Improvements relating to the emission and reception of submarine waves

Abstract

Abstract 145,691. Langevin, P. Sept. 17, 1918, [Convention date]. Signalling proximity of vessels, land, shoals. rocks, and icebergs; subaqueous signals.-A transmitter or receiver of high-frequency (ultra-audible) vibrations, particularly for use in directive subaqueous signalling or for detecting submarines, icebergs, or other echo-reflecting objects as described in Specification 125,122, utilizes the piezoelectric effect of quartz crystal. In simple form, the device comprises a plate of quartz having its faces cut perpendicular to the binary axis and provided with metallic coatings to form a condenser, the crystal constituting the dielectric. Pressure variations due to the received vibrations give rise to corresponding potential-difference variations between the two faces of the crystal, and these can be detected in a circuit connecting the two coatings, as, for example, by heterodyne methods used in wireless signalling. Conversely, when the faces of the crystal are subjected to potential-difference variations from a source having the desired frequency, corresponding vibrations are emitted by the device. Fig. 2 shows a form for submarine use in which a watertight casing e is closed bv a diaphragm f of mica to which a mosaic of quartz crystals a<1> a<2> is cemented. The water in which the device is immersed constitutes one plate of the condenser, a metal plate b secured to the crystals forming the other. The device is resonant to the frequency for which the combined thichness of the crystals and attached plates forms a " half-wave plate." Fig. 3 shows a form in which a thin layer of crystals a is placed between two metal plates g, g<1> of equal thickness, the resonance being secured by suitably choosing the thickness of the metal plates. The casing may contain air, in which case vibrations are transmitted only from one face of the crystals, or may be filled with insulating-liquid, when both faces of the crystals transmit.

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