GB166769A - Improvements in or relating to subaqueous acoustic transmitters - Google Patents

Abstract

166,769. Hopwood, F. L. May 15, 1920. Subaqueous audible signals. - An underwater signal transmitter having directional properites comprises an adjustable diaphragm A, Fig. 1, vibrated by means of an electromagnet B. Both sides of the diaphragm are normally open to the water, or there may be an intervening medium which is acoustically transparent, and the device is then bi-directional. It may be rendered unidirectional by inserting an acoustically-opaque body, such as a baffle E of the kind described in S p e c ifications 139,542 and 151,920, or one or both sides of the diaphragm. In Fig. 1. the casing D, D<1> is acoustically transparent. In the form shown in Fig. 2, the electromagnet B acts directly upon an iron disc G, to which one or both of the diaphragms A, A<1> are connected, the arrangement forming in the latter case a double-diaphragm system. The degree of acoustic opacity of the chamber may be regulated by introducing various substances, such as jelly, water, &c. through plugs F'; but to ensure opacity it must not be completely filled. Baffles such as E, Fig. 1, may also be adjustably mounted outside one or both of the diaphragms A, A, in order to increase the directive effect of the transmitter.