Passive radio frequency identification (RFID) tag has been shown efficient in item tracking and management in the supply chain. Attracted to low weight and small size of wireless nodes, some research work was conducted to extend the RFID advantage into environmental sensing applications. The concept is to using tag frequencies as sensing parameters. When variation occurs in the surrounding environment, such as temperature and humidity level, the operation frequencies of tags would be shifted, and such shift can be used to identify the degree of variation in the environment. One challenge of RFID tag is the distortion from other surrounding objects, the existence of obstacles and metals can have greatly impact on the sensing performance in both accuracy and sensing range. This thesis work conducts an investigation of the performance of a passive radio-frequency identification (RFID) based system. The investigation systematically probed the effects of passive RFID tag orientation and obstacles (blocking line-of-sight between a reader and a tag) as well as reading period (the time required for successful detection) on the range of detection. In the absence of obstacles, optimized tag orientation improved the system reliability and range of detection. At a reading distance where tag readability became unstable, increasing the reading period led to a higher reliability. A theoretical model was also established and was in good agreement with measurement results, providing a simple guideline to the further experiments. This work would also advance the knowledge understanding on wireless sensing on metal effect, humidity and temperature.

Passive radio frequency identification (RFID) tag has been shown efficient in item tracking and management in the supply chain. Attracted to low weight and small size of wireless nodes, some research work was conducted to extend the RFID advantage into environmental sensing applications. The concept is to using tag frequencies as sensing parameters. When variation occurs in the surrounding environment, such as temperature and humidity level, the operation frequencies of tags would be shifted, and such shift can be used to identify the degree of variation in the environment. One challenge of RFID tag is the distortion from other surrounding objects, the existence of obstacles and metals can have greatly impact on the sensing performance in both accuracy and sensing range. This thesis work conducts an investigation of the performance of a passive radio-frequency identification (RFID) based system. The investigation systematically probed the effects of passive RFID tag orientation and obstacles (blocking line-of-sight between a reader and a tag) as well as reading period (the time required for successful detection) on the range of detection. In the absence of obstacles, optimized tag orientation improved the system reliability and range of detection. At a reading distance where tag readability became unstable, increasing the reading period led to a higher reliability. A theoretical model was also established and was in good agreement with measurement results, providing a simple guideline to the further experiments. This work would also advance the knowledge understanding on wireless sensing on metal effect, humidity and temperature.

No / Abstract: Radio Frequency Identification (RFID) systems has gained increasing popularity with multiple deployments to existing wireless sensors in a view to achieve energy and overall operational efficiency at a much lower cost. This paper presents the design and analysis of a UHF (860-868MHZ) passive tag using HFSS (High Frequency Structural Simulator) platform. It explores specific tag geometry characteristics that affect overall tag antenna performance and presents the optimised result. The simulation results and parametric analysis are compared. Further simulations on HFSS platform is carried out to theoretically demonstrate the reflections of the tag when deployed as sensors to multiple levels of a cistern.

The project deals with a theoretical design of passive ultra-high frequency radio identification (UHF RFID) tag for the measurement of liquid levels. Liquid level has an influence on the input impedance of an RFID tag antenna. The changes of input impedance have been used to distinguish individual liquid levels. Furthermore, this project presents optimization methods for the highest efficiency of an UHF RFID tag in Matlab and it aims to design a suitable antenna within CST MICROWAVE STUDIO.