Multicore Off-Diagonal Magnetoimpedance Sensors Utilising Amorphous Wires

Abstract

Magnetoimpedance (MI) sensors are attractive for realising a localised detection of weak magnetic fields owing to micro-size and high sensitivity of the MI elements based on Co-rich amorphous wires of diameter 10-30 microns. The MI sensors in off-diagonal configuration when the signal is taken from the coil mounted on the wire have a number of advantages including linearity, enhanced output voltage, and resonance detection circuitry. In this work, the off-diagonal impedance of a number of Co-rich glass-coated amorphous wires placed in the same coil is investigated. The wires are connected in parallel and excited by a harmonic current with optimised dc bias which is used to remove the domain structure. The best sensitivity of about 350mV/Oe is obtained for two closely spaced wires at the excitation frequency of 20MHz which corresponds to the resonance conditions for the detection circuit having only 55 turns. The full scale and linearity range are also increased almost twice in comparison with those when only one wire is used. The response drops if the distance between the wires is increased which is due to a strong effect of the magnetostatic interaction between the wires. We conclude that the off-diagonal MI sensors with multiple wires can provide higher transfer function per one turn and could be advantageous for localised field detection.