Fast Error Calibration for Three-Axis SQUID Magnetometers Based on Full-Space Rotational and Frequency-Controllable Magnetic Field

In order to overcome the limitations of the traditional error calibration method for three-axis superconducting quantum interference device (SQUID) magnetometers, this article presents a fast error calibration method for three-axis SQUID magnetometers. In the proposed method, a full-space rotational and frequency-controllable magnetic field with constant total field intensity can be generated by a triaxial Helmholtz coil. Meanwhile, the nonorthogonal error, zero offset error, and proportional coefficient error of the three-axis SQUID magnetometers, which measure the relative value rather than the absolute value, can be accurately solved by an error modeling and ellipsoid fitting theory. Compared with the traditional scalar calibration method, this method replaces the rotation of Dewar and three-axis SQUID magnetometers with a rotating magnetic field, thus avoiding the interference and influence of motion. Compared with the traditional vector calibration method, this method does not need to ensure the alignment between the three-axis SQUID magnetometers and triaxial Helmholtz coil. Moreover, the interference of low-frequency magnetic field can be suppressed by shortening the period of rotating magnetic field. Simulation and experiments prove the effectiveness of this method. After calibration by the proposed method, the root-mean-square error is reduced to 0.414 from 138.411 nT in the electromagnetic shielding room. Repetitive and comparative experiments with the traditional method in field also prove the superiority and stability of the proposed method.