Data Encoding Improvement and Size Reduction of Chipless RFID Tag Using Short-circuit Line Effect and Angle-based Divided Loops ☆

This paper focuses on short circuit and concentric loop effects to improve the structure dimension as well as enhance the ability to encode electromagnetic wave data for chipless RFID tags. The tag is composed of star-shaped rings which are concentricly nested together. The following factors help reduce the tag size: using the phenomenon of electromagnetic backscattering, assessment by the Radar Cross section (RCS), the antenna-free tag only includes the multi-frequency resonators. The number of resonant peaks increases exponentially with the number of concentric rings of the tag, thereby not increasing the size when the number of encoding bits is needed. By using short-cuts, we can divide the star into smaller loops, each creating a unique resonant peak. Using concentric loops, the tag can multiply the binary coding to multiple bits without increasing the overall dimension. By inserting the short circuit lines at different angle between the two consecutive loops, we can adjust the resonant frequency in the frequeny bands, thereby changing the value of the bit by shifting the frequency position. The proposed tag is a magnetic frequency domain tag to help prevent against the influence of environment. The overall dimension of the resulted tag is 13mm x 13 mm and the tag is aimed to be a printable tag on the flexible substrate to minimize the fabrication cost. With the 18-vertex star-shaped tag with five concentric loops, this chipless RFID tag can encode up to 16 bits with high resolution and large data density.