Abstract
A compact passive two-bit metamaterial based phase-modulated chipless RFID tag with a temperature sensor, operating at 2.4 GHz, is presented in this paper. The chipless RFID tag consists of the following: (i) composite right/ left handed (CRLH) based antenna operating at 2.4 GHz; (ii) CRLH delay lines operating in the left-handed (LH) region at 2.4 GHz; (iii) digital phase modulating sections realized using the distributed approach; and (iv) thermistor for temperature sensing. The phase of the backscattered signal over a period of time is used for identifying a particular tag and sensing the temperature. QPSK is implemented by using the four phase modulating sections, which have unique input reflection coefficients corresponding to the four symbols, and analog phase modulation is used for temperature sensing. The dimensions of the chipless tag with two-phase modulating sections at the operating frequency of 2.4 GHz are 0.86 lambda(0) x 0.16 lambda(0) x 0.00648 lambda(0). A footprint reduction of 28% is achieved in comparison to the conventional chipless RFID tags, and is realized by using a monopole antenna, lumped-element-based phase-modulating sections, and delay lines. Measurement and simulation results show that the proposed RFID chipless tag with temperature sensor is compact and delivers the desired performance as specified.