Fabrication of soft ferromagnetic multilayer-structure sensor for measurement of microampere direct currents

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.