Enhancement in Sensitivity Using Multiple Harmonics for Miniature Fluxgates

The miniature fluxgates, or microfluxgates, are magnetic field sensors promising in applications of modern portable electronic devices, e.g., motion trackers and digital compasses. In comparison with the bulky traditional fluxgates, the major drawback arising from miniaturization is the reduced sensitivity and the enhanced noise level. In this work, we proposed the method to enhance the sensitivity of a miniature fluxgate by adding up the responses of four even harmonics. Numerical simulation shows that the harmonic spectrum of the induced voltage waveform consists of high-order even harmonics when the excitation current is strong enough to saturate the magnetic cores. Since the magnitude of high-order even harmonics are comparable to that of the second harmonic, it is possible to enhance the sensitivity by detecting several important harmonics. To implement the multiple-harmonic detection technique, the sensitivity and noise of a parallel-gating miniature fluxgate is investigated using the proposed method. With the reference waveform consisting of square waves at 2nd, 4th, 6th, and 8th harmonics of excitation, the sensitivity of the sensor is found to be enhanced by a factor of 2.6 in comparison with the case for a 2nd-harmonic reference alone. The field noise level is found to be reduced from 0.5 nT/√Hz to 0.2 nT/√Hz. The proposed method is promising in improving the sensitivity and reducing the field noise of a chip-scale fluxgate.