Meander Resonator Coupled UHF RFID System for Biomechanics Sensing Applications

Abstract

This paper presents a biomechanics sensing system based on an ultra-high frequency (UHF) RFID tag coupled with a meander resonator for motion tracking and displacement sensing. The variations in their relative position alter the strength of mutual coupling, leading to impedance changes in the RFID tag antenna. These impedance variations modulate the power reflection coefficient, which in turn affects both the backscattered signal strength (RSSI) and the turn-on threshold power of the RFID tag. The performance of the system was evaluated through simulations and experimental validation, demonstrating a 14 dB reduction in RSSI and a 5 dBm increase in threshold power over a displacement range of 30 mm. The system was further validated for wearable movement sensing in knee flexion tracking, where results indicated an RSSI variation of around 12 dB as the knee angle changed from 115° to 175°. Additionally, the turn-on threshold power ( $ P_{\text {th}} $ ) exhibited a strong correlation with knee flexion angles, achieving a coefficient of determination ( $ R^{2} = 0.973 $ ) based on curve-fitted data. These results validate the feasibility of the proposed system for wearable body motion monitoring in healthcare applications.