Wireless Temperature Sensing Yarn Based on UHF RFID Helix Dipole Hybrid Antenna

Existing radio frequency identification (RFID) temperature sensors in the wearable field involve issues such as poor comfort level, high costs, low flexibility, and concealment. There is an urgent need to develop flexible wireless temperature sensors with yarn-like structure, low cost, and good reading performance. In this work, an ultrahigh-frequency (UHF) RFID temperature sensing yarn was designed by the principle of impedance mismatch between antenna and RFID chip as well as an incorporation of a miniature thermistor, and then, the prototype was prepared and evaluated on its sensing performance. The receive signal strength indication (RSSI) of the developed sensing yarn with the right helix structure exponentially varied with temperature, and it showed excellent capability in wireless sensing temperature. It has great potential for application in intelligent health monitoring such as body temperature and respiration monitoring.