High-Frequency Weak Magnetic-Field Detection and Dose Calibration for Micro-Magnetic Stimulation: A Review.

High-frequency weak magnetic fields generated by submillimeter micro-coils are key physical parameters associated with stimulation dose in micro-magnetic stimulation (μMS). However, their low amplitude, highly localized near-field distribution, frequency-dependent probe response, and sensitivity to coupling variations make accurate measurement and dose calibration challenging. This review summarizes recent advances in high-frequency weak magnetic-field detection techniques for micro-coil systems. It discusses key measurement challenges, including probe parasitics, impedance mismatch, phase distortion, spatial averaging, and dynamic detuning. Existing methods are classified into direct magnetic-field measurement, resonance-enhanced detection and calibration, spatial-field mapping reconstruction, and adaptive compensation. These methods are compared across five dimensions: frequency range, sensitivity, spatial resolution, system complexity, and online integration capability. The review further highlights the need to establish reliable and traceable relationships among detector outputs, local magnetic fields, and stimulation dose. Future directions include broadband adaptive measurement, online dose calibration, multichannel magnetic-field imaging, multichannel magnetic-field component decoupling, and physics-constrained data-driven field estimation. Overall, this review provides a structured overview of micro-coil magnetic-field measurement, stimulation dose standardization, and the quantitative frameworks for closed-loop neuromodulation microsystems.