Design of planar resonators on flexible substrate for chipless tags intended for crack sensing

At the moment, the most popular information encoding technique is based on the generation of a particular signature in the spectrum of the backscattered signal. Chipless tags which rely on spectral signature encode data by using resonant structures working as band rejection filters, designed to resonate at defined frequencies. In this paper, a parametric study of different layouts of spiral resonator coupled to a transmission line and band rejection filters on flexible substrate, namely a 100 um thick PET substrate, operating in the 2-4 GHz band is firstly performed with the aim of designing a chipless tag working either as identifier or sensor. The design has been carried out by means of an electromagnetic CAD, and the performance of the proposed structures has been evaluated by the analysis of the respective S-parameters. Then, a proof of concept of a novel passive, wireless and chipless crack sensor has been introduced as practical example.