A Novel Flexible Chipless RFID Tag Sensor for Monitoring Environmental Humidity

The rapid development of radio frequency identification (RFID) technology has significantly changed the method of structural health monitoring (SHM). In this article, a novel flexible chipless RFID tag sensor is proposed to monitor the change of relative humidity (RH) in the environment around structures. The tag is fabricated on a flexible substrate that can be transferred to a bendable metal surface and is fused with a high encoding capacity for tag recognition. In addition, a low-cost detection and wireless transmission scheme for dynamic spectrum data transmission is used, which is more flexible and automatical than traditional detection methods. The simulation and experiment results show that the humidity sensitivity of the tag sensor coated with a polyvinyl acetate (PVA) film is about 0.584 MHz/RH in the RH range below ${60}\%$ , and about 2.03 MHz/RH in the higher RH range. Meanwhile, the tag can maintain stable sensing performances in a certain bending range, which may be very desirable in many application scenarios.