Wireless Passive Tetile Strain Sensor Based On Technology

The wireless passive textile strain sensor based on UHF RFID(Ultra-high frequency radio frequency identification)technology combines RFID technology with textile materials to form a device with strain sensing function,which is suitable for long-term barrier-free monitoring in the field of military,urban security,agriculture,especially medical and health.At present,UHF RFID textile strain sensors have made great progress in the verification of structural principles.There are two ways to introduce RFID technology into textile strain sensors.One is to use the antenna or substrate of RFID tag as strain sensitive textile material,and the other is to integrate the textile components with strain sensing function into RFID textile label.Both methods solve the defects of high energy consumption and poor portability of traditional active wired strain measurement equipment.However,textile UHF RFID strain sensor is an emerging sensor technology in recent years,and further research is needed in the following aspects:(1)In terms of sensor characterization,the radio frequency parameters suitable for characterizing strain should be selected and optimized,comprehensively considering the sensor performance;(2)In terms of sensor performance evaluation,the sensitivity,linearity and reading distance of sensors are not only discussed,but also the repeatability of the sensor in practical application.The strain response characteristics of this type of sensor in the actual application environment,such as repeat stability,have not been discussed in depth.(3)In terms of the structure and preparation process of the antenna RFID strain sensor,there are few studies on the effect of the geometric structure parameters and preparation process of the strain sensing component on the performance and application limits,and the failure of the interconnection between chip and antenna have been less discussed.According to the above existing technical problems,this subject designed a strain sensor with an antenna hybrid RFID antenna structure(replacement of a part of the antenna conductor with a resistive strain sensitive yarn)to avoid the failure of the chip and the antenna due to mechanical action.This study also discussed the strain response characterization parameters of the sensor,performance evaluation indicators,the structural parameters of the strain sensitive yarn,the preparation process of the sensor and the sensitive yarn,and finally determined the structure and preparation of a full-fabric RFID antenna strain sensor which is suitable for flexible applications field.The specific research content and conclusions are as follows:(1)Using simulation technology,the influence of strain-sensitive yarn characteristics on the resonant frequency and return loss(S11)of the RFID antenna strain sensor is discussed parametrically,and the initial position,length and sensitivity range of the strain-sensitive yarn in the antenna as well as the most suitable sensor response parameters are compared and determined.First,the structure of the antenna strain sensor is designed,and the simulation model with the antenna hybrid RFID antenna tag is built.Then,different initial positions,lengths and sensitivities of strain-sensitive yarns as simulation parameters are used to numerical simulation.Besides,the resonant frequency and return loss of the RFID antenna strain sensor are obtained.After that,the sensitivity of the antenna hybrid RFID strain sensor is calculated,and the influence of the structural parameters of the strain-sensitive yarn on the sensing performance of the RFID antenna strain sensor is discussed.The results show that: in the sensor structure,the sensitivity of the RFID antenna strain sensor is related to the initial position of the strain sensitive yarn,because the current density distribution of the antenna is different.When the current density is high,the change of resistance and size has a great influence on the port impedance of the whole antenna,which cause the sensitivity of the RFID antenna strain sensor is high.With the increase of the initial length of the sensitive yarn,the sensitivity of the RFID antenna strain sensor generally shows an increasing trend,which is related to the geometry of the stretched antenna.The sensitivity of the RFID antenna strain sensor decreases with the increase of the strain sensitive yarn sensitivity.However,if the sensitivity of the strain sensitive yarn is too low,the RFID sensor response may not be sensitive to strains.In the discussion of response parameters,based on the analysis of anti-interference ability and response sensitivity,the resonant frequency of the antenna is the best response parameter.Subsequently,based on the strain sensor structure obtained from the simulation analysis,the corresponding RFID strain sensor is prepared,and the S11 minimum value and resonant frequency parameters are tested,and compared with the simulation results,to verify the rationality of the simulation,the designed structure and the proposed response parameters.(2)Through the discussion of strain-sensitive yarn preparation,elastic substrate selection,interconnection and hot-pressing process,a process plan for the preparation of a full-fabric RFID antenna strain sensor suitable for flexible applications is determined.This chapter first optimizes the preparation plan of strain-sensitive yarns and on this basis explores the number of cycles of the preparation process for preparing strain-sensitive yarns with the required sensitivity.Then,by comparing the elastic properties of the three elastic fabrics and the strain-sensitive yarns,an elastic substrate that can maximize the flexibility and flexibility of the strain-sensitive yarns is selected.Finally,the RFID antenna strain sensor is prepared through the interconnection and hot-pressing process according to the structure of the RFID strain sensor explored by the above simulation results.The results show that the optimized preparation scheme can produce strain-sensitive yarns with excellent electromechanical properties after two cycles;elastic fabrics with 20% spandex content best match the elastic properties of strain-sensitive yarns;the resistance of strain-sensitive yarns after interconnection only increases by 5 %,the slip degree of the interconnection point after stretching for 20 times is only 0.16%,which has a certain degree of mechanical reliability.The hot-pressing process not only satisfies the control of strain-sensitive yarns not moving freely,and benefits the mechanical and electrical stability of strain sensitive yarn but also the radiation performance of the strain sensors are not significantly affected.(3)Using the variable calibration method,the calibration curve of strain and backscatter power(RSSI)and resonance frequency are constructed,and the most suitable response parameters to characterize the strain is determined.Finally,the sensing performance of the prepared RFID antenna strain sensor is evaluated.In this paper,the RSSI and resonant frequency under 0-50% strain are firstly tested,and then a calibration curve of strain and RFID antenna strain sensor radiation performance is constructed.Response parameters with high fitting degree and good stability is selected as strain characterization indicators after testing the RSSI value and resonant frequency value under 35%strain to verify the calibration curve.Then,on this basis,the sensitivity,repeatability,and radiation performance of the RFID strain sensor are evaluated.The results show that the backscatter power is more suitable as an indicator of strain;the fabric-based embroidery RFID antenna strain sensor has better sensitivity,and the peak and zero points of the sensor repeatability decrease greatly with the increase of stretching times.However,because the drift trends are all linear,one-time function can be subtracted later to eliminate the trend.The radiation performance of the RFID strain sensor also stably and accurately reflects different strains,but there is a phenomenon that zero-point drift irregularly,which need to explore in the further.Based on the above discussion and analysis,this paper uses the structure of the antenna hybrid RFID antenna strain sensor to avoid the failure of the chip and the antenna due to mechanical action,and reveals the relationship between the strain-sensitive yarn structure parameters and the sensing performance of the RFID antenna strain sensor.A preparation process plan for a full-fabric RFID antenna strain sensor suitable for flexible applications is proposed,and the response parameters and sensing performance of the strain sensor are discussed and evaluated,which lays a foundation for the industrial preparation and application of this type of RFID strain sensor.In addition,it provides a new idea for the design of RFID strain sensors.