Fundamental Characteristics of Electro-Textiles in Wearable UHF RFID Patch Antennas for Body-Centric Sensing Systems

Electro-textiles feature excellent radio frequency (RF) performance. They have an enormous potential to be widely accepted in body-centric sensing systems as wearable antenna materials. However, the RF community lacks comprehensive knowledge of electro-textile fundamental characteristics. This paper provides critical electro-textile design parameters for wearable radio frequency identification (RFID) ultra-high-frequency (UHF) patch antennas. For the first time, modeling parameters for embroidered antenna ground plane and patch structures are established and verified. The results highlight a new unprecedented fundamental characteristic of embroidered antennas: all embroidered structures, modeled as uniform and infinitely thin textile layer, have an existing imaginary part in their sheet impedance modeling parameter. It accounts for the antenna input inductance contributed from the electro-textile. Ideally, such as for highly conductive fabrics and pure conductors, the imaginary part is negligible. Utilizing the proposed design guidelines, a fully wearable and flexible embroidered RFID patch antenna is for the first time realized. Its performance may be considered as a benchmark for future designs. The design parameters and findings form an important milestone in the development towards wearable intelligence and foster industrial developments of garment-integrated RFID antennas.