Dual-Polarized Chipless RFID Tag With Simultaneous Identification and Sensing

This paper proposes a compact and low-profile chipless RFID sensor, with identification and sensing capability, the latter enabled by permittivity variation of integrated liquid. The design comprised one modified meander line that backscatters the horizontal polarization (sensing polarization) and two meander lines that backscatter the vertical polarization (identification polarization). The proposed sensor can detect the appearance of liquids and its volume based on the liquid’s permittivity (from 1 to 15) using only resonant peaks of S11. Furthermore, it is capable to simultaneously executing sensing and identification, i.e. the measurement results can be linked with the unique tags ID. The sensor is demonstrated for detecting cold-chain breaks in frozen food applications, and soil moisture content. However, any other application where a material changes its permittivity based on sensed value is feasible. The proposed tag has a narrow peak with a 3-dB Q-factor of 16.8 in sensing polarization and 35.8/14.4 for ID1/ID2 in identification polarization, owing to its small size of 0.2 x 0.2 λ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (at 6.3 GHz).