GB1239124A - - Google Patents

Abstract

1,239,124. Recording sound field patterns; modulating light. BRITISH AIRCRAFT CORP. Ltd. 20 Jan., 1970 [20 Jan., 1969], No. 3160/69. Headings H4D and H4F. [Also in Division G2] Apparatus for recording a sound field pattern comprises a piezo-resistive layer 25 and an elastically deformable recording surface 13, both sandwiched between a pair of electrodes 26, 15 whereby layer 25 is responsive to sound from a source 1 to vary the intensity of an electric field between the electrodes and so cause recordable displacements of surface 13. Layer 25 may be of TiO 2 and surface 13 of plasticized P.V.C. Electrode 15 is optically transparent and supported on a glass substrate 14. A Schlieren optical system including laser 22 may be used to form a Fourier transform image of the sound field by imaging distorted surface 13 on a photographic plate 23, photochromic crystal or photo-conductor array. Electrode 26 (e.g. of aluminium and acoustically transparent) and layer 25 are supported by an acoustic-quarterwavelength (or odd multiple thereof) thick substrate comprising a bundle 27 of glasscoated copper wires which is conductive in its face-to-face direction but non-conductive in its edge-to-edge direction or (Fig. 1, not shown) by a stack of laminations, each a quarter wavelength (or odd multiple thereof) thick and presenting a progressively decreasing resistance to the sound waves and arranged on the sound source side of electrode 26 to reduce sound reflection. The apparatus may be used for underwater viewing, for detecting flaws in structures, and for medical diagnosis.