Influences of Extra Magnets on Giant Magnetoimpedance Effect in Amorphous Wires

Adjacent extra magnets can induce an additional impedance to an amorphous wire. We have studied the additional impedance passing through a magnetic ring and found that it is related to the electromagnetic characteristics, shapes, and locations of the extra magnet and the frequency of the ac excitation, regardless of the amorphous material properties and the extra magnetic field conditions. According to our theoretical analysis, the additional impedance severely reduces the magnetoimpedance change of the amorphous wire and destroys the giant magnetoimpedance characteristic. We therefore propose a return structure to diminish the additional impedance. Our experiments measured the impedances of an amorphous wire, a Cu wire, and the return structure with a variety of extra magnetic fields. The results confirmed the characteristics of the additional impedance and verified the effectiveness of the return structure.