A Flexible Chipless RFID Sensor for Humidity Detection

In this paper, a novel flexible chipless radio-frequency-identification (RFID) sensor is proposed to monitor the change of relative humidity (RH) in environments. The monitoring is realized by coating a humidity-sensitive polyvinyl alcohol (PVA) film on the surface of the resonant structure of the RFID tag and measuring the change on the relative permittivity of the material caused by the change of RH. The change of relative permittivity can produce the shift of resonant frequency of the tag, which can be recorded by the RFID reader. Simulation results show that the maximum humidity sensitivity of the tag with a coating of film is about 2.03 MHz/RH. Also, the tag has been extensively tested for bending and it performs very well, showing its good flexibility.