A Flexible UHF RFID Respiratory Sensor

Abstract In this study, we developed a Radio Frequency Identification (RFID) sensor to monitor respiratory rates. The sensor utilizes a passive RFID tag enhanced with a metamaterial-inspired structure to boost its maximum gain value. This gain increased from -0.39 dBi to 0.57 dBi. Monitoring of the respiratory rate was conducted by analyzing variations in the Received Signal Strength Indicator (RSSI), which were influenced by respiratory movements. The RSSI data collected from the RFID tag readings were processed using the Daubechies wavelet of order 5 (db5) with three levels of signal decomposition, resulting in signals with reduced noise. These measurements were particularly effective when the participant was at rest, with the RFID tag positioned over the abdomen. The maximum reading range obtained was 1.04 m. The respiratory rates derived from the RSSI variations were validated against a vital signals monitor, confirming that they fell within the expected frequency variation range of the multiparameter monitor.