Research On The Design Of High-sensitivity Passive RFID Sensor Tag

In recent years,passive radio-frequency identification(RFID)sensing technology,which integrates passive RFID technology and sensor functions,has attracted much attention.The major combinations of passive RFID technology and sensors are the combinations of RFID tags and sensors,viz.,passive RFID sensor tags.Passive RFID sensor tag has the advantages of low cost and long life.The design challenge of passive sensor tag is to achieve sensing sensitivity as high as possible for accurate sensing of small environmental changes.Common designs of passive RFID sensor tags were carried out by specifically selecting the tag antenna topology and optimizing its geometry.In this thesis,no matter which topology of tag antenna is selected or whether the tag antenna is optimized,a passive sensitivity booster can be designed and inserted between the RFID chip and tag antenna of sensor tag,to greatly improve the sensing sensitivity of passive RFID sensor tag.Focusing on the sensitivity booster,the research contents include:1.The network sensitivity theory of matching network is established.The definition of network sensitivity is proposed for matching network based on the theories of microwave network and impedance matching,and the network sensitivity for perfect matching and slight mismatching networks are analyzed.Several matching circuits are designed,fabricated and measured to demonstrate the validity of the definition and analyses of network sensitivity;2.The design theory and method of sensitivity booster are proposed.The input impedance of tag antenna changed versus environment generally defines a load variation path.Matching networks designed for different loads on that path will provide different overall sensitivities in the whole path.The one with the maximum overall sensitivity in the whole path is selected as the sensitivity booster.The design guide rules of sensitivity booster are proposed to determine its scattering parameter and the best load,and the realization methods of lumped and distributed sensitivity boosters are also given;3.The design of high-sensitivity passive RFID sensor tag based on sensitivity booster is studied.Common designs of passive RFID sensor tags improve the sensing sensitivity by optimizing the geometry of tag antennas with selected topologies.The design examples prove that,by inserting the sensitivity booster into optimized sensor tags,the sensing sensitivity can still be greatly improved.Since the antenna optimization is generally blind and time-consuming,the design examples demonstrate that the sensitivity booster can combine unoptimized tag antenna to efficiently design high-sensitivity passive RFID sensor tag.Considering the fact that the sensor position on tag antenna is an important factor affecting the sensor tag's sensitivity,the sensor position is optimized to maximize the sensitivity improvement caused by sensitivity booster.4.The collaborative optimization design of sensitivity booster and tag antenna is studied.First,to further achieve higher sensitivity,the most suitable optimization objective of tag antenna for sensitivity booster is proposed,with the help of tag antenna optimization based on the MOEA/D-DE(multi-objective evolutionary algorithm based on decomposition combined with differential evolution).Then,to achieve a more compact structure for high-sensitivity sensor tag,the integrated design of sensitivity booster and tag antenna is carefully considered.The necessity of integrated design is illustrated by analyzing the weight of sensitivity booster and tag antenna topology in high-sensitivity passive RFID sensor tag design.Finally,utilizing the MOEA/D-GO(MOEA/D combined with genetic operators)and fragment type structure to explore the most sensitive or suitable antenna topology for passive RFID sensor tag.In summary,through the systematically researches of the sensitivity booster,the author provides a brand new and more effective method for the design of high-sensitivity passive RFID sensor tag.