Calibration method for planar SQUID gradiometers based on the magnetic gradient tensor components

Abstract

The accuracy of tesla/volt calibration factors for superconducting quantum interference devices (SQUID) gradiometers is essential to take advantage of the magnetic gradient tensor (MGT), but the accuracy of the published calibration procedures ranges from tenths of percent to a few percent. In this paper, we propose an efficient calibration method for planar SQUID gradiometers based on MGT components. The factors affecting the calibration accuracy and the optimal inclination angle for calibration were investigated by analyzing the response characteristics of planar SQUID gradiometers to the MGT components. By superposition of square coils and gridding of pickup loops, numerical models of the response of planar gradiometers to different types of Maxwell coils were built to simulate theoretical calibration accuracy and calibration errors due to position, attitude and imbalance. We built a calibration setup to achieve high-precision simultaneous calibration of multi-channel planar SQUID gradiometers and investigated the effect of eddy current on the calibration accuracy. The results show that simulation and experimental results are in general agreement by taking into account various error factors. A calibration error of about 0.4% is achieved.