Digital Detection and feedback Fluxgate Magnetometer

. A new full Earth's field dynamic feedback fluxgate magnetometer is described. It is based entirely on digital signal processing and digital feedback control, thereby replacing the classical second harmonic tuned analogue electronics by processor algorithms. Discrete mathematical cross-correlation routines and substantial oversampling reduce the noise to 71 pT root-mean-square in a 0.25--10 Hz bandwidth for a full Earth's field range instrument. 1. Introduction In fluxgate magnetometry the amorphous metal ring core sensors developed at the Department of Electrophysics (Nielsen et al 1995) and other high-performance sensors based on crystalline milled materials are now believed to be so stable and low noise, that in full Earth's field magnetometers the analogue electronics rather than the sensor will limit the overall performance parameters. The analogue fluxgate magnetometer traditionally uses the filtered signal at the second harmonic of the sensor core excitation frequency. ..