Off-Diagonal Impedance in Amorphous Wires and Its Application to Linear Magnetic Sensors

Abstract

-Index Terms -ferromagnetic wire, magneto-impedance sensor, magneto-impedance tensor, diagonal impedance, off-diagonal impedance, antisymmetrical impedance.

Magnetoimpedance in soft magnetic amorphous and nanostructured wires

“…The magnetic permeability depends as well on the drive current frequency in a complicated way, and is also affected by the magnetic anisotropy induced by the thermal treatment. In the case of nanostructured samples, ρ changes with the thermal treatment, improving the impedance response with the nanocrystallization of the sample [25]. Therefore, in the case of high values of the drive current frequency, only the outer layer of the sample is responsible for the measured impedance, and for lower frequencies the axially magnetized inner domain would also intervene, if not all, at least some part of it.…”

“…This tensor establishes the relationship between the tangential electric field (which originates the voltage) and the tangential magnetic field (which determines the current) on the wire surface. The diagonal axis ζ zz and offdiagonal ζ φz components of the impedance tensor can be derived from the voltage V z between the wire ends for the conventional MI, or the voltage V φ of the pick-up coil, respectively [23,25]:…”

“…1 [25], and the MI rate can then be defined with respect to the magnetic saturation of the sample at the maximum applied field H max as…”

“…The off-diagonal MI effect originates in the existence of cross magnetization processes when the sample is axially magnetized and an ac current is flowing through it [22][23][24][25]. The large responses are favoured by the existence of a helical path around the direction of the excitation current [45].…”

“…This effect has shown a great potential of amorphous ferromagnetic wires, microwires and ribbons for microminiature magnetic field sensing applications. Their main advantages are the high response non hysteretic behaviour, low power consumption and very simple sensor scheme, which make them very promising materials for sensor technology [22][23][24][25].…”