Self-adaptive loop for external-disturbance reduction in a differential measurement setup

We present a method developed to actively compensate common-mode magnetic disturbances on a multisensor device devoted to differential measurements. The system uses a field-programmable-gated-array card, and operates in conjunction with a high-sensitivity magnetometer: compensating the common mode of magnetic disturbances results in a relevant reduction of the difference-mode noise. The digital nature of the compensation system allows for the use of a numerical approach aimed at automatically adapting the feedback-loop filter response. A common-mode-disturbance attenuation exceeding 50 dB is achieved, resulting in a final improvement of the differential noise floor by a factor of 10 over the whole spectral interval of interest.