MAGNETO-IMPEDANCE ELEMENT

The magneto-impedance (MI) effect is a phenomenon in which the voltage induced by a high frequency current source in a ferromagnetic wire changes with the application of an external field. A giant MI effect was found in amorphous magnetic wires having a composition of (Fe0.06Co0.94)(72.5)Si12.5B15 and a magnetostriction of (-10(-7)). The amplitude of the wire voltage decreased by 40% at 1 MHz, 60% (600 kHz) and 50% (150 kHz), for wires having diameters 30 mu m, 50 mu m and 124 mu m, respectively, under the influence of an external longitudinal held of about 10 Oe (800 A/m). A highly sensitive and quick-response field sensor was constructed using a 200 MHz resonant multivibrator bridge-circuit combining two MI-effect elements of 1 mm length with two field effect transistors (FET). Highly sensitive flux detection was carried out by using the small MI sensor head on a rotary encoder magnet having 512 poles and a diameter of 30 mm. Discussion of a mechanism for the MI effect considers the skin effect in an amorphous wire with high circumferential anisotropy.