Etiquetas RFID sem chip baseadas em ressoadores de microfita e em seções de linhas de transmissão em "C".

Abstract

Chipless RFID tags have been introduced as a reliable and low cost solution for implementation of identification systems, since the cost of an RFID system basically depends on the integrated circuit in the tag. Thus, the main challenges are how to codify data without the presence of a chip and how to increase the quantity of bits written in a tag. Currently, the most popular information encoding technique is based on the generation of a particular signature in the spectrum of the backscattered signal, what is obtained by using resonant structures working as a band rejection filters, designed to resonate at defined frequencies. In this work, a parametric analysis resonator designs, especially spiral resonators, was performed in order to design chipless RFID tags in frequency domain for applications in identification and sensing by using flexible substrates. Using an electromagnetic simulation software and laboratory measurements, from scattering parameters, the performance of the proposed microstrip resonators were analyzed. In order to improve the coding capacity of chipless RFID tags based on resonators spiral, it was proven through simulated results of radar cross section (RCS) and electric field, the possibility of simultaneous use of vertical and horizontal polarizations in writing data. In order to also increase the capacity of chipless RFID tags in time domain, a parametric analysis of dispersive coupled transmission line folded C-sections was conducted by simulation. The results confirmed the feasibility of the utilization of this concept with multi-layer C-sections in encoding technique based on group delay. It has been found that this technique provides a significant amount of group delay and narrow band group delay peaks, allowing a greater coding data. Therefore, the technique with folded multi-layer structure of C-sections was used in the design of chipless RFID tags on flexible substrates. The study of a couple of types of substrates, simulations of several chipless tags configurations and measurements with prototypes made on two types of flexible substrates were performed. It has been shown that the peak group delay can be varied by changing the length and width of C-sections and the results confirm once again the possibility of utilization of this technique. Compactness due to the folding technique and robustness due to the coding in time domain are the major advantages of this presented chipless solution.