Abstract
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 f(1). 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 f(1), resonance at both f(1) and f(3), resonance at both f(1) and f(2), and resonance at f(1), f(2) and f(3), respectively. The change in f(1) can he 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.