Frequency-dependent gradient error suppression method for optically pumped magnetic gradiometers

In the presence of significant common-mode noise, gradient measurement based on optically pumped magnetometers (OPMs) serves as an effective method for enhancing the signal-to-noise ratio. However, the unresolved frequency-dependent differential measurement errors will degrade the performance of gradient measurement. This work establishes a quantitative model analyzing full-band gradient differential errors based on phase-frequency response. A convenient method derived from this model enhances common-mode rejection ratio (CMRR) across the low-frequency band, which is particularly important for biomagnetic applications. By precisely controlling the magnetic fields experienced by the gradiometer, the feature point of phase intersection can be discovered, and thus the average CMRR of 1–50 Hz band is improved by more than an order of magnitude, exceeding 2000. Meanwhile, the average gradient sensitivity is also improved by 33 %. Our work provides insights for solving practical problems in OPM-based biomagnetic measurement systems.