High-precision suppression of spatial harmonic interference for creating an extremely weak magnetic field measurement environment

Measurement of the biomagnetic field requires an extremely weak magnetic field environment. However, the harmonic magnetic field of random frequencies generated during the operation of high-power electrical appliances will disrupt the magnetic field measurement. The traditional linear active disturbance rejection control (LADRC) has insufficient ability to suppress random frequency harmonic magnetic interference. To address this issue, this paper proposes a novel high-precision harmonic interference suppression method, in which two improvements are made to LADRC. One is to add a repetitive controller (RC) in parallel with the LADRC to enhance the harmonic disturbance suppression capability of the specific frequency. Based on the new controller (LADRC-RC), the other is to introduce a multiresonant frequency-locked loop (MSF), which can adaptively track the fundamental frequency of the harmonic magnetic interference. The experimental results demonstrate that the proposed LADRC-MSF-RC method enhances the compensation capability for spatial harmonic magnetic field disturbances by 34.37% compared to conventional methods. The proposed LADRC-MSF-RC method has better application prospects in extremely weak magnetic field measurement.