Design and implementation of driving circuits for micro fluxgate sensors employing multiple-harmonic characteristics

A study on the design and implementation of a fluxgate magnetometer´s sensing circuits based on the time-domain output waveform of a micro fluxgate sensor is presented. According to earlier studies, the frequency and amplitude of excitation voltage, and the hysteresis loop of core material are the major factors to determine the field-to-voltage transfer coefficient of the fluxgate. The fluxgate features dual-core material made of nickel-iron alloy with high permeability. The demodulation of driving circuits with feedback operation can significantly enhance the sensitivity and linear range of the sensor. The concept of the driving circuit design is the mixture of the multiple-harmonic output characteristics from the fluxgate and specific reference signals. The fluxgate´s characteristics such as sensitivity, frequency response and noise are measured. It is noted that the sensitivity and the bandwidth of the fluxgate magnetometer with feedback mode can be enhanced up to 40 V/mT and 5 kHz. Finally, a practical application to measure the magnitude of earth magnetic fields is also reported.