priorto the encapsulation in the plasticsfoam.

In orderto provide accurate location of the individual sonic devices of the array in the resulting block of foam plastics material, parts of each sonic device are preferably provided with accurate location means in the mould priorto the introduction of the plastics foam. Such location means preferably ensures that any active faces of the sonic devices are free of plastics foam in the resulting product.

Whilst it is envisaged that in most cases an array of sonic devices will be located within a single block of foam plastics material, in certain circumstances, it may be appropriatefor each sonic deviceto be loc- ated in an individual foam plastics block, and forsuch blocksthen to be assembled into an array.

According to anotheraspect of the present invention an array of sonic devices comprises a blockor blocks of foam plastics material within cavities of which individual sonic devices are located, with operative heads of the sonic devices exposed, and the block or blocks is or are mounted in an outer casing a wall portion of which is spaced from the block or blocks in the region of the operative heads, and the space in that region is filled with a liquid.

In certain instances the liquid may be an oil, such as castor oil, and preferably the same oil is employed to impregnate the foam plastics material.

The invention may be carried into practice in a number of ways but one specific embodimentwili now be described by way of example with reference to the accompanying drawings in which:

Figure 1 diagrammatically illustrates a completed moulding tool; Figure2 is a diagrammatic sectional side elevation through the tool of Figure 1 taken on the line 2-2 of Figure3; Figure3 is a plan view of the tool of Figure 1; Figure 4 is a diagrammatic perspective view of a completed array of sonic devices produced in accordance with the present invention, Figure 5 is a transverse cross section of an array of the type shown in Figure4, assembled in an acrylic casing, and Figure 6is a longitudinal cross section of one end of the assembly of Figure 5.

Figure 1 illustrates a typical moulding tool 10 employed with the present invention and having a base 1 OA, end walls 1 OB and 1 OC, and side walls 1 OD and 1 OE, the latter having a recess 1 OF between them and a [edge 1 OG (see Figure 2) which forms the top of the mould.

As shown in the cross-section of Figure 2, within the mould a single longitudinal cavity 1 OH is formed within which an array of sonic devices 11 can be loc- 2 GB 2 180 120 A 2 ated as diagramatically shown in Figure2the array comprisingtwo longitudinal rows of spaced devices. The location of the sonic devices within the mould is accurately carried out byfirstly locatingthe devices in locating recesseslOJ of the base 10A.Thereafter, and before the remainder of the mould isassembled, appropriate wiring of the devicestakes place. Each sonicclevice iscoatedwith an appropriate releasing agentin orderto avoidthefoam plastics material stickingto it,sincethiswouid affectthe resonanceof thedevice.The endwalls and side walls are then placed in position,the latterabutting oneanother in a vertical plane 40 following which asetof holding pins 12 are projected down through the ledge 1 OG.

Each pair of pins 12 is connected to one of a series of horizontal bars 14 each of which, in turn, is connected to a pair of furthersupports 16 projecting upwardlytherefrom.

In this waythe sonic devices are accurately located and secured within the mould cavity 1 OH priorto a moulding operation, during which foam plastics material is either poured, or injected, into the cavity via one or more injecting sprues or holes 18formed in the ledge 1 OG as shown in Figure 3. Preferablythe choice of foam, e.g. BIBBiTHANE ISOFOAM 510, is such that injection, and curing can take place at room temperature. During curing, the holes 18 may be sealed. If the foam plastics require heat-curing this can be carried out in an oven. The resulting foam block 22 is shown diagrammatically in Figure 4. It provides a lightweight structure in which the array of sonic devices are effectively encapsulated, although, as shown in Figure 4,the element heads 24 of the array of devices are left exposed by the form of the mould and the method of support of the devices therein priorto moulding.

Afterthe array of Figure 4 has been produced,the block offoam plastics material is subjected to a vacuum in orderto extract as much air as possible from thefoam, priorto the introduction, either by virtue of thevacuum, orby injection methods, of an appropriate oil, e.g. castor oil.

Such impregnation produces a supportforthe arraywhich is found to provide excellent location for the sonic devices and excellent mechanical decoupling of the sonic devices from one another, and it is believed thatthe oil exists as a film around each device. The end walls 1 OB and 1 OC are preferably provided with circular recesses (not shown) so thatthe end product has integral disc-like protruberances 20.

The resultant oil-impregnated block of foam plastics material with the array of sonic devices embedded therein is now mounted in the manner shown in Figures 5 and 6 in a casing 30 of acrylic material. The casing comprises a longitudinal tube having end caps 32 of the form shown in Figure 6. Itwill be seen from Figures 5 and 6 thatthe casing 30 in the region of the heads 24 of the sonic devices is spaced from these heads, and this space is fil led with castor oi 134 being the same oil as is em ployed for the impreg nation of the foam plastics material. The choice of castor oil in this particular instance is related to the intended use of the completed array i n that it has a similar acoustic refractive index as the sea waterwithin which it is intended to operate.

The end caps 32 locate the protruberances 20 of the foam plastics material in order to provide secure location for the foamed arraywithin the casing 30. Between the end caps 32 and the tube of the casing suit- able 0-ring seals 36 are provided.

Claims (14)

1. A sonic device mounted and located in a block of foam plastics material.

2. An array of sonic devices comprising a plurality of spaced sonic devices which are located with respectto one another by being mounted in a block of foam plastics material.

3. A device or devices as claimed in Claim 1 or Claim 2 in which electrical leads or other interconnections from the device or devices are encapsulated in the block of foam plastics material.

4. A device or devices as claimed in any preced- ing claim in which the cells of the foam plastics material are impregnated with liquid.

5. A device or devices as claimed in Claim 4 in which the liquid is castor oil.

6. A device or devices as claimed in any preced- ing claim in which operative heads of the devices are exposed or protrude from the block.

7. An array of sonic devices arranged substantially as herein specifically described with referenceto Figure 4 of the accompanying drawings.

8. An array of sonic devices comprising a block or blocks of foam plastics material within cavities of which individual sonic devices are located, with operative heads of the sonic devices exposed, the block orblocks being mounted in an outercasing.

9. An arrayas claimed in Claim Sin which awall portion of the outer casing is spaced from the block or blocks in the region of the operative heads, and the space in that region is filled with a liquid.

10. An arrayasc[aimedin Claim 8orC]aim9in which the outer casing is sealed against the entry of water.

11. A method of encapsulating an array of sonic devices comprising locating the array of sonic devices in their required spaced relationship within a mould, introducing foam plastics material into the mould and allowing the foam plastics material to cure in the mould.

12. A method as claimed in Claim 11 which includes a step of electrically connecting at least one of the sonic devices of the array with another and/orthe provision of electrical leads extending externally from the array, priortothe encapsulation in the plasticsfoam.

13. A method asclaimed in Claim 11 orClaim 12 in which active faces of each sonic device are accurately located in the mould priorto the introduction of the plastics foam.

14. A method as claimed in anyof Claims 11-13 in which after foam plastics material has cured, it is subjected to evacuation of the cells andfilling of the cells with a liquid.

Printe d for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd, 1187, D8817356. Published byThe Patent Office, 25 Southampton Buildings, London,WC2AllAY, from which copies may be obtained.