High-Frequency Thin-Film Magnetic Sensor for Precise Magnetic Near-Field Measurement

Highly sensitive magnetic field sensors are essential for applications such as biomedical diagnostics and electromagnetic compatibility (EMC) assessments. This study focuses on optimizing a GHz-range thin-film magnetic sensor by incorporating a slit pattern in the magnetic layer, which improves impedance matching and current distribution. Amorphous CoNbZr thin-film sensors with slit widths ranging from 0 μm (no slit) to 50 μm were fabricated. Among these, the 10 μm slit design exhibited the best impedance matching and magnetic field sensitivity. Additionally, a carrier suppression circuit was implemented to reduce phase noise, resulting in improved sensitivity, achieving a minimum detectable field of 1.41 × 10⁻¹¹ T/√Hz. The sensor was employed for precise near-field measurements in wireless power transfer (WPT) systems, where it outperformed conventional loop antennas. Experimental results demonstrated superior sensitivity and enhanced spatial resolution, particularly near the ferromagnetic resonance under specific DC bias and carrier frequency conditions. These findings highlight the potential of the optimized sensor for improving electromagnetic interference (EMI) and EMC assessments. © 2025 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.