Research On Printable Chipless RFID Humidity Sensor

RFID technology is an emerging wireless technology,which is used for automatic identification,tracking,monitoring,logistics management and other fields.However,it is difficult to make IC RFID tags on a large scale due to its high cost.Printable chipless RFID humidity sensor prints the sensor on a flexible substrate through inkjet printing technology,which can effectively reduce the cost of the tag,and promote the widespread use of sensor.In this thesis,the paper substrate sensor with high quality factor and flexible substrate sensor loaded with humidity sensitive material PVA were designed and realized by means of genetic algorithm and HFSS software co-simulation.The content of this thesis is divided into four parts:(1)The principle of SRR and the distributed loading technique of SRR were deeply studied.Through the joint simulation of genetic algorithm and HFSS software,distributed loading was carried out inside the conventional SRR,and the resonance frequency and quality factor were optimized through simulation.Paper based resonator with good resonance characteristics and 2.45 GHz resonance frequency was designed.The problem of large dielectric loss and low resonance performance of the paper substrate was solved and the resonance characteristic of the sensor structure was improved effectively.(2)Using ink-jet printing technology to produce kodak photo paper and both-sided coated paper based humidity sensors.Kodak based sensor is highly sensitive and reaches 8MHz/%RH in high humidity range.The sensitivity curves of the both-side coated paper based sensor is approximately linear,and can be completely recovered after 2min with a recovery degree of 100%.The consistency of the two sensors is high,which is rarely affected by temperature.(3)The structure of the flexible humidity sensors loaded with the sensitive material PVA were designed by the joint simulation method of genetic algorithm and HFSS.The simulation study on the influence of process parameters on the sensor performance provides a theoretical basis for the setting of process parameters when the sensor is printed.The humidity sensitivity of pure PVA sensor,PVA polyimide sensor and PVA paper based sensor was studied by simulation.The feasibility of using the substrate and PVA to improve the sensitivity of the sensor was proved theoretically.(4)Flexible chipless RFID humidity sensors were fabricated by loading different concentrations of PVA on the surface of flexible substrate resonators.Test results show that: The sensitivity of pure PVA sensor is higher,and the sensitivity of high range humidity is obviously higher than that of low range humidity.The high range humidity sensitivity is the highest when the concentration is 15%,reached 9.44MHz/%RH,however,the recovery is poor.The sensitivity of PVA polyimide sensor is slightly higher than that of pure PVA sensor,and the highest sensitivity is 10MHz/%RH.The high range humidity sensitivity of both-side coated art PVA sensor can reach 12.22MHz/%RH,which is much higher than that of pure paper and pure PVA sensitive sensor.At the same time,the recovery performance is also improved compared with pure PVA sensor.The experimental results show that: Combining the humidity sensitivity of PVA with the humidity sensitivity of the paper substrate can improve the sensor performance to some extent.The printable chipless RFID humidity sensor studied in this paper has the advantages of low cost,simple structure,high humidity sensitivity,high recovery speed,flexibility,flexibility and large amount of preparation.Compared with other literatures,the sensitivity and recovery performance have been greatly improved,which is conducive to the promotion and use of intelligent packaging in logistics,transportation and other fields.