Miniature orthogonal fluxgate sensor in rotation magnetization mode: Modeling and characterization

Orthogonal fluxgates operated with a dc bias can achieve lower noise levels by suppressing Barkhausen jumps. We constructed and mathematically modeled a small orthogonal fluxgate consisting of a NiFe electroplated Cu wire, surrounded by a pick-up solenoid. A large dc current was applied through the wire to keep the core in constant saturation. This ensures that the main permeability modulation mechanism is magnetization rotation. Several output parameters were analyzed: sensitivity, noise and the perming error amplitude, all with respect to two input parameters, constant and alternating excitation field component. A good agreement between the experimental data and the theoretical model was found, with higher deviations appearing when the excitation field was not high enough to saturate the core and domain wall movement becomes relevant. Measured sensitivities were highly dependent on the excitation amplitudes, but mostly in the hundreds of V/T, and noise levels of about 0.75 nT in the 0.1-10 Hz range were found. As for the perming, the sensor zero readout can vary about 20 μT if subjected to magnetic shocks of up to 4.8 mT.