Highly Sensitive CMOS Magnetoimpedance Sensor Using Miniature Multi-Core Head Based on Amorphous Wire

We newly report a highly sensitive CMOS magnetoimpedance (MI) sensor based on a miniature multi-core head ( $\sim 2~\mathrm{mm}^{2}$ ). The miniature head consists of 13 $\mu $ m diameter amorphous wires and pick-up coils totaling 250 turns. In this paper, the sensitivity and noise level of the prototype sensor is investigated. We showed that the noise floor of the prototype sensor is lower than 100 pT/ $\mathrm{Hz}^{1/2}$ for the frequency range of 20–500 Hz. We estimated the peak-induced voltage at the pick-up coil on the basis of off-diagonal impedance theory. The results obtained in this paper will be useful for designing a highly sensitive MI sensor based on a miniature multi-core head with a CMOS pulse circuit.