Design of Uniform-Field Coils With Adjustable Coil Constant for Calibration of Triaxial Magnetometers Across Different Magnetic Field Ranges

The calibration of a triaxial magnetometer (TAM) relies on a high-precision reference magnetic source that provides a known magnetic field, and its accuracy directly determines the final calibration precision. To address the challenge of calibrating TAMs across widely varying measurement ranges found in diverse applications, this article proposes a coil design method featuring an adjustable coil constant (ACC). By integrating the target field method (TFM) and the nondominated sorting genetic algorithm II with adaptive penalties (AP-NSGA-II), the coil structure is optimized to generate controllable magnetic fields spanning multiple orders of magnitude. This design enables the generation of a highly uniform magnetic field over a large central volume without relying on current sources with multiple output ranges. Experimental results demonstrate that the maximum magnetic field nonuniformity is 0.433% across different ACC settings, aligning well with design expectations. Furthermore, by combining the proposed system with the differential evolution (DE) algorithm, TAM calibration was performed at magnetic field intensities of 30000 and 100 nT, achieving postcalibration residuals of 2.32 and 1.97 nT, respectively. Experiments verify that the coils designed with this method can provide high-precision, uniform reference magnetic fields for calibrating different types of TAMs across wide measurement ranges.