Characterizations and Optimization Techniques of Embroidered RFID Antenna for Wearable Applications

Embroidering antennas and coils directly onto fabrics is the ideal solution for RFID (UHF or HF) deployment in apparel and garment industry. However, RFID tags embroidered with conductive yarns have several limitations in their design and performance. 1) antennas cannot utilize geometries with higher resolution, 2) yarns have higher resistivity than metallic materials, and 3) the parasitic capacitance will be introduced inside the micro-structures as well as between the threads. These issues all limit the performance of embroidered RFID tags. In this paper, we explore quantitatively the limitations of embroidered antenna designs, and propose the guideline to design embroidery-friendly RFID antennas to achieve a satisfactory performance. Several UHF RFID tags with embroidered antennas and coils are prototyped, and their performance is comparable to traditional metallic antennas based on polyethylene terephthalate (PET) substrate.