Research And Design Of Long Range Chipless RFID Sensor

With the development of the Internet of Things,RFID technology is currently being widely used in more and more scenarios.RFID systems usually need to operate over a long reading range,and must be accurate and low-cost.Chip RFID tags support a longer reading range,but the cost is higher.In contrast,chipless RFID tags have become an effective solution to improve tag reliability and reduce costs.Because there is no chip,the tag transmits useful signals only by scattering the electromagnetic waves emitted by the reader,resulting in a short transmission range.Therefore,this paper focuses on the problem of chipless RFID long-range sensing.The main research issues include coding capacity,sensitivity,reading range,reliability,and so on.The main work and results of the paper are as follows:1.A long range chipless RFID humidity sensor with polarization conversion is proposed and designed,which can suppress the environment clutter.The sensor tag is designed on a double-sided copper-clad FR-4 substrate.The resonators of the top copper-clad etching tag include sensing resonator and coding resonators,and the bottom metal is used as the grounding plane.The coding unit and the sensing unit adopt the bent dumbbell-shaped strips and double spiral strip with polarization conversion respectively,which are used to minimize the influence of the surrounding environment on the tag response and improve the reliability of the sensor.The layer of PVA sensitive material is coated on the surface of sensing resonator effect the resonance frequency when environmental humidity changes,which realize the humidity sensing.The layout of the sensor tag is compact and suitable for building array to improve its radar cross section(RCS)for long range sensing.Simulation and measurement results show that the sensor can achieve a good humidity sensing at a reading range of 1.4 meters.The sensor shows pretty good performance and has a wide application prospect.2.A high sensitivity and long range humidity sensor based on square ring resonator coupled to interdigital electrodes(SRRCIE)is proposed and designed.The sensor is etched on a single-sided copper-clad PTFE substrate,which is composed of interdigital electrodes coupled inside the square ring resonator.The total size of the sensor unit is 25 mm×25 mm×1 mm.The square ring resonator ensures a high enough RCS response of the sensor tag,and the capacitance structure of interdigital electrode improves the sensitivity of the sensor.When the sensor tag is excited by plane wave,interdigital electrode will cause the square ring resonator RCS response to generate notch,and the notch depth of 20 d B can ensure that the tag can be easily detected.In order to realize humidity sensing,PVA is coated on the surface of sensor tag,which not only improves the sensitivity of sensor,but also simplifies the processing difficulty.Finally,the designed sensor tag array structure can significantly improve the radar cross section(RCS),and the 2×2 array sensor tag can achieve a reading range of 4.8 meters by calculation.The experimental results show that the designed sensor can realize the humidity sensing function with a sensitivity of 20MHz/% RH.3.A long range chipless RFID humidity sensor based on Van-Atta array is proposed and designed.Van-Atta array is a 1×2 linear array composed of two dual-polarized aperture-coupled microstrip antenna connected by two equal length transmission lines.The coding and sensing functions of sensor tag are realized by coupling three pairs of spiral resonators with different sizes inside two transmission lines of the binary linear array.In the working frequency band,the sensor tag generates three resonant frequencies,which correspond to one sensing resonant frequency and two coding resonant frequencies respectively.By loading a stub in the spiral resonator gap to control whether the sensor tag has a resonant frequency in the working frequency band,the sensor tag achieves a coding capacity of 2 bits.By opening a rectangular slot with the same size as the sensing unit on the upper substrate and injecting a certain amount of PVA liquid into the slot,the humidity sensing function with sensitivity of 3.15MHz/%RH is realized.Because of the retro-reflective property of Van-Atta array,that is,the reflected signal will return along the direction of the incoming wave,the sensor designed can realize long range signal transmission.The results show that the sensor tag has the retro-reflective characteristic of [-30°,30°] and can achieve a reading range of 3.5 meters.