Elimination of the AC modulation mutual interference for array optically pumped magnetometers

The optically pumped magnetometer (OPM) is one of the most sensitive magnetic field sensors, which is widely used for ultra-weak magnetic field measurement. To localize and quantify the magnetic source, array OPMs are needed to work simultaneously in a small area. As an OPM typically employs a modulation magnetic field, in the presence of multiple sensors, the modulation fields of the OPMs interference with each other, resulting in reduced measurement accuracy and sensitivity. This paper proposes a novel array OPMs setting to eliminate the mutual interference of the modulation magnetic field. The OPMs in the array are modulated simultaneously by a group of coils, which are optimized based on the numerical calculation to generate an almost uniform magnetic field in the sensor areas. The operating principle of the method is analyzed by solving the Bloch equation. Then, the feasibility of the method is demonstrated experimentally with compact OPMs that measure the magnetocardiography signal of human body.