High Sensitivity Passive Wireless Humidity Sensor Based on Polyvinyl Alcohol

A low cost and compact chipless Radio Frequency Identification (RFID) humidity sensor with the size of 18 * 18 * 0.5 mm(3) is designed for environmental humidity monitor. The sensor consists of a circular resonator and a rectangular substrate, which utilizes the polyvinyl alcohol (PVA) humidity sensitive material for relative humidity (RH) sensing. The PVA humidity sensitive material covers the sensor surface. The working principle of the sensor is that the change of environmental humidity results in the changing of dielectric constant of PVA and thus shifting of the resonant frequency of the sensor. The real-time humidity can be observed by monitoring the resonant frequency. The simulation results show that the humidity sensing range of the designed humidity sensor is 21.9%RH similar to 52.5%RH, corresponding to the resonant frequency range of the sensor from 2.76 GHz to 2.51 GHz with the total offset 250 MHz. The maximum humidity sensitivity was 23.08 MHz/%RH within the monitoring range. The designed humidity sensor has the advantages of low cost, compact and simple structure, which is suitable for humidity monitoring in various complex environments.