Research On Chipless Radio Frequency Cross Domain Sensing For Fruit And Vegetable Quality Status Detection

Chipless Radio Frequency Identification（CRFID）is widely used because of its light weight,reasonable price,universality and other advantages.CRFID tags have a theoretically unlimited life,eliminating the use of silicon chips and integrated circuits,and becoming an important medium for identification sensing.The combination of smart materials sensitive to a certain parameter or multiple parameters with coreless tags can achieve RF cross domain sensing functions.Taking fruit and vegetable quality detection as an example that can be detected and analyzed by measuring physical variables such as temperature and humidity as well as metabolic substances released by fruits and vegetables,such as carbon dioxide and oxygen concentration.Therefore,sensing temperature,humidity,gas and other index changes has wide application in the field of fruit and vegetable quality status detection.In this thesis,the research on CRFID technology in the field of detecting related factors of fruit and vegetable quality status is as follows:Firstly,the working principle of CRFID technology and coreless tag is discussed,the intelligent materials and sensing technology used in quality status detection are analyzed,and the integration of CRFID sensing technology and fruit and vegetable quality status detection technology is studied;a system and method for fruit and vegetable quality status detection is proposed,the detection of fruit and vegetable quality status is achieved by detecting the resonance offset and amplitude of RF signal.Second,CRFID tags based on split ring resonator（SRR）structures were designed,and a thin layer of sensitive material was established as a sensing unit for the tag.The sensing principle of the sensing tag was simulated using the sensing unit.When the sensor unit was sensitive to parameters,resulting in gradual changes in impedance,changes in conductivity affecting the resistance value would cause the amplitude and resonance offset of the tag,and the resonance and amplitude offset gradually increased or decreased as the resistance value changed.It provides a simulation experimental basis for detecting the humidity and carbon dioxide parameters caused by changes in the quality status of fruits and vegetables.According to simulation experiments,using screen printing technology to create physical tags,the agricultural Io T sensing monitoring system for tag sensitivity calibration and the coreless tag test system were built,and the resonance characteristics of the coreless tags were verified.The sensitivity of the coreless sensing tag was investigated based on the test system built,the tag was placed in the CO₂ and humidity test environments with a total resonance offset of 30 MHz and 16 MHz,respectively,with significant resonance offset,so the tag has good sensitivity to CO₂ and humidity changes.For fruit and vegetable quality state detection scenarios,three different types of fruits and vegetables were stored in the Agricultural Internet of Things sensor detection box,and the chipless sensing tags were used to detect the RF signal responses during different quality states.The results showed that fruits and vegetables with different quality states had different harmonic responses and amplitude offsets,and the resonance responses of different types of fruits and vegetables had sensitivity differences.The coreless sensing of different standard radio frequency signal responses can be used as a basis for analyzing and judging the quality status of fruits and vegetables,and as a reference index for detecting their quality status.