I. Introduction
The GMI effect consists of a significant change in the impedance of a piece of soft magnetic material driven by a high frequency current when it is introduced into a static magnetic field [1]. The magnitude of the effect is very large in amorphous magnetic wires, either obtained by in rotating water quenching or glass-coating technique [2], [3]. In glass-covered microwires, the GMI effect depends on the ratio of the metallic inner core to the total diameter of the microwire [4]. From a large number of experiments, we have observed that the magnitude of the GMI effect is strongly dependent on the diameter of the metallic core, and subsequently, on the glass cover thickness.