Odd-Harmonic Characteristics of the Field-Modulated GMR Magnetometer

Responsivity and field noise of a bridge-type GMR magnetometer modulated by a sinusoidal alternating magnetic field were investigated in this work. The odd harmonics of output voltage were found to be more sensitive to external dc fields in comparison with the even harmonics. By detecting the field-modulated output with a reference square wave at the 1st, 3rd, or 5th harmonic of modulation frequency, the sensor responses to external fields are bipolar, non-hysteretic, and quite linear with proper modulation amplitudes. The minimum field noises were 5, 2.5, and 5 nT/√Hz at 1 Hz for the 1st, 3rd, and 5th harmonics, respectively, with power consumption less than 10 mW. The proposed operation method is promising for application to electronic compasses.