RF-Gaussmeter: Noninvasive μT-level Magnetic Field Sensing using TMR-based RFID Tag

摘要

Magnetic field sensing is essential for electrical safety and early hazard detection. While existing solutions are generally considered reliable and accurate, they are hindered by battery-dependent challenges, invasive detection, and poor scalability. To address these limitations, in this paper, we propose a novel μT-level magnetic field sensing method based on RFID tags, named RF-Gaussmeter. The design of RF-Gaussmeter involves embedding a Tunnel Magnetoresistance (TMR) sensor into the COTS RFID tags. We consider the magnetic field generated by current-carrying conductors as the sensing target. When the TMR sensor captures the magnetic field generated by a conductor, it can output the sensing voltage signal to the RFID tag, altering the chip’s impedance and thereby influencing the received signal. To amplify weak magnetic fields, we explore the interaction model between the MOSFET in RFID tags and differential voltage signals. Based on this model, we propose a differential signal amplification design based on RFID to enhance sensing sensitivity. To extract the magnetic-field-related sensing features, we develop a self-differential module based on RFID to remove multi-path interference. Experimental results show that RF-Gaussmeter achieves an absolute error of 0.0825A for current sensing and 1.32μT for magnetic field sensing within 80cm range, demonstrating excellent practicality and accuracy.