Journal of the Magnetics Society of Japan

This paper describes a three–phase electric current sensor using a magneto–impedance (MI) sensor, which provides compact size and wide–range current sensing. The MI sensor is composed of a thin–film MI element and a bias coil. The MI sensors and electric current bars are placed in u–shaped cores to prevent an unwanted magnetic field from being generated by another phase current. To realize a high shielding performance and a compact size, a double shielding structure is employed. Two kinds of alternate bias are used in the system to implement a wide measurement range of 1:600. The sensor is intermittently driven by discrete sampling to realize a low power consumption of 20 mW. The influence of temperature on the MI sensor is alleviated by supplying an optimum carrier electric current. As a result, a temperature fluctuation ratio of less than ± 1.3% at -25 to 60°C was obtained.

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Magneto–impedance appears at remarkably high levels in amorphous alloys, and is used in high–sensitivity magneto–sensors made from these materials. It can also be used in non–destructive sensing systems, because it is strongly dependent on magnetic anisotropy. We therefore developed an electromagnetic ac impedance wave method (EMIW) that measures the magneto–impedance of ferromagnetism without contact. The effect of applied stress on the impedance waves of steel and nickel, under plastic deformation, was measured by EMIW, and the impedance waves were measured while decreasing the applied stress after plastic deformation. During the plastic deformation process, the applied stress effect of SM490A could be measured, but in nickel samples the changes in the impedance waves declined with decreasing stress. It was also found that the effect of applied stress on the impedance waves was different in loading and unloading.

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