Hybrid Encoding Method for Radio Frequency Identification in the Internet of Things Systems

As one of the important components of internet of things (IOT) systems, radio frequency identification (RFID) tags need to be improved in terms of power consumption, size reduction and coding capacity. In conventional methods, designers focus on optimizing resonators, but by focusing on the use of phase coding, a new method can be presented that results in a tag with smaller dimensions and more coding capacity. Hybrid encoding for RFID is based on the phase coding by changing the position of the resonator in the chipless RFID tag. In this paper a C-shaped resonator is proposed to design a chipless tag on the Rogers RT/duroid 5880 laminates. This method proposes different phase values in the resonance frequency as separate codes. The difference between the phases of the scattering parameters S11 and S22 is measured to show the effect of position varying of the proposed C-shaped resonator. With the three different values of at the resonance frequency, the proposed RFID tag creates codes 0, 1 and 2, in comparison with the conventional structures that create codes 0 and 1 only, based on the presence or absence of a transition zero at the resonance frequency. The proposed structure was designed, fabricated and measured and measurement results validate this method. Accordingly, an RFID tag with five C-shaped resonators is proposed, where the simulation results of its $3^{5}=243$ different states are presented in this paper.