  We present a system for active noise control (ANC) of environmental magnetic
fields based on a Filtered-x Least Mean Squares (FxLMS) algorithm. The system
consists of a sensor that detects the ambient field noise and an error sensor
that measures the signal of interest contaminated with the noise. These signals
are fed to an adaptive algorithm that constructs a physical anti-noise signal
cancelling the local magnetic field noise. The proposed system achieves a
maximum of 35 dB root-mean-square (RMS) noise suppression in the DC-1 kHz band
and 50 dB and 40 dB amplitude suppression of 50 Hz and 150 Hz AC line noise
respectively for all three axial directions of the magnetic vector field.
