Dynamic Magnetic Field Compensation Based on Real-Time Signal Separation for Array Optically Pumped Magnetometers

Optically pumped magnetometers (OPMs) operating in the spin-exchange relaxation-free (SERF) regime achieve excellent sensitivity in environments with zero magnetic fields. Therefore, it is essential to suppress the environment's magnetic field. As the environment's magnetic field is not constant, it is necessary to compensate the magnetic field dynamically. This article presents a method of compensating the environment magnetic field dynamically for array OPMs based on real-time signal separation. The OPMs serve as the signal measurement sensors, as well as the quasi-static environment magnetic field monitoring sensors. The OPMs are placed orthogonal to each other to monitor the three components of the magnetic field. The output signals are separated and reconstructed using a fast wavelet transform. The low-frequency component is utilized to calculate the compensation current and the high-frequency component is recorded as the measurement result. This method does not require any additional sensors for magnetic field compensation, resulting in a simplified setting and low cost. The experimental results show that the method can suppress the quasi-static magnetic field fluctuations to less than one percent in real time. The magnetic field fluctuation is controlled within 10, 10, and 1 pT for the three axes. For array sensors, the effect of the magnetic field gradient can be reduced by utilizing internal coils in each OPM. The magnetic signal of a human heart is measured, which verifies the feasibility of the method for ultraweak biomagnetic field measurement.