The Research On Designing RFID Sensor

In recent years, the research of RFID has been developing much rapidly, and has been used and applied in every area in people’s everyday life, such as logistics, storage, library management, and so forth. In the meantime, there has been an increasing effort toward combining RFID technology and other technology, in order to achieve more innovative applications. Since UHF RFID tag is passive(no battery), wireless, in-expensive, etc., the combination of RFID and sensing technology, i.e. the possibility of using passive RFID tag as sensor attracts more and more interests by researchers in RFID applications.The rationale of using passive RFID tag as sensor is, RFID tag is usually labeled on the surface of the object or inside it, and the physical or chemical change of the material to which the tag is attached and the ambient environment can affect the tag, e.g. the tag’s impedance or gain would change. Thus we can use this variation of tag’s impedance or gain to reflect the physical or chemical change that we want to observe and realize remote-sensing. However, the difficulty of designing this kind of device is, the capabilities of communication and sensing demand opposite requirements, because we want the variation of the tag’s impedance or gain to be as big as possible to reflect the change of the progress we observe, but if we do so, the capability of communication will definitely degrade.Thus, the key problems are how to understand the relationship and paradox between the capabilities of communication and sensing of RFID sensor, how to define and quantify the capabilities of communication and sensing, how predict the theoretical max limits of the capabilities of communication and sensing, and how to choose an appropriate tradeoff in designing which meets the requirements of the capabilities of communication and sensing both. And this paper will present the analysis and design procedures in detail, and introduce an analysis method using iso-lines in normalized antenna impedance coordinate to analyze easily-and visually. And also, a discussion about how to use HFSS and Matlab associated with Genetic Algorithm to co-design, analyze and optimize the RFID sensor intelligently is given. In the end, a model of RFID sensor is introduced which detects the change of material height in a container, and it will be fabricated and measured to verify the theory.