Mechanism of asymmetrical magnetoimpedance in amorphous wires

Two approaches for obtaining asymmetrical magnetoimpedance (MI) characteristics in Co-based negative magnetostrictive amorphous wires are analyzed in terms of the surface impedance tensor <(zeta)over cap>, which is expressed in the form of orthogonal expansions in Bessel functions in a general case of a helical magnetization. The asymmetry in MI behavior with respect to an axial dc magnetic field can be related to either a certain asymmetric arrangement of the dc magnetic configuration or a contribution to the wire voltage due to the ac cross-magnetization process (represented by the off-diagonal component of <(zeta)over cap>). The first case is realized in a wire having a helical anisotropy and subjected to an ac current superposed with a dc current. In the other approach, the asymmetric voltage response can be obtained by applying the ac current in series through the wire and the coil mounted on it. No helical anisotropy is required in this case. These kinds of asymmetrical MI are especially important for developing autobiased linear MI sensors. (C) 1999 American Institute of Physics. [S0021-8979(99)77308-1].