GB2078958A

GB2078958A - Sonar transducer mountings

Info

Publication number: GB2078958A
Application number: GB8114418A
Authority: GB
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1980-05-21
Filing date: 1981-05-12
Publication date: 1982-01-13
Also published as: GB2078958B

Abstract

A sonar transducer array has a mounting drum 1 to which are secured twenty seven bars 2 extending lengthwise of the drum and spaced apart around its circumference. Each bar carries three sonar transducers 3 directed radially outwards of the array. The bars 2 are reduced in width between the transducers 3 so as to reduce coupling between them. Each transducer 3 comprises an aluminium forward resonator, a piezo-electric element and a steel rear resonator, the bar 2 extending intermediate the piezo-electric element and the forward resonator at a node point of the transducer. <IMAGE>

Description

SPECIFICATION Sonar transducer mountings and arrays This invention relates to arrangements for mounting sonar transducers.

The invention is more particularly concerned with arrangements for mounting a plurality of sonar transducer elements together in an array.

In conventional sonar transducer arrays, transducer elements are mounted in recesses formed around the curved surface of a disc-shaped metal block such that sonar energy is propagated outwardly of the block. Several blocks are mounted axially, one above the other, to form the complete array which is contained within a fluid-tight housing substantially transparent to acoustic energy. The array and housing might be mounted on the hull of a boat, beneath the waterline, for use with standard sonar equipment in the detection of fish.

The mounting arrangements for conventional arrays are relatively heavy and, because they require to be fabricated or machined accurately from a solid block of metal, or casting, they are expensive to make.

It is an object of the present invention to provide a sonar transducer mounting arrangement that can be used to alleviate the above-mentioned disadvantages.

According to one aspect of the present invention, there is provided an electro-acoustic sonar transducer array having a plurality of electro-acoustic transducer elements arranged to propagate acoustic energy outwardly of the array, wherein each element includes two resonator portions and electro-acoustic oscillator means mounted intermediate said resonator portions, wherein said array includes plurality of elongate members mounted to extend along the length of the array, and wherein said elements are mounted on said elongate members with said elongate members intermediate the two resonator portions of each said element.

The weight and cost of making an elongate member such as a bar or strip can be considerably less than that of a solid disc-shape metal block with recesses machined around its curved surface. For this reason the weight and cost of the array can be kept to a minimum.

Some at least of said elongate members may each support a plurality of transducer elements, the said elongate member having regions of reduced width away from said transducer elements so as thereby to reduce mutual coupling of said elements.

The transducer elements may be supported by said elongate member substantially at a node point along the length of the transducer element with the elongate member intermediate said oscillator means and a said resonator portion.

The oscillator means may include a piezo-electric crystal, the resonator portions being metal blocks adapted to resonate at a selected frequency.

A sonar transducer array in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partly cut-away elevation side view of the array; Figure 2 is a view from the right hand end of the array of Figure 1 along the arrow II; Figure 3 shows a part of the array of Figure 1; and Figure 4 is a cross-sectional elevation to an increased scale of another part of the array of Figure 1.

With reference to Figures 1 and 2, the sonar transducer array comprises a central mounting drum 1 around which are mounted twenty seven mounting bars 2, each carrying three transducer elements 3.

The mounting drum 1 is an aluminium alloy casting with a hollow cylindrical hub 10 that has an open side 11 extending about halfway along it from the right-hand end 12. Annular flanges 13 and 14 extend radially from the hub 10 at both ends, the left-hand flange 14 being substantially circular and the right-hand flange 13 being partly cut-away such as to be of generally U-shape (Figure 2). The outer edges 15 and 16 of both flanges 13 and 14 are formed with a series of twenty seven flats 17 spaced around 280 , each of which has a centrally positioned tapped hole 18. The drum 1 is also provided with a mounting flange 19 that projects radially from the hub 10 intermediate the end flanges 13 and 14.

The mounting flange 19 is provided with various bolt holes 20 for use in mounting the drum 1 with, for example, the hull of a ship (not shown).

With reference now also to Figure 3, the mounting bars 2 extend between the two end flanges 13 and 14 parallel to the axis of the drum 1, each bar 2 having a hole 21 at both ends for receiving bolts 22 that are screwed into the holes 18 in the flanges. The bars 2 are of 2 mm thick aluminium alloy and may be simply formed by stamping from a flat sheet of material. The bars 2 are of a generally rectangular shape, being provided with three plate portions 23 that are separated from one another by waisted portions 24 of reduced width. The plate portions 23 are located closer to one end of the bar 2 than the other end, the bars 2 being mounted on the drum 1 in an alternate, reversed fashion such that the plate portions 23 of one bar are aligned with the waisted portions 24 of the adjacent bars.The plate portions 23 are flat and free from surface imperfections and are formed with centrally-located apertures 25 for use in mounting the transducer elements 3.

With reference now to Figure 4, the transducer elements 3 are of the electro-acoustic form having two barium titanate, piezo-electric ceramic crystals 31 and 32 sandwiched between head and tail tuned resonators 33 and 34. Each transducer element 3 is secured on its mounting bar 2 by means of a threaded stud 35 and nut 36. The stud 35 extends axially through the tail resonator 34, the crystals 31 and 32, and the aperture 25 in the bar 2, and screws into a tapped hole 37 in the head resonator 33. The head resonator 33 is 12.7 mm long and is of an aluminium alloy having a cylindrical forward section 39 of 24.69 mm diameter that tapers rearwardly at an angle 0 of 32 08' to a reduced diameter (of 13.80 mm), thereby forming a frusto-conical section 40.

The head resonator 33 is held tightly with the plate portion 23 of the bar 2, being separated from it by means of a monel gauze shim 50. A similar shim 51 is sandwiched between the other side of the plate portion 23 and the front surface of the forward crystal 32.

The crystals 31 and 32 are both of annular form having an outer diameter of 13.8 mm, a bore 7.00 mm in diameter, and being 2.32 mm thick. The crystals 31 and 32 are arranged to oscillate axially such that radiation is propagated along the length of each element 3 and radially outwards of the mounting drum 1. An electrically-insulative sleeve 52 is fitted in the bore of the two crystals to embrace the stud. The two crystals 31 and 32 are separated from one another by a brass shim 53, which serves as an electrode, and two monel gauze shims 54 positioned on opposite sides of the brass shim. Another monel gauze shim 55 separates the rear crystal 31 from the tail resonator 34.

The tail resonator 34 comprises a cylindrical block of stainless steel 14.2 mm long and 13.8 mm in diameter provided with a 4 mm deep circular recess 47 in its rear face 48 which receives the nut 36.

Before assembling the elements 3 with the bars 2, all contacting surfaces of the components of the transducer element are coated with an epoxy adhesive which sets hard to produce secure joints.

The greater effective surface area provided by the flat front face of the head resonator compared with the rear face of the tail resonator gives a greater proportion of energy in the forward, outward direction.

The shape, size and material of the head resonator 33 and the tail resonator 34 are chosen so that both will resonate at the same fundamental frequency as that at which the oscillating element formed by the crystals 31 and 32 is driven, namely 55kHz.

The position of the mounting bar 2 along the length of the transducer element 3 is such thatthe bar is at a node point in the vibration of the element so as thereby to ensure that as little vibration as possible is transmitted to the bar. The waisted portions 23 of the bar 2 further ensure that mutual coupling between adjacent transducer elements 3 on the same bar is maintained at a minimum.

By mounting the transducer elements on bars, in the way described above, the overall weight and cost of the transducer array can be kept to a minimum, and servicing is also facilitated.

It will be appreciated that the transducer element could take various different forms, shapes and sizes according to the application to which it is being put The mounting bar need not necessarily be sandwiched between the oscillator means (that is, the crystals 31 and 32) and the forward resonator but could be sandwiched between the two crystals, or between a crystal and the rear resonator, the resonators being suitably tuned such that the bar 2 is located at a node point.

Claims

1. An electro-acoustic sonar transducer array having a plurality of electro-acoustic transducer elements arranged to propagate acoustic energy outwardly of the array, wherein each said element includes two resonator portions and electro-acoustic oscillator means mounted intermediate said resonator portions, wherein said array includes a plurality of elongate members mounted to extend along the length of the array, and wherein said elements are mounted on said elongate members with said elongate member intermediate the two resonator portions of each said element.

2. An array according to Claim 1, wherein said array has a central mounting drum to which opposite ends of said elongate members are secured.

3. An array according to Claim 1 or 2, wherein said elonglate members are bars of a generally rectangular section.

4. An array according to any one of the preceding claims, wherein some at least of said elongate members each support a plurality of transducer elements.

5. An array according to any one of the preceding claims, wherein the said elongate members are of reduced width away from said transducer ele menus such as to reduce mutual coupling of said elements.

6. An array according to any one of the preceding claims, wherein said transducer elements are supported by said elongate members substantially at a node point along the length of the transducer elements.

7. An array according to any one of the preceding claims, wherein said transducer elements are mounted on said elongate members with said elongate members intermediate said oscillator means and a said resonator portion.

8. An array according to any one of the preceding claims, wherein said oscillator means includes a piezo-electric crystal.

9. An array according to any one of the preceding claims, wherein said resonator portions are metal blocks adapted to resonate at a selected frequency.

10. An array according to any one of the preceding claims, wherein said transducer elements are secured to said elongate elements by clamping together said resonator portions.

11. An electro-acoustic sonar transducer array substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.