Research On Chip-less RFID Metal Crack Sensor For Detecting Crack Width And Depth

Real-time monitoring of fatigue cracks in railways,bridges and pipelines is important for maintaining low cost,extending service life,and improving public safety.To achieve the goal of low-cost,real-time,non-contact measurement of sensors,chip-less RFID sensors have become a new method for crack monitoring.At present,the chip-less RFID metal crack sensor mainly has the following three problems.Firstly,conventional designs use a single resonance feature to detect crack width and direction,with low sensitivity and reliability.Secondly,sensors rarely address an important parameter in crack detection—crack depth.Finally,the metal crack multi-parameter sensor is realized by the combination of multiple resonators,so the structure is complicated.In order to solve the above problems,a high-sensitivity dual-polarization chip-less multi-modal RFID sensor is designed to realize the simultaneous detection of two parameters,the crack width and the crack direction.A chip-less RFID sensor with a single resonance structure is designed to meet the detection requirements of both the width and depth of metal cracks.The data separation algorithm is used to decouple the interaction between crack width and depth,and the crack width and depth data are extracted respectively.The research content is mainly divided into the following three parts.(1)A dual-polarized chip-less RFID sensor is designed based on an “ 工 ”-shaped resonator.In order to improve the sensitivity of the sensor,the resonance characteristics of resonators with different structures are compared,and the “工”-shaped resonator is selected as the initial structure of the sensor,which can realize omnidirectional detection of cracks.The loaded circular resonator was combined with it to achieve multi-mode sensing in the frequency range of 2GHz–6GHz,and the electromagnetic simulation software HFSS is utilized to optimize the structure and simulate the performance of the sensor.The sensitivity of crack width detection in 0°,45°,90°,and 135°directions is 43 MHz/0.1 mm,27.2 MHz/0.1mm,33 MHz/0.1 mm,and 28 MHz/0.1 mm,respectively,which greatly improves the sensitivity of the sensor.At the same time,the reliability of detecting the crack direction is improved by the dual-polarization detection method.(2)A chip-less RFID metal crack multi-parameter sensor with single resonance structure is designed.A candy-shaped resonator structure is obtained by combining a circular resonator and a square resonator,which is used to simultaneously detect the width and depth of cracks.Load cracks with different widths and depths for simulation analysis,obtain their frequency shift characteristics and amplitude characteristics,and fit their sensitivity curves.The obtained resonance frequency shift has a linear relationship with the crack width and depth,and the amplitude change has a quadratic relationship with the crack width and depth.It provides a data basis for the subsequent separation of crack width and depth parameters.(3)In the composite response of the sensor’s amplitude-frequency characteristics,the two-dimensional variables of crack width and depth are separated,through feature extraction and selection,and multiple feature fusion.Principal component analysis,BP neural network and GA-BP neural network models were used to separate and predict the crack width and depth,respectively.The network parameters are determined by comparing the average error value of multiple experiments to verify the network performance.The separation effect of each method was compared,and the GA-BP neural network model was finally selected for separation.The accuracy rate is 80%,which realizes the dual-parameter detection of crack width and depth by a single resonant structure.The chip-less RFID metal crack sensor studied in this paper can perform multi-parameter detection,which improves its sensitivity and reliability.It has broad application prospects in structural health monitoring.