A Depolarizing Chipless RFID Tag with Humidity Sensing Capability

A novel compact depolarizing chipless RFID tag is investigated for humidity sensing. The proposed chipless tag is based on three nested scatterers with the resonant frequencies in the band covering from 4 GHz to 7.5 GHz. The innermost scatterer is used to monitor humidity variation, while the outer two resonators are introduced to encode 6-bit data through using frequency shift encoding method. Polyvinyl alcohol (PVA) film is deposited on the surface of the sensing resonator, making it sensitive to the humidity. The relative humidity information is encoded in the deviation of the resonant frequency. In addition, the tag has a compact size of 15 x 15 x 0.8 mm(3) with depolarizing characteristic which can increase the robustness of detection in complex environments.