Vector fitting-based full-bandwidth crosstalk suppression in triaxial optically pumped magnetometers

Optically pumped magnetometers (OPMs) in magnetoencephalography (MEG) provide ultrahigh sensitivity and spatial resolution, making them a powerful new generation of MEG sensors. Recent studies suggest that triaxial OPMs, which can characterize the complete field vector and increase the amount of signal, represent a promising advancement for MEG applications. However, triaxial OPMs face an unavoidable inter-axis crosstalk issue, which limits the advantages of triaxial OPMs in MEG applications. This study modeled and comprehensively analyzed the inter-axis crosstalk, revealing that inter-axis crosstalk exhibits distinct frequency characteristics, which have not been considered in previous research. Due to the wide frequency range of human brain activity signals, the frequency characteristics of inter-axis crosstalk make it difficult to suppress effectively in practical applications. To address this problem, we proposed a vector fitting-based full-bandwidth crosstalk suppression method in triaxial OPMs. The vector fitting algorithm was employed to identify the transfer function model of the inter-axis crosstalk and derive a frequency-dependent correction matrix to suppress the inter-axis crosstalk in full bandwidth. The inter-axis crosstalk of the triaxial OPM was suppressed to less than 0.5 % within the frequency range of DC to 600 Hz. Our study presents a highly effective inter-axis crosstalk suppression method, which successfully addresses the application challenges of MEG using triaxial OPM.