Low-cost Micro Search-Coil Magnetic Sensor with Self Calibration for the Internet of Things

In this paper, a low-cost search-coil magnetic field sensor (SCMS) with an integrated self-calibration is presented. The sensor consists of a pair of micro coils (a sensing coil and a coil for self-calibration). A theoretical model and FEM model were developed for SCMS's systematic design analysis with different key parameters. We found that the normalized SNR as a function of track width $w_{c}$ has two operation regimes: noise dominant and sensitivity dominant and the existence of the critical track width ( $w_{c}$ ) ranging from $50 \mu\mathrm{m}$ to $100\ \mu\mathrm{m}$ to achieve optimal SNR. The optimized micro SCMS, with the calculated noise equivalent magnetic induction of 250nT/Hz 0.5 and the dynamic range of ±26mT at 50 Hz with amplification gain of 100 and ±5 V power supply, is successfully fabricated and tested using a low-cost four-layer Printed Circuit Board (PCB). There is a good agreement among the theoretical predictions, FEM simulations, and experimental results. The low-cost micro SCMS is promising for energy monitoring of large-scale data centers in the era of the Internet of Things.