GB402828A - Improvements in or relating to pressure wave transmitters and receivers incorporating magneto-strictive devices - Google Patents

Abstract

402,828. 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. 16472. [Class 118 (ii).] A magnetostrictive pressure wave transmitter suitable for use in echo-sounding, and subaqueous signalling systems, and for detecting underwater bodies, such as icebergs, comprises a magnetostrictive body which is so chosen, proportioned and suspended that its natural period of vibration is a harmonic, and preferably the second harmonic, of the energizing frequency. Fig. 1 shows a magnetostrictive body M suspended by rollers or resilient rubber supporting members R at points one quarter of the length of the body from each end thereof. The natural mode of longitudinal vibration of the body is indicated diagrammatically by the curve c, the body being one wave length long. The energizing frequency is made one half of the frequency corresponding to this wave length. The body M may be surrounded by separate transmitting and receiving coils L1, L2 respectively, Fig. 2, the coil L1 being tuned by the condenser C1 to the energizing frequency whilst the coil L2 is tuned to twice this frequency i.e. the frequency of vibration, by the condenser C2. The tuned circuit L2, C2 is connected between grid and cathode of an amplifying valve V, the voltage applied to this valve being limited by a pair of oppositely connected diodes D, D. A series resistance R serves to prevent short circuiting of the tuned circuit L2, 02 on transmission. If desired, the diodes can be replaced by a small spark gap, a glow discharge lamp or equivalent device. Fig. 3 shows a modification in which a single winding L is utilised both for transmitting and receiving, the winding being connected in a series loop circuit with two condensers C <1>1, and C<1>2, the latter of which is shunted by a spark gap G. In this arrangement, the energizing frequency is determined by the circuit comprising the winding L, condenser C <1>1 and spark gap G which is broken down by the relatively powerful energizing impulses. The voltages set up when receiving, however, are relatively small and are quite insufficient to break down the spark gap. The frequency to which the winding is tuned for reception is therefore determined by the two condensers C<1>1 and C<1>2 in series. According to a further arrangement, 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 polarizing fluxes, as also the energizing and /or receiving coils, may be arranged in a manner generally similar to that described in Specification 402,123. Specifications 283,116, [Class 118 (ii), Signals], and 402,829 also are referred to.