GB402829A - Improvements in or relating to pressure wave transmitters and receivers incorporating magneto-strictive devices - Google Patents

Abstract

402,829. Subaqueous audible signalling- apparatus. MARCONI INTERNATIONAL MARINE COMMUNICATION CO., Ltd., Marconi House, Strand, and HINTON, N. P., 57, Broughton Avenue, Finchley, both in London. June 10, 1932, No. 16473. [Class 118 (ii).] A magnetostrictive pressure wave transmitter suitable for use in echo-sounding, and subaqueous signalling systems, and for detecting under-water bodies, such as icebergs, comprises a magnetostrictive body of a material, such as steel or cobalt, which exhibits for a steadily increasing magnetic field first an elongation and then a contraction or first a contraction and then an elongation, the body being so proporportioned and suspended and the energizing field being of such amplitude that said body vibrates at a triple or third harmonic frequency with respect to the energizing frequency. The figure shows a magnetostrictive body M suspended midway of its length by knife edges K and by rollers or resilient rubber supporting members R at points one sixth of the length of the body from each end thereof. The natural mode of longitudinal vibration of such a body is indicated diagrammatically by the curve c, the body being three half wave-lengths long. The energizing frequency is made one third of the frequency corresponding to this wavelength. If desired, separate windings for transmission and reception or a common winding for transmitting and receiving may be associated with the body M, the circuit arrangements being as described in Specification 402,828. Alternatively, a separate transmitter and receiver are employed, the receiver being tuned both as regards the dimensioning and method of suspension of the body and as regards the electrical circuit thereof to the harmonic frequency. The return magnetic path for the alternating and polarising fluxes, as also the energizing and/or receiving coils, may be arranged in a manner generally similar to that described in Specification 402,123. Specification 283,116, [Class 118 (ii), Signals], also is referred to.