GB644981A - Improvements in compressional wave transmitting and receiving apparatus - Google Patents

Abstract

644,981. Subaqueous audible and like signalling-apparatus. STEVENS, A. H. (Submarine Signal Co.)..Jan. 1, 1945, No. 58. [Class 118 (ii)] [Also in Group XXXIX] A magnetostrictive transmitting and receiving device comprises a plurality of magnetostrictive tubes each capped at one end, which end serves as a radiating element, and mounted and supported in a heavy plate which is built up to be flush with the capped ends. An arrangement of this kind produces a surface which is large compared with the wavelength of the compressional wave energy received or radiated and all points on which vibrate with the same amplitude. Figs. 1 and 2 show the general construction in which a plurality of magnetostrictive tubes 13 are mounted in perforations in a heavy plate 10 which is built up to be flush with the capped ends 14 (Fig. 4) of the tubes by means of a slab of hard rubber (or similar material) 31 and a magnetizable plate 28, the whole oscillator being secured to a bearing seat 33, and may be made continuous with the skin 36 of a vessel as shown in Fig. 3. Interchange of energy between the tubes 13 and a transmitting or receiving device is effected by means of a coil 24 (Fig. 4) wound around a core 22 which is formed as an extension of a clamping plug 16, the conical shoulders of which serve to clamp the flared end 15 of the tubes in the flared portion 12 of the plate 10 when an externallythreaded nut 25 is screwed into the plate. In addition to supplying coil 24 with alternating- current of the desired frequency (for generating compressional waves) the core 22 may be magnetically polarized by supplying a direct current through the coil 24, through a separate winding or by permanently magnetizing it, further magnetization being provided by means of coils 27 clamped between the plates 10 and 28 by bolts 29. In a modification (Fig. 3) the magnetostrictive elements are formed as narrow tubes 50 each provided with a radiating cap 51 which is larger than the tube, the energy interchange coils being in this case wound outside the tubes. The tube shown in Fig. 4 may be modified as shown in Fig. 5 by cupping the inside of the cap 26 so that the parts of the cap near the periphery of the tube are stronger than the parts at the centre. This construction produces a piston-like movement of the cap and places its resonance above that of the tube without materially increasing the mass of the cap. In an alternative construction the caps may be made of hexagonal shape and grouped together as shown in Fig. 7, the plate 28 being omitted if desired. A modified arrangement in which the magnetostrictive tubes are provided with square instead of conical shoulders is described with reference to Fig. 6 (not shown). Specifications 314,891 and 405,620 are referred to.