Patent GB-313031-A (GB)
Title: Magnetostrictive vibrator
IPC: B06B1/08
Filed: 1928-01-03
Abstract: 313,031. Pierce, G. W. Jan. 3, 1928. Divided on 283,116, under which a Specification was laid open to inspection under Sect. 91 of the Acts, Jan. 4, 1928. Oscillating machines. - Magnetostrictive vibrators comprise a magnetic core surrounded by a coil carrying alternating or oscillatory current, and the free frequency of mechanical vibration of the core is substantially the same as the frequency of the current. In the neighbourhood of resonance, the impedance of the coil shows a critical variation enabling the vibrator to be employed as a frequency meter or as a frequency stabilizer for A.C. machines and circuits. The vibrator is also employed as the equivalent of a transformer for transferring electric energy from one circuit to another. The principle of the invention is illustrated in Fig. 1, in which a solid tubular or subdivided core 2 placed axially within the exciting coil 10 is clamped or supported at 6, 8 and is set in vibration by supplying the coil with alternating cutrent from a machine 16. The core is of nickel, nickel alloy or other material giving large magnetostrictive effects, and is of such shape, mass, and elasticity as to vibrate at a desired frequency, which may be adjusted by fixed or movable masses 4. The frequency range may extend from 100 cycles to over 100,000 cycles. The core is magnetized either permanently or by a battery current. Electric tuning of the circuit of the coil 10 may supplement the core tuning. The impedance of the coil is much less at resonance than at other frequencies, and an indication of resonance may be given by an ammeter 20, or by the emitted sound when the frequency is in the audible range. At inaudible frequencies, a click is heard in telephones in the circuit when the frequency passes through resonance. By filing down the cores, or by adding to their mass by soldering or plating, any desired frequency may be attained. The core material should have a ratio of density to elasticity which does not. vary substantially with temperature. Annealed rods of iron, nickel, and chromium alloy are suitable, or a nickel tube enclosing throughout the whole or a part of its length a body of nickelsteel, lead, type metal, &c. The core may vibrate at its fundamental or at harmonic frequencies; and if the exciting current traverses the core lengthwise torsional vibrations may be utilized. A subdivided core may be held together by an elastic binding material, or by solder or welding; and a tubular core may be slit lengthwise tc reduce eddy currents. The core may be enclosed in an evacuated envelope. The vibrator may be used for coupling two separate circuits, for example, the plate and grid circuits of a valve generator 30 as shown in Fig. 4. Variations of plate current in the coil 22 stimulate vibrations in the resonant core 2 which react on the grid coil 24 and vary the grid potential accordingly. The coils 22, 24 may be arranged in any suitable way on the cores. The valve circuit of Fig. 4 together with another form of valve generator comprising two resistancecoupled valves are described in Specification 283,116.