Patent GB-1476146-A (GB)
Title: Imaging system
IPC: G01S15/89
Filed: 1974-11-04
Abstract: 1476146 Acoustic imaging systems WESTINGHOUSE ELECTRIC CORP 4 Nov 1974 [15 Nov 1973] 47574/74 Heading G1G [Also in Division C4]  For imaging a target area acoustic signals reflected from it are received on a first transducer array; the array signals are processed electrically and used to drive acoustic transmitting transducers arranged in a scaled second array geometrically similar to the first; and the acoustic signals from the transmitting transducers are received and converted to a visual display on a screen, the signal processing being such that a scaled analogue of the acoustic signal distribution reflected from the target area is displayed. In the Fig. 3 embodiment transducer array 12 receives acoustic energy emanating or reflected from target A. The transducer outputs are processed in individual channels at 14 and the processed signals drive transducers in array 12' to produce there an acoustic energy distribution which is a scaled-down replica of that at array 12. Array 121 produces at A' an acoustic image of target A, which image is converted to optical form. The image converter may comprise a mechanically scanned detector element, or an array of detector elements whose outputs are sampled, or the Fig. 8 device having a Piezo-electric layer 64, a mosaic of conductive islands 63, and an electroluminescent layer 62. The detector element signals are recorded, details given, or applied as bright-up signals to a CRT, or energize light-emitting devices. Arrays 12 and 12' have similar geometry and are flat or spherically curved. For an active pulse sonar the processing channels may be as in Fig. 10, where the array 12 signals are amplified at 80, range-gated at 81 then split into phase-quadrature components for phase detection at 83, 84. The phase detector outputs modulate a signal of frequency f 2  scaled up relative to the acoustic carrier frequency f 1 , and the modulation products are summed and amplified at 94, 95 to energize array 12' with signals whose relative phases are the inverse of those at array 12. Array 12' and the acoustic-to-optical converter are arranged at opposite ends of a liquid-filled tank having sound absorbing side-walls. The tank may be "folded" and include one or two acoustically reflecting walls, and may be of adjustable length for focusing on targets at various ranges, Figs. 23 and 24 (not shown). Shading of the array 12 signals is effected by amplification with greater gain for the central transducers than for those towards the perimeter of the array. As alternatives to the Fig. 10 processing, one component only of the phase-quadrature components is used in each channel, Fig. 13 (not shown); or the array 12 signals are frequencyconverted (without phase-detection) by extracting lower side-band signals from mixing stages to achieve the phase inversion, Fig. 4 (not shown); or the phase inversion and frequency-conversion are effected by recording the array signals on tape at one speed and playing them back, time-reversed, at at higher speed, Figs. 15 to 18 (not shown); or the array signals are subjected to individual delays related to the positions of the associated transducers in array 12 so as to simulate an acoustic lens Figs. 20 and 21 (not shown). An arrangement for determining the bearing of a sound source comprises Figs. 25 and 26, a detector array 216 supported above the sea-bed by anchors and floats 220. The detector outputs are processed as above for energizing a scaled down transducer array 216' in a shallow cylindrical volume of a liquid or solid. Receiving transducers 230-241 drive respective light sources.