High sensitivity chipless RFID humidity sensor tags are based on SnO2/G nanomaterials

In this study, a chipless RFID humidity sensor tag based on SnO2/G (Graphene) nanomaterial with recognition and sensing functions is proposed. Chip-less RFID sensors are usually composed of tag ID and sensing materials. In this paper, similar nano-spherical SnO2 powder was generated by hydrothermal method and doped with G to get SnO2/G mixture. For chip-free RFID tags, a microstrip coupled line resonator is proposed, which consists of a coupled line segment and three line segments of different shapes. Among them, u-shaped resonators coated with humidity sensitive materials for humidity sensing, and the other two resonators can code four different states. Through testing the sensitivity, hysteresis, repeatability and response characteristics of humidity sensor, it is proved that humidity sensitive material has excellent humidity sensing performance. At 11%-98%RH, the frequency offset is up to 257 MHz, achieving a sensitivity of 2.95MHz/%RH. HFSS simulation and experimental results verify that the proposed integration of humidity sensor and RFID technology has great application potential.