Transducer testing

Abstract: The invention concerns a method of testing a phased array of transducers in which the array is placed in contact with a block (15) of sound absorbent material surrounded by a housing (12) in such a manner that the block and housing together define an effectively anechoic chamber. A plurality of transducer elements (20) mounted within the block (15) are driven by variable phased drive electronics so as to simulate acoustic plane waves and measuring the receiver field sensitivity of the array. Alternatively, the transducers under test may be driven and the transducer elements (20) are used to measure the amplitude and phase of the acoustic wave emanating from the array under test.

Description: The present invention is concerned with the testing of phased arrays of transducers, and in particular, though not exclusively, ultrasonic transducers. Phased arrays of transducers are frequently used in underwater applications. The usual method of testing such arrays involves immersing the array into a large volume of water; typically large water tanks or open water test facilities such as reservoirs. The test facility must also provide a mechanical means of scanning the far field response of the test subject. Testing is both time-consuming, unwieldy and expansive. One method which has been proposed for overcoming the problems of testing transducers as just set out utilises accoustic loading rods which are dimensioned to simulate the acoustic impedance that a transducer would experience in actual operation. This approach also has problems when the faces of the transducers to be tested are coated in such a way that there can be no direct contact between the active face of the transducer and the loading rod. The present invention has for an object to provide a method and apparatus for testing phased arrays of transducers which alleviate the above disadvantages. According to a first aspect of the present invention there is provided a method of testing a phased array of transducers comprising: placing the array into contact with a block of material of low acoustic absorbtivity, the block being surrounded by a housing and the block and housing together defining an effectively anechoic chamber; driving a further array of transducers mounted within said block with variable phased drive electronics so as to simulate acoustic plane waves propagating towards the array under test; and measuring the receiver field sensitivity of the array under test. According to a second aspect of the present invention there is provided a method of testing a phased array of transducers comprising: placing the array into contact with a block of material of low acoustic absorbtivity, the block being surrounded by a housing and the block and housing together defining an effectively anechoic chamber; driving the array with variable phased drive electronics so as to simulate acoustic plane waves propagating away from the array through the block; and utilising a further array of transducers mounted within said block to measure the amplitude and phase of the acoustic plane waves emanating from the array under test. According to a third aspect of the present invention there is provided an apparatus for testing a phased array of transducers comprising: a block of material of low acoustic absorbtivity representing an acoustic load; a housing surrounding the block, the block and housing together defining an effectively anechoic chamber; a plurality of bi-directional transducer elements mounted within said block; and connection means for connecting said transducer elements to test equipment external to said block. EP-A-0 331 548 discloses testing the operation of a matrix of transducers. A transducer secured to one side of a block transmits into the block, in response to electrical impulses received from a generator, ultrasonic waves. The block is made of a homogeneous material transparent to ultrasound. The matrix of transducers being tested is secured to the side of the block opposite the aforementioned one side. Each transducer of the matrix produces an electrical signal representative of the amplitude of the radiation received thereby from the transducer secured to the aforementioned one side. The electrical signals produced by the matrix are processed by a processor circuit, and under the control of this circuit a display is provided on a screen of the amplitude of the radiation received by each transducer of the matrix. Thus, the screen displays the spatial distribution of the amplitude of the ultrasonic wave transmitted by the transducer secured to the aforementioned one side. In order that the present invention may be more readily understood, an embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side section through test apparatus according to the present invention, Figure 2 shows one side of the transducer array of the apparatus of Figure 1, Figure 3 shows a detail of the edge connections of the transducers of Figure 2, and Figure 4 shows a work station incorporating the apparatus of Figures 1 to 3. Referring now to Figure 1 of the drawings this shows apparatus for testing phased arrays of transducers, and particularly piezo-electric transducers mounted as a "plane" array. The apparatus shown in Figure 1 comprises a main body 10 consisting of an outer housing or casing 12 formed in two flanged parts held together by bolts. An aperture ring 11 defines a window against which, in operation of the apparatus, arrays of transducers to be tested can be placed. A detector film 14 is mounted within the housing 10 by being bonded to a block 15 of RHO-C polyurethane. A very important feature of the material of block 15 is that it has very low levels of acoustic absorption. The bulk of the remainder of the cavity of container 10 is also filled with RHO-C polyurethane as is indicated at 16. The internal walls of the cavity are potted with another polyurethane material 17 which however has a high level of acoustic absorption. As can be seen in Figure 1 the material 17 has a saw-tooth cross section in order to reduce the possibility of acoustic reflection. Because of their arrangement the interior of casing 10 effectively acts as an efficient anechoic chamber. The detector film 14 is made from a 50 um thick film of a copolymer piezo plastic. A geometric array of bi-directional transducer elements are silk screen printed onto the film 14 using silver ink. On one side of film 14 is printed a ground plane and onto the other is printed the detecting array. Active transducer areas are formed at the points of overlap between the ground plane and the detector printing. The nature of the detector array mounted on film 14 can best be appreciated from the plan view of Figure 2. In this embodiment there are 256 similar detector elements one of which is labelled 20. Conductive leads generally indicated at 21 are taken to the edge of the polyurethane block 15. The overall size of the complete array and the inter-element spacing will be chosen in accordance with the dimensions of the arrays under test and their operating frequency. However formally each element will have its major dimension substantially less than the wavelength of the array being tested. This is to ensure adequate definition although if the individual elements are too small sensitivity will be lost. Electrical connections between the bi-directional transducer elements and external test equipment are made by connectors 21 mounted on the casing 10 with the connections between the printing on film 14 and the connectors 21 being made by flexible PCB's 22. These are bonded to film 14 by conductive adhesive tape. The use of flexible PCB's and adhesive tape is to reduce acoustic reflections from the connection interface to a minimum. Figure 3 of the drawings shows the piezo-film detector and one set of PCB's more clearly. In the manufacture of the array of detectors, as has been already described, the back planes and the detector arrays are printed on either side of the film 14. In order to make the necessary outer connections one edge of a PCB 21 is secured to the appropriate side of film 14 with the respective contacts overlying. This edge is then secured by adhesive tape. The PCB is then bent so that the contacts on its opposite edge engage the appropriate contact areas on the other side of the film 14. Once again adhesive tape is used. The apparatus just described can be used either as a receiver tester or as a transmitter tester. In both modes of operation a "Near Field" measurement technique is used. An ultrasonic phased array to be tested is coupled to the input window 19 with a thin film of fluid such as a soap film. When the transducers elements 20 are used as transmitters so that the apparatus is being used to test the recurring capabilities of a phased array of transducers a signal source is simulated by arranging for a phase-shifted drive to each transducer element 20. Alternatively when used in a passive mode the array of transducer elements 20 are used to measure the amplitude and phase of the acoustic wave emanating from the array under test. A mathematical algorithm is then used to calculate the far field response of the phased array. Figure 4 of the drawings shows a complete work station incorporating the present invention. The transducer array and associated anechoic casing is mounted beneath a crosspiece 40 which can be slid up and down on pillars 41 under the control of a stepper motor 42. The crosspiece 40 carries mountings so that a transducer array to be tested can be held vertically with the active faces of the transducers to be tested facing downwardly. Such an array to be tested is indicated at 43. The work station also includes stepper controller circuitry housed at 44, a main power supply 45 and a stepper motor power supply 46. A systems monitor is shown at 47 along with a high resolution graphics monitor at 48. The work station also includes a printer 49 and keyboard 50 associated with a computer 51 having floppy and hard disc drives. One purpose of Figure 4 is to show how compact apparatus according to the present invention can be, particularly when compared with known test equipment.

Claims: A method of testing a phased array of transducers comprising: placing the array into contact with a block (15,16) of material of low acoustic absorbtivity, the block (15,16) being surrounded by a housing (12) and the block (15,16) and housing (12) together defining an effectively anechoic chamber; driving a further array of transducers (20) mounted within said block (15,16) with variable phased drive electronics so as to simulate acoustic plane waves propagating towards the array under test; and measuring the receiver field sensitivity of the array under test. A method of testing a phased array of transducers comprising: placing the array into contact with a block (15,16) of material of low acoustic absorbtivity, the block (15,16) being surrounded by a housing (12) and the block (15,16) and housing (12) together defining an effectively anechoic chamber; driving the array with variable phased drive electronics so as to simulate acoustic plane waves propagating away from the array through the block (15,16); and utilising a further array of transducers (20) mounted within said block (15,16) to measure the amplitude and phase of the acoustic plane waves emanating from the array under test. An apparatus for testing a phased array of transducers comprising: a block (15,16) of material of low acoustic absorbtivity representing an acoustic load; a housing (12) surrounding the block (15,16), the block (15,16) and housing (12) together defining an effectively anechoic chamber; a plurality of bi-directional transducer elements (20) mounted within said block (15,16); and connection means (21) for connecting said transducer elements (20) to test equipment external to said block (15,16). An apparatus as claimed in Claim 3, wherein said transducer elements (20) are mounted on a flexible film (14). An apparatus as claimed in Claim 4, wherein said flexible film (14) is a film of piezo-electric copolymer. An apparatus as claimed in Claim 5, wherein: the transducer elements (20) are formed by ground planes printed on one side of said film (14), and transducer element arrays and associated conductive tracks printed on the other side of said film (14); and said ground planes and said printed transducer elements (20) are connected to external connections by flexible PCB's (22). An apparatus as claimed in Claim 6, wherein the flexible PCB's (22) are secured to the appropriate tracks on said film by flexible adhesive tape. An apparatus as claimed in Claim 3, wherein the block (15,16) is of a polyurethane material. An apparatus as claimed in Claim 8, wherein the low acoustic absorption material of said block (15,16) is at least partially enclosed by a material (17) of high acoustic absorbtivity.

Inventors: BATEY GEOFFREY KEITH, BATEY, GEOFFREY KEITH
Applicants: GEC MARCONI AVIONICS HOLDINGS, GEC-MARCONI AVIONICS (HOLDINGS) LIMITED
Application year: 1990
Main classification: G01H3
IPC codes: G01H3