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Quantitative measurements of direct currents are achieved by using multilayer-structure current sensor (NiFe/Cu/NiFe/Cu/Cr) carrying wide-frequency alternating currents (20 Hz-100 MHz). It was found that the impedance of the current sensor was reduced in the presence of direct currents, and decreased with increasing direct currents at medium frequency. In addition, the measurement sensitivity increased with increasing the amplitude of the alternating current. The authors also observed that the resistance variation in response to the direct currents was much larger than that of impedance and reactance at medium frequency. This current sensor was capable of measuring the direct current of at least 40 μA, exhibiting a resistance variation of 0.00674 Ω. Consequently, the ferromagnetic multilayer films may serve as a super-sensitive current sensor for the measurement of currents.

Large negative tension-impedance effect was found in a soft ferromagnetic FeCoNiBSiMo microwire, namely, the impedance of the microwire was greatly reduced by the presence of mechanical tensions at intermediate frequency. The impedance reductions could be attributed to the sharp declines of the cylindrical permeability induced by the mechanical tensions. High-frequency skin effect was decreased after stretching the microwire in the longitudinal direction, and the surface current of which redistributed due to the presence of mechanical tensions. A strong tension-resistance effect was found at high frequency, while a strong tension-inductance effect was found at low frequency. Significantly, the decreased skin effect in a stretched microwire is especially suitable for the development of high-frequency tension-impedance sensors requiring small impedance.

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