Crosstalk Reduction for Mz/Mx Magnetometer Array

Optically pumped magnetometer (OPM) array shows a promising future for magnetic source imaging (MSI) in the unshielded Earth’s environment, with applications in biomedical imaging and geophysical survey. However, for total-field OPMs in the Mz/Mx mode, radio frequency (RF) magnetic fields oscillating at different frequencies tend to cause crosstalk between adjacent sensors obviously. In this work, a scheme to reduce the RF magnetic field crosstalk between sensor units was investigated. First, the dependence of the Mz magnetometer sensitivity on the RF magnetic field and cell temperature was explored experimentally. To reduce the RF field, we optimized the cell temperature and set lower laser power. With the RF field set to 150 nT, the full-width at half-maximum (FWHM) of the absorption curve of magnetic resonance is 1.12 Hz under $10~\mu $ T, which gives a magnetic resolution of 20 pT. Moreover, three types of coils consisting of the square Helmholtz coils, the biplanar X coils, and the biplanar Z coils have been deeply explored in terms of their stray fields. Compared to the other two kinds of coils, the stray field of biplanar Z coils drops more rapidly in the XOY-plane and the XOZ-plane. Specifically, the minimum spacing between adjacent sensors can be reduced from 23.87 to 10.10 cm if the RF magnetic field is generated by biplanar Z coils instead of the square Helmholtz coils, with crosstalk remaining below 0.1%.