AU1249192A

AU1249192A - Apparatus for testing a phased array of transducers

Info

Publication number: AU1249192A
Application number: AU12491/92A
Authority: AU
Inventors: Robert Gentles
Original assignee: GEC Ferranti Defence Systems Ltd
Current assignee: Leonardo UK Ltd
Priority date: 1991-02-20
Filing date: 1992-02-20
Publication date: 1992-09-15
Also published as: GB9103531D0; GB9203695D0; GB2253055A; WO1992015027A1; EP0525155A1

Description

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Apparatus for testing a phased array of transducers

This Invention relates to apparatus for testing a phased array of transducers.

A phased array of transducers 1s one which In a transmit mode of operation transmits acoustic plane waves in a direction determined by electrical signals supplied to the array, and which in a receive mode of operation produces electrical signals representing the direction from which acoustic plane waves are received by the array.

More particularly, the invention relates to apparatus for testing the transmit and/or receive modes of operation of an elongate phased array of transducers.

An example of an elongate phased array 1s an array commonly termed a linear towed array which 1s a one-dimensional array towed underwater. Linear towed arrays are usually tested in the environment in which they are Intended to operate, that is in the

4 open water, such as at sea or In a reservoir. However, this is inconvenient. It is more convenient to test on dry land. However, known testing on dry land does not include testing the directional sensitivity of the array.

It is an object of the present invention to provide an apparatus suitable for testing a linear towed array on dry land, which testing includes testing the directional sensitivity of the array.

According to the present invention there 1s provided an apparatus for testing the transmit and/or receive modes of operation of an elongate phased array of transducers comprising: transducer means which extends along the length of the array when the array 1s disposed for testing by said apparatus, in testing the transmit mode of operation said transducer means receiving acoustic plane waves transmitted by the array, in testing the receive mode of operation said transducer means transmitting acoustic plane waves to the array; and an acoustic coupling medium which extends along the length of the array between the array and transducer means to acoustically couple the array and transducer means, in use said apparatus functioning as a waveguide to guide said acoustic plane waves between the array and transducer means through said coupling medium.

An apparatus in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawing which Is a diagrammatic sectioned perspective view of the apparatus.

The apparatus is for testing the transmit and receive modes of operation of a linear towed array over a range of directions of transmission and reception.

Referring to the drawing, the apparatus comprises a containment vessel in the form of a channel 1 U-shaped in cross-section, a plurality of hydrophones 3, an acoustic coupling medium 5, and an acoustic absorber 7. The vertical side walls 9 of the channel 1 are spaced apart by a distance known to be less than one half the minimum wavelength of operation of the array to be tested. The inner surfaces of the side walls 9 are acoustically reflective. The hydrophones 3 are spaced at equal intervals along the length of the channel 1 approximately midway up the height of the channel 1. The hydrophones 3 are embedded within the coupling medium 5 which extends along the channel 1 and from just below the height of the hydrophones 3 to just below the height of the mouth of the channel 1. The acoustic absorber 7 extends along the channel 1 and from the bottom of the coupling medium 5 to the base of the channel 1.

In use of the apparatus, the linear towed array 11 to be tested 1s positioned as shown in the coupling medium 5 at the mouth of the channel 1 so as to extend along the length of the channel 1. The coupling medium 5 serves to acoustically couple the array 11 and hydrophones 3.

In testing the transmit mode of operation of the array 11, electrical signals provided by variable phase drive electronics (not shown) are supplied to the array 11 to instruct it to transmit acoustic plane waves in a first direction of the aforementioned range of directions to the plurality of hydrophones 3. By virtue of the spacing between the walls 9 of the channel 1 and the reflective Inner surfaces of the walls 9, the walls 9 function as a waveguide to guide the acoustic waves transmitted by the array 11 through the coupling medium 5 to the plurality of hydrophones 3. The hydrophones 3 produce 1n response to receipt of the acoustic waves electrical signals representing the direction from which the acoustic waves were received. If this direction is the aforementioned first direction the array 11 is operating properly as regards transmission 1n this first direction. The above procedure is repeated for transmission in the remaining directions of the range.

In testing the receive mode of operation of the array 11, electrical signals provided by variable phase drive electronics (not shown) are supplied to the hydrophones 3 to cause them to transmit acoustic plane waves in a first direction of the range of directions to the array 11. As in testing the transmit mode of operation, the walls 9 of the channel 1 function as a waveguide, they guide the acoustic waves transmitted by the hydrophones 3 through the coupling medium 5 to the array 11. The array 11 produces in response to receipt of the acoustic waves electrical signals representing the direction from which the acoustic waves were received. If these signals represent the first direction the array 11 is operating properly as regards reception from this first direction. The above procedure 1s repeated for reception from the remaining directions of the range.

The width of the channel 1 is less than one half the minimum wavelength of operation of the array 11 so that the channel 1 functions as a waveguide, that 1s so that the dominant mode of waveguide transmission is longitudinal between the array 11 and hydrophones 3. If It were required to test the operation of the array 11 at only one known frequency, the width of the channel 1 could either be less than one half the wavelength corresponding to this frequency or greater than this but equal to an interger multiple of this half wavelength. The channel 1 would function as a waveguide in either case. Since transmission of the acoustic waves is through the coupling medium 5 the wavelength corresponding to any frequency equals the velocity of sound in the medium 5 divided by the frequency.

The acoustic impedance of the coupling medium 5 is suitably such that the acoustic loading on the array 11 in the apparatus is approximately equal to that on the array 11 in open water. In cases where this is not so, such 1s taken into account when analysing the test signals produced by the apparatus. Water is a suitable coupling medium 5. There are other suitable coupling media 5, including solid ones. Rho-c polyurethane is an example of a suitable solid coupling medium which has an acoustic impedance close to that of water.

The acoustic absorber 7 reduces unwanted reflection of acoustlc waves from the base of the channel 1. In this connection such reflection would not occur in operation of the array 11 in open water. The acoustic absorber 7 could be dispensed with if pulsed rather than continuous stimulation testing of the array 11 were used.

It is to be appreciated that in the apparatus described above by way of example, if the coupling medium 5 were to be made of a solid material, the channel 1 could be dispensed with, the coupling medium 5 functioning as a waveguide by virtue of reflection at the air/coupling medium 5 interface at the side walls of the medium 5.

It is also to be appreciated that in the apparatus described above by way of example, if the coupling medium 5 were to be a liquid, the channel 1 could be dispensed with by arranging for the acoustic absorber 7 to extend at the sides of the medium 5 as well as at the base thereby to contain the liquid. The medium 5 would function as a waveguide by virtue of reflection at the medium 5/acoustic absorber interface at the side walls of the medium 5, although the medium 5 would be a very lossy waveguide. The overall cost of the apparatus would also rise as a consequence of the Increased use of acoustic absorber.

Claims

CLAIHS

1. An apparatus for testing the transmit and/or receive modes of operation of an elongate phased array of transducers comprising: transducer means which extends along the length of the array when the array is disposed for testing by said apparatus, in testing the transmit mode of operation said transducer means receiving acoustic plane waves transmitted by the array, in testing the receive mode of operation said transducer means transmitting acoustic plane waves to the array; and an acoustic coupling medium which extends along the length of the array between the array and transducer means to acoustically couple the array and transducer means, in use said apparatus functioning as a waveguide to guide said acoustic plane waves between the array and transducer means through said coupling medium.

2. An apparatus according to Claim 1 wherein in testing the transmit mode of operation: electrical signals are supplied to the array to instruct it to transmit acoustic plane waves in a defined direction; and said transducer means produces in response to receipt of these waves electrical signals representing the direction from which the waves were received, analysis of these electrical signals determining whether the waves were transmitted by the array in the defined direction.

3. An apparatus according to Claim 1 or Claim 2 wherein in testing the receive mode of operation: electrical signals are supplied to said transducer means to cause it to transmit acoustic plane waves in a defined direction; and said array produces in response to receipt of these waves electrical signals representing the direction from which the waves were received, analysis of these electrical signals determining whether they represent the defined direction in which the waves were transmitted by the transducer means.

4. An apparatus according to Claim 1 or Claim 2 or Claim 3 further comprising a channel in which the array, transducer means and coupling medium are disposed so as to extend therealong, said channel having walls the inner surfaces of which are acoustically reflective, reflection of the acoustic plane waves at these surfaces facilitating the functioning of the apparatus as a waveguide.

5. An apparatus according to Claim 4 wherein said channel is U-shaped in cross-section and said apparatus further comprises an acoustic absorber located in said U-shaped channel so as to extend along the base thereof, the upstanding walls of said U-shaped channel being the walls the inner surfaces of which are acoustically reflective, said array being positoned at the mouth of said U-shaped channel, said transducer means being located between said array and said acoustic absorber.

6. An apparatus according to Claim 5 wherein the width of said U-shaped channel is less than one half the minimum wavelength of operation of the array.

7. An apparatus according to any one of the preceding claims wherein said transducer means comprises a plurality of hydrophones spaced at equal intervals along the length of the array.

8. An apparatus according to any one of the preceding claims for testing a linear towed array.

9. An apparatus for testing the transmit and/or receive modes of operation of an elongate phased array of transducers substantially as hereinbefore described with reference to the accompanying drawing.