Structural Design of a Concentrating Magnetic Ring for TMR-Based Current Measurement

To investigate the stability and sensitivity of magnetic field signals in current measurement systems, this paper presents a comprehensive finite element simulation study of three magnetic core structures: toroidal, U-shaped, and externally open types. Three-dimensional models were constructed in COMSOL Multiphysics, incorporating identical material properties (Permalloy), fixed thickness, and uniform boundary conditions to ensure comparability. A copper conductor carrying currents from 100 A to 1000 A was introduced as the excitation source, and a probe was placed at the sensor location to record magnetic flux density. In addition, the maximum flux density inside the core was monitored to evaluate magnetic saturation. Parametric sweeps were performed across the full current range to analyze the impact of core geometry on magnetic field concentration and uniformity. Simulation results show that the toroidal core offers strong magnetic field concentration, the U-shaped core ensures uniform field distribution in the sensing region, and the externally open core achieves a trade-off between field uniformity and concentration. However, quantitative analysis reveals that the externally open structure experiences local magnetic saturation at higher currents, which may affect linearity and accuracy. These results provide detailed theoretical guidance and structural optimization strategies for magnetic cores in magnetic-field-based current sensors.