GB1404029A - Magnetostrictive methods and apparatus - Google Patents

Abstract

1404029 Magnetostrictive motors INTERNATIONAL NICKEL Ltd 14 Dec 1972 [16 Dec 1971] 57836/72 Heading H2A [Also in Division H4] A magnetostrictive transducer, such as described in Specification 1,337,822, has a core of material whose Young's Modulus varies with magnetization intensity whereby the variation in the average magnetization intensity causes a change in resonant frequency of the core. A driving circuit energizes two coils to produce intersecting electromagnetic fields in the core and includes means for varying the average intensity of magnetization of the core and thus its resonant frequency. This permits varying the operating frequency (which nevertheless remains the resonant frequency) while retaining good electromechanical efficiency and linearity. The radiated frequency can be shifted for underwater purposes of encoding, identification or other communication. By varying the average intensity of a core to 1/3 and “ of saturation intensity the resonant frequency may be 15,500 Hz, 16,000 Hz and 15,000 Hz. For underwater sound communication the three different frequencies may actuate three different underwater acoustic receivers. At least one of the electromagnetic fields varies cyclically and the frequency of the cyclic variations may be varied, e.g. by using a variable frequency oscillator to supply alternate unidirectional pulses of current to the two coils. An adjustable D.C. source provides for variation of the average magnetization intensity in the core. The transducer structures may be identical with those of Specification 1,337,822. Alternatively the transducer may comprise an elongate solid magnetostrictive core 41 (Fig. 4) and orthogonal coils 42 and 43. Coil 43 is in two mutually parallel loops (see also Figs. 5, 6, not shown).