Active Compensation Method for Magnetic Interference in Magnetically Shielded Room Based on Improved Linear Extended State Observer

The presence of high-amplitude and specific-frequency magnetic interference in the environment can significantly degrade the signal-to-noise ratio of magnetocardiography (MCG) signal within a magnetically shielded room (MSR), thereby severely impeding the extraction of cardiac magnetic characteristic signal and hindering accurate diagnosis of heart-related diseases. The conventional linear active disturbance rejection control (LADRC) based active magnetic compensation system exhibits limited capability to counteract such interferences, resulting in inadequate suppression effects against high-amplitude and specific-frequency magnetic disturbances in the environment. To address this issue, this article proposes an active magnetic interference compensation method (LESO-LSEF-PR) that integrates linear extended state observer (LESO), linear state error feedback (LSEF) control law, and adaptive proportional resonance (PR) control. Comparative analysis with the LADRC control approach demonstrates that LESO-LSEF-PR offers superior attenuation performance for high-amplitude and specific-frequency magnetic interferences. Experimental results show that the LESO-LSEF-PR method proposed in this article can reduce the average magnetic field noise within the 3 ~ 40 Hz range of the MSR from 93.05 to 19.85
$\mathrm { fT/\sqrt {Hz}}$
. Compared with the traditional LADRC control method, the noise suppression effect is improved by about 29.7%.