Setup-Independent Sensing Architecture with Multiple UHF RFID Sensor Tags

Ultra High Frequency Radio Frequency Identification (UHF RFID)-based sensing technology with antenna-integrated sensor tags offers a cost-effective solution for Internet of Things (IoT) applications. A multi-dimensional differential measurement technique for eliminating the effect of measurement setup, such as unknown mutual distance and orientation between the read/write device (RWD) and sensor tags, and line-of-sight obstruction, on acquiring information from multiple sensor tags simultaneously is proposed. The concept is based on 1) using a channel hopping mechanism to acquire multi-dimensional datasets and 2) conducting a dissimilarity analysis between offline and online datasets to extract sensor information. The differential measurement, which is activated by the channel hopping mechanism, mitigates the impact of the measurement setup, making the pattern of the multi-dimensional datasets tightly relate to the sensing state. A sensor tag for measuring the water filling level of polyvinyl chloride (PVC) pipes is designed and fabricated. Experiments show that the proposed method can accurately acquire information from three sensor tags simultaneously under different measurement setups. The performances using datasets of different dimensions are compared. Results reveal that using low-dimensional datasets can still be capable of getting accurate information from the sensor tags, implying that the acquisition time can be reduced.