Encoding Capacity Enhancement for Chipless RFID Tag Using Resonant Frequency Placement

In this study, a novel encoding approach for chipless radio frequency identification (RFID) tags is proposed. This tag is designed with
$N$
resonant elements, each of which can be parameterized to resonate at
$M$
individual desired frequencies. Therefore, the number of encoded data points is
$\sum \nolimits _{k=0}^{N} C_{k}^{N\times M}$
. The introduced design concept is supported by a new mechanism to deal with the mutual coupling effect between elements, thus making the tag resonate at any desired frequency. The proposed mechanism is based on applying the particle swarm optimization (PSO) algorithm in the optimization of the tag structure parameters so that the resonant frequencies approach those determined by the user in advance. Simulation and experimental results show that the proposed approach not only overcomes one of the most troublesome pitfalls in designing chipless RFID tags, which include the limitation in data encoding capacity while keeping the tag small and uncomplex, but also changes the steps the tags are designed in such a way that the resonant frequencies can be determined before designing the tag structure.