Giant Magnetoimpedance Sensors
نویسندگان
چکیده
Magnetoinductive e ects in ferromagnetic conductors can be used for various sensors. Although the principle has been known for a long time, the usefulness of these e ects for practical applications was recognized recently, and intensive investigations began. Magnetoinductive e ects are related to magnetization of a magnetic conductor (wire, strip, thin lm, etc.) by a magnetic eld, which is produced by an electric current passing through the conductor itself. lf the current is varying with time, the magnetic ux in the conductor also varies and induces the electromotive force, which is superimposed to the ohmic voltage between its ends. For instance, in a wire with a circular cross section, the circumferential magnetic eld H induced by a constant current with the density j is H = jr=2, where r is the distance from the wire axis. For a wire of diameter 1 mm and the current density of 106 A/m , which is low enough so as not to greatly increase the temperature by joule heating, the maximum magnitude of a magnetic eld on the wire surface is 250 A/m. To get suÆciently high magnetoinductive voltage, which can be easily detected on the ohmic background signal, the circumferential reversal of the conductor magnetization must take place in magnetic elds of this order or lower. Therefore, good soft magnetic metals with high circumferential permeability are required for such applications.
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