Conditions and Limits of Calibration-Free Magnetic-Field Measurement: A Minimal Model with In Situ Augmented-Reality Visualization for Wireless Power Transfer.

Accurate magnetic-field characterization is essential for evaluating wireless power transfer (WPT) systems. Conventional near-field measurements require setup-specific probe calibration, increasing experimental complexity. This paper proposes a calibration-free framework based on a minimal small-loop magnetic-field probe model derived from Faraday's law, where the voltage-to-magnetic-field conversion coefficient is analytically determined from probe geometry and operating frequency. Its validity is examined by comparing an ideal analytical model, a spatially aware Bessel-function-based model, and full-wave simulations. Full-wave simulations indicate that the loop circumference should remain within approximately 0.1λ for the modeled probe, while experimental validation at 13.56 MHz supports the method in the tested WPT configuration. Combined with three-axis measurement and augmented-reality (AR) visualization, the method enables practical three-dimensional (3D) magnetic-field mapping.