An octagonal-shaped conductive HC12 & LIBERATOR-40 thread embroidered chipless RFID for general IoT applications

Abstract

This paper presents the design, fabrication and testing of two embroidered chipless octagonal-shaped RFID tags on cotton fabric for wearable applications. The first tag is designed by using silver-coated polyamide conductive fibre (HC12) and the second tag is embroidered by using highly conductive Vectran (LIBERATOR 40) which is highly conductive multifilament yarn spun from Liquid Crystal Polymers (LCP), on cotton fabrics. In contrast to the traditional RFID tag, the chipless RFID tagging, the ID code is not saved in the memory, instead, it uses the physical features of the tag to send data. The proposed tag's design uses a Frequency Selective Surface (FSS) technique for the frequency range of 8–18 GHz. These tags are designed using CST studio and precisely fabricated by using commercial ZSK Technical Embroidery System JCZA (0109–550). The tag design is composed of six concentric octagonal loop resonators with one unitary element. The electromagnetic scattering waves behaviour and Singularity Expansion Method (SEM) based circuit modelling for the octagonal-shaped tag is performed, and the coupling coefficients are evaluated. The desired data bits are obtained by a series of comparative experiments for Radar Cross Section (RCS) in an anechoic chamber. The experimental results obtained show that the 4-bit data is accurately retrieved with the variation of distance by up to 1.8 m at 0 dB m. Moreover, the average transition from minimum ‘0’ to maximum 1’ is -27 dB for both designs. Furthermore, the experimental results for on-body RCS measurements and the bending effects on both tags down to 7 mm is observed. This octagonal embroidered Chipless RFID tag is a fully textile design which is compact and can be deployed commercially in various IoT applications.