A dual-stage magnetic field compensation method inside a lightweight magnetic shielding room based on combined external and internal coils

Atomic magnetometers are magnetic field sensors that measure extremely weak magnetic field signals, and their measurement process typically requires a magnetic environment with high uniformity and low residual magnetic field. This paper proposes a dual-stage magnetic field compensation method for a lightweight magnetic shielding room (LMSR) based on a combination of external and internal coils. The first stage uses external coils to compensate for the residual magnetic distribution inside the LMSR, achieving a near-zero magnetic field level in the target area. Building on this initial compensation, the second stage employs internal coils designed with a particle swarm optimization algorithm that incorporates the distribution of the residual magnetic field to enhance the spatial magnetic field uniformity and compensate for magnetic field noise. Experimental results demonstrate that the dual-stage magnetic field compensation method designed for the LMSR effectively improves the uniformity of the target area with the central magnetic field close to 0 nT. After compensation with the external coils, the maximum values of the residual magnetic field components in three axes are decreased by factors of 2.5, 4.04, and 8.1, respectively. Following compensation by the internal coils, there is a significant improvement in the measurement performance of atomic magnetometers, with the maximum magnetic field fluctuation reduced by a factor of 12.6.