Highly Homogeneous and Low-Noise Magnetic Field Compensation Based on the High-Uniform Magnetic Field Coils With Small Coil Constant

A highly homogeneous and low-noise magnetic field is crucial for the development of devices based on optically pumped magnetometers (OPMs). However, the creation of a highly homogeneous and low-noise magnetic field in a large region remains a technical challenge. This work describes the development of a highly precise active magnetic field compensation system based on high-uniform magnetic field coils (H-UMFCs) with a small and adjustable coil constant. The H-UMFCs are designed with reference to a self-shielding coil based on the magnetic moment compensation strategy. The proportional magnification coefficient and the current scaling coefficient of the two sets of coils are optimized to obtain high uniformity in a large region. Compared with the traditional one set of planar coils, the uniformity of the Bx coils is improved by more than six times in the same region. The active magnetic field compensation system was developed based on H-UMFCs with the coil constant reduced by controlling the current ratio of the two sets of wires in one wire slot. The performance of the compensation system was verified by experimental testing. A highly homogeneous and low-noise magnetic field environment was created with a noise of less than 10 fT/√Hz @1 Hz. The design strategy is important in the application of OPMs.