Study Of UHF RFID Tag Design Method Based On Chip Characterization

Radio Frequency Identification(RFID)is a critical technology to achieve the Internet of Things(IoT).Among the existing solutions,passive Ultra High Frequency(UHF)RFID technology has attracted widespread attention due to its advantages such as high rate,fast response,and large operating range.Tag performance is a key factor that determines the performance of the RFID system.This thesis focuses on the design method of UHF RFID tags based on the measured values of chip characteristics and investigates four aspects of passive UHF RFID tags:analysis and design,chip characterization,antenna characterization,and temperature-sensitive characteristics of passive UHF temperature-sensing tags.A high-redundancy robust tag antenna impedance selection strategy is proposed and verified;two novel tag chip characterization methods are presented,which are wired and wireless methods,respectively;a simple and effective wired method for measuring balanced tag antenna impedance is proposed and validated;the temperature-sensitive characteristics of passive UHF temperature-sensing tags are studied,and the design principles of temperature-sensitive tag antennas that conform to the characteristics are proposed and verified.The main research work of this thesis is as follows:1.Systematically summarized the analysis methods for passive UHF RFID tags,the design criteria of the tags,and impedance matching strategies between antenna and chip.A high-redundancy robust tag antenna impedance selection strategy is proposed and verified based on the existing UHF RFID tag antenna design guidelines.2.The key to tag antenna design is to know the characteristics of the used chip.Recently,the continuous emergence of novel RFID tags has put forward new requirements for tag design.More comprehensive chip characteristic information must be obtained through measurement,including the chip sensitivity,the absorption state impedance,and reflection state impedance as a function of input power and operating frequency.The challenge is how to characterize the UHF RFID tag chip while ensuring that it is active.A two-channel wired measurement method is proposed to solve this problem.Compared with existing methods,the proposed method has a simple architecture,low operational complexity,easy implementation,and relatively accurate results.In addition to wired methods,the chip characteristics can also be measured by wireless methods.In this thesis,the existing wireless methods are classified into scalar and vector methods.Problems with the existing wireless measurement methods:the scalar method requires at least three tag antennas with different impedances,and need to know the respective antenna impedance,gain,and other parameters,data processing is also complicated;the vector method is more complex and instrument requirements are higher.In response to the above problems,a novel wireless measurement method for characterizing the absorption state impedance of UHF RFID tag chips based on vector backscattering signals is proposed and the effectiveness of the method is experimentally verified.3.Accurate characterization of the tag antenna is an indispensable part of the tag design and verification process.Existing methods of measuring tag antenna impedance require high calibration accuracy of the measuring equipment,cumbersome measurement processes,and data post-processing to obtain final results.In response to this problem,this thesis proposes and verifies a simple method to directly measure the impedance of a symmetrically balanced tag antenna.The proposed method only uses a single port of the vector network analyzer.Through a 180°Hybrid,two semi-rigid coaxial cables and a customized calibration process,it can realize the visual display of the tag antenna impedance without data post-processing.By comparing the results with those obtained by simulation and other classical measurement methods,it is clear that the proposed method is accurate and valid.4.To address the problem that the performance of the novel integrated sensing chip-type passive UHF RFID sensor tag fluctuates widely under different environmental conditions,typical passive UHF temperature-sensing tags were selected and studied.The temperature-sensitive characteristics of the UHF RFID temperature-sensing chip and the passive wireless temperature-sensing tag based on the chip were investigated.Three engineering tests were conducted:wired measurement of temperature-sensing chips with matching networks,wireless measurement of anti-metal tags with ceramic substrate patch antennas,and wireless measurement of dipole tags with different impedances.The corresponding experimental design scheme,system setup,test procedures,and measurement results are given.The results show that as the temperature rises,the real part of the temperature-sensitive chip impedance increases and the absolute value of the imaginary part decreases,which is consistent with the simulation data.Based on this,a design principle of the temperature-sensing tag antenna adapted to the temperature-sensitive characteristics is proposed,and the feasibility and effectiveness of the design principle are verified by experiments.The comprehensive performance of temperature-sensitive tag designed for high-temperature conditions is better than that designed only for normal temperature conditions in a wide temperature range.Engineering testing and analysis provide a reference for the design of robust temperature sensing tags over a wide temperature range.