Characterization of Electro-textiles Using Wireless Reflectometry for Optimization of Wearable UHF RFID Tags

Flexible and maintenance-free wearable ultra-high frequency (UHF) radio frequency identification (RFID) tag antennas are desired in wireless sensor systems in security, healthcare, and biomedical applications. Optimization of wearable antennas demands comprehensive knowledge of the electrical properties of the conductive electro-textiles used in the antenna structure. In this paper, we first propose a wireless reflectometry technique to accurately extract the sheet resistance of various electro-textiles. The technique relies on the measurement of the resonant peak of a scatterer. Its bandwidth and magnitude are strongly correlated with the conductive losses of the strips so that a relationship can be extracted. We then demonstrate that the electro-textiles, including conductive fabrics and embroidery textiles, can be accurately modeled using the sheet resistance as the only conductive material parameter for wearable antenna design.