In Situ Calibration Method for an MGT Detection System Based on Helmholtz Coils

Area of Science:

• Geophysics
• Sensor Technology
• Instrumentation

Background:

• Vector magnetometer arrays are crucial for detecting ferromagnetic targets and measuring magnetic gradient tensor (MGT) data.
• Existing calibration methods suffer from mechanical noise, orientation instability, and poor repeatability due to rotational requirements.
• Sensor errors include proportional factors, non-orthogonality, and magnetic interference, limiting measurement precision.

Purpose of the Study:

• To develop an in situ rapid calibration method for MGT systems that overcomes the limitations of traditional rotational techniques.
• To improve the accuracy, consistency, and reliability of vector magnetometer array measurements.
• To enable high-precision MGT calibration without mechanical rotation or specialized environments.

Main Methods:

• Utilized triaxial Helmholtz coils to generate controlled, three-dimensional magnetic fields of constant magnitude and random directions.
• Kept sensors stationary during calibration, replacing conventional rotational excitation.
• Developed a two-stage rapid calibration algorithm for individual sensor error modeling and array relative calibration.

Main Results:

• Significantly reduced the tensor invariant C_T from 6287.84 nT/m to 7.57 nT/m.
• Decreased the variance of C_T from 1.46 × 10⁶ to 13.47 nT²/m².
• Suppressed inter-sensor output differences to 1-3 nT and magnetic field magnitude error to 3 × 10^-4 nT, a 5-6 order-of-magnitude improvement.

Conclusions:

• The proposed in situ calibration method effectively eliminates rotational errors and enhances array consistency.
• Achieved high-precision MGT calibration with substantial improvements in accuracy and repeatability.
• Demonstrated strong engineering value for practical applications in ferromagnetic target detection and geophysical surveys.