High sensitivity chipless RFID humidity sensor tag based on PVA film

In this paper, a chipless RFID humidity sensor tag for integrated sensor for Internet of Things applications is proposed. By improving the square resonator, the surface of the sensor tag is covered with polyvinyl alcohol (PVA) film. Through the electromagnetic simulation software, the influence of the resonator structure parameters on the resonant characteristics is deeply analyzed, and the working frequency band and the size are optimized. In addition, the effects of different permittivity values on the resonant response are studied. The simulation results show that with the relative humidity changing from $29.1 \% \mathrm{RH}$ to $90.9 \% \mathrm{RH}$, the resonant frequency presents a significant shift to the left, with a total shift of 620 MHz and a sensitivity of 10.03 $\mathrm{MHz} / \% \mathrm{RH}$. The sensor labels designed are flexible and low cost, and can be deployed to a variety of low-cost sensor applications.