Magnetic signal scan imaging system based on giant magnetoimpedance (GMI) differential sensor

This paper presents the design and implementation of a magnetic signal scanning and imaging system based on the giant magnetoimpedance (GMI) effect. The system employs a pair of performance-matched GMI sensing elements configured as a differential probe structure. Through co-optimized low-noise electronic and probe design, the system effectively suppresses both intrinsic sensor common-mode drift and external environmental magnetic noise, enabling high signal-to-noise ratio detection of nano-tesla to micro-tesla-level magnetic signals without magnetic shielding. Experimental results demonstrate that the differential system achieves significantly lower noise spectral density in the given unshielded environment compared to conventional GMI sensors (46 pT/Hz vs 286 pT/Hz at 1 Hz), with sensitivity of 186 790 V/T and spatial resolution better than 200 μm. Through scanning experiments on magnetic ink patterns in banknotes and on magnetic reference samples, as well as spatial resolution tests, the system's excellent performance in weak magnetic field detection and spatial resolution was verified. Compared to superconducting quantum interference device scanning systems, which require liquid helium cooling, this system based on the GMI effect offers advantages of room-temperature operation, compact structure, and low cost. Relative to conventional single-element GMI microscopes, it achieves significant improvements in signal-to-noise ratio and environmental adaptability. This research provides a practical solution for high-resolution magnetic field imaging at room temperature, with broad application potential in materials magnetism, biomagnetic imaging, and nanomagnetic detection.