UHF RFID Antenna Sensing System and Its Application


Student thesis: Doctoral Thesis

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Award date11 Aug 2022


The Internet of Things (IoT) technology integrates computing, communication, and control on the basis of comprehensive perception to provide more automation services. Low-cost Ultra High Frequency Radio Frequency Identification (UHF RFID) can provide a general battery-less sensing technology for smart cities and factories. In this thesis, the sensing unit is integrated with the RFID tag antenna, the read/write device (RWD) can realize the near-field state of the antenna by analyzing the parameters of backscatter signals. This thesis focuses on setup-independent passive sensing algorithms and a RFID-based PVC pipe water-filling level sensor system. The main contents are as follows:

1) Multi-dimensional differential method based on self-tuning chip. In the part, the RWD sends a control command to turn on and off the self-tuning function of a commercial self-tuning RFID chip. Due to the opening and closing process, the measurement environment remains unchanged. By performing differential (OOD) measurements on information such as link loss and phase, the power difference and phase difference can be obtained. The difference between the adjustment range of the auto-tuning function and the default value when the auto-tuning function is turned off is defined as the self-tuning range difference. The power difference, phase difference, and self-tuning difference form a three-dimensional vector (OOD parameter) that is independent of the measurement setup. The benefits of OOD parameters are as follows: 1) OOD parameters can support more sensed states than existing techniques using one-dimensional information. 2) OOD parameters is obtained by commercial self-tuning RFID chip. 3) The sensing robustness and power transfer are obtained by optimizing antenna layout. 4) A RFID water level sensor is designed, experimental results under different measurement settings demonstrate that the method achieves robust sensing without sacrificing communication performance in all sensing states.

2) RFID sensing method based on frequency hopping pattern comparison. Since the impedance of the chip changes nonlinearly with the received power level, the above multi-dimensional differential method needs to adjust the power for the tags one by one to make the tags work in a low-power linear region, and the RWD is less efficient when acquiring information from multiple RFID analog sensors. To overcome the inefficiencies of the data acquisition process, a sensing architecture by applying a channel hopping mechanism to differentially measure the communication underlying parameters, including RSSI, phase, and self-tuning values is proposed. This method transfers the influence of measurement settings to the relationship of measurement parameters to operating frequency. Then, sensor information is retrieved from the patterns of the measured parameters through a discrepancy analysis between offline and online cubes. This method is measurement setup independent and has the following advantages 1) It utilizes the channel hopping mechanism in commercial RWD and does not require additional hardware and software modifications or infrastructure. 2) It relaxes the assumption of constant chip impedance and facilitates efficient retrieval of information from multiple sensor tags. 3) It can run the RFID IC over a wide input power level. 4) It can acquire multiple sensor information and label recognition programs, and its data collection process is time-saving.

3) Power-oriented decoupling RFID sensing method. The concept translates the setup influences into the self-tuning RFID chip output and the slope of available power of RFID chip under multiple radiated power levels of RWD. The self-tuning RFID chip output, part of sensing indicator, is obtained at the optimal radiated power of RWD where the minimum Euclidean distance among different possible sensing states is maximized. This method is independent of the measurement setup and has the following advantages 1) It relies on RSSI and commercial self-tuning RFID chip. Comparing to using phase information, the RSSI could be obtained by using low-cost RWD hardware. 2) It executes sensing operation at the optimal power level to improve sensing robustness. 3) It can operate over the full power level range of the RFID ICs. 4) It achieves a good balance of accuracy and efficiency.

4) The urban sewage system is related to the health of residents. RFID tags are used to detect the water level inside (PVC) pipes, which provides a cost-effective PVC pipe blockage detection system. Due to the dispersed nature of PVC pipes, proposed system can greatly reduce installation and maintenance costs. When blockages and leaks occur, efficient troubleshooting can be carried out by means of mobile RFID handheld RWD. The PVC pipe blockage monitoring and detection system shows the characteristics of passive, easy deployment and low cost. The proposed techniques has the potential to realize sustainable communication of massive IoT devices in smart cities and smart factories.

    Research areas

  • UHF RFID technology, Antenna sensor, Setup-independent, RFID-based sensors