UHF RFID Antenna Sensor System Using Optimal Power-Oriented Setup-Independent Technique

Ultrahigh-frequency radio frequency identification (UHF RFID) with a transducer-integrated antenna offers a cost-effective sensing solution for industrial applications. However, the analog backscattered signal contains the coupling effects between the antenna's nearby environment and the unknown measurement setup, such as mutual distance and orientation between the read/write device (RWD) and sensor tags, and line-of-sight obstruction, which affects measurement accuracy. This article proposes an optimal power-oriented setup-independent technique that utilizes commercially self-tuning RFID tags to extract the environment in the vicinity of the antenna, independent of the measurement setup. The concept is based on an observation that the level of the radiated power of the RWD and the received power of the self-tuning RFID IC are linearly regressed. The condition of the environment is identified by the self-tuned value from the RFID chip under an optimal chip impedance. In the offline state, the optimal received power level is determined to maximize the pairwise Euclidean distance of the tuned values of the environment state near the tag. The radiated power level of the RWD is adjusted linearly to implement the sensing at the optimal power level. A water-filling sensor tag operated with polyvinyl chloride (PVC) pipes is demonstrated. Experiments show that the proposed system provides accurate sensing information under different measurement setups. The RFID tags can also be used in installations with heterogeneous environments. The proposed technique has been experimentally validated by applying it to two sizes of PVC pipes, confirming the sensing accuracy and adaptability.