A high sensitivity capacitively-loaded UHF RFID temperature sensor tag using PTFE material

A capacitively-loaded passive RFID temperature sensor tag working at UHF band is designed and tested. A cavity backed slot antenna is designed as the tag antenna. In order to realize high temperature sensitivity, the Polytetrafluoroethylene (PTFE) material which has a large thermal expansion of 140ppm/°C is used as the temperature sensing material. A copper coated PTFE post is placed at the center of the cavity, which is in close proximity to the cavity ceiling. Thus, a loaded capacitor is generated between the PTFE surface and the cavity ceiling. As the temperature increases, the PTFE will approach to the cavity ceiling due to the thermal expansion, and thus change the loaded capacitance; therefore, the resonant frequency of the slot antenna will change accordingly. By distinguishing the resonant frequency of the antenna, the temperature information is obtained. The simulation results show that this design provides a frequency shift of 30MHz/10°C and a read range of 10.5m.