Cost-Effective Wireless Impedance Measurement for RFID Tag Antenna

Wireless passive sensor based on the radio frequency identification (RFID) tag antenna has been widely used in structural health monitoring (SHM). The access of RFID technology to the 5G network is envisioned in 5G advanced technology. For the RFID tag sensor, the accurate and wireless determination of its antenna input impedance is a practical problem for ubiquitous sensing. In this paper, we propose a cost-effective wireless passive method for the measurement of tag antenna input impedance, which only requires an RFID reader and a low-complexity impedance tuning circuit. The proposed method can be used to track the impedance variation of RFID tag antenna for ubiquitous sensing.