A Locating Harmonic Radar-Based Sensor for Vital-Sign Health Monitoring With Ultra-Low Power Harmonic Conversion Loss Compensation

As living standards improve, the demand for health monitoring continues to rise. The daily continuous monitoring over the long term is still facing challenges due to limited technology advances with well body comfort. This article proposes a wireless nonintrusive sensing system based on a harmonic radar sensor (HRS) system. The HRS transponder is used as a sensing node placed on the surface of the target’s thoracic cavity. Through an I/Q-modulated harmonic reader architecture, information from the HRS is acquired. The amplitude and phase information demodulated by the HRS transceiver are used for vital sign detection and target localization, respectively. In this study, we successfully conduct the wireless harmonic sensing experiment for vital sign sensing with the capability for transponder localization. The measured vital sign signals show a good consistency with commercial electrocardiograph (ECG) reference signals in terms of heartbeat intervals. Furthermore, the system achieves precise localization of the transponder, with a positioning error of less than 6 cm with the probability of 95%. Empirical evidence demonstrates that the proposed HRS-based system exhibits superior and more stable detection performance compared with conventional passive harmonic methods. Furthermore, our proposed active HRS extends the maximum detection range of passive harmonic tags from 2 to 3 m. This improvement arises from the system’s active architecture, which integrates a reflective amplifier to enhance signal strength by 12 dB at 1.8 GHz. The experimental results also indicate that the wireless sensing architecture based on HRS in this work is a potential candidate for future healthcare systems.