A wearable UHF RFID tag antenna with Archimedean spiral strips

In this work, a wearable RFID tag antenna is proposed. The antenna employs Archimedean spiral strips, minimizing the antenna's size. To adjust the input resistance, the antenna uses T-Match technique. The ultimate size is a circular with a diameter of 32 mm with the center frequency of 915 MHz. For low-cost fabrication, the antenna is only one-layer copper. Good match with two different types of chip are achieved. Furthermore, we simulated two different environments, one is air and the other is on wrist, and both have good performances in terms of reflection coefficients and gain. In air, the reading distance is up to 12 m and shows a good omni-directivity. When used on wrist, the reading distance is up to 8 m and presents unilateral directivity.