Two-Bit Chipless RFID for Temperature and Humidity Sensing

A new compact chipless radio frequency identification (RFID) temperature and humidity sensor is presented. New microstrip coupled line resonator is suggested to simultaneously support four state ID data and extra sensing information. The resonator consists of coupled line section and three line elements (arms). The longest arm, connected all the time, is particularly designed for either temperature or humidity sensing and has resonance f1. The other two arms are used for encoding four different codes. The resonator connections can be adjusted for one of the four states: 100, 101, 110, and 111, showing, resonance at f1, resonance at both f1 and f3, resonance at both f1 and f2, and resonance at f1, f2 and f3, respectively. The change in f1 can be directly converted to either object temperature or environmental humidity. A multi-resonator structure with six resonators is designed and implemented for RFID tags applications. Two of these resonators are designed based on the suggested structure to include temperature and humidity measurements. Measurement and simulation results are in good agreement.