Research On Detection Mechanism And Application Of Differential Coil Eddy Current Sensor

Eddy current testing is a branch of non-destructive testing that has been popular in recent years,and this research has enabled large-area,fast,and high-resolution detection of conductors.This paper mainly focuses on the detection and study of surface cracks in pipelines,proposes a differential eddy current testing scheme,designs and develops array coil eddy current sensors,and conducts quantitative identification studies on microcracks.The main research content is as follows:(1)A rectangle-based coil eddy current sensor scheme is proposed,which is designed as a differential coil eddy current sensor.The working principle of the model is analyzed in depth based on mathematical and electromagnetic field theory.The analysis shows that due to the field-strength superposition effect,the differential coil eddy current sensor based on the rectangular pattern can induce greater magnetic induction,so the sensor will have stronger turbulence disturbance when it encounters a crack defect in the conductor.(2)The eddy current non-destructive testing technology is used to obtain the data of conductor defects,and the simulation results of the differential excitation and differential measurement eddy current sensors are compared.The working principle of the differential eddy current sensor is studied.Two kinds of micro-structured differential sensors are designed.The numerical simulation of the two sensor probes is performed by COMSOL electromagnetic field finite element simulation analysis software to study the sensitivity of the two sensors.The simulation results show that the output signal and sensitivity of differential excitation is stronger than the differential measurement,and the differential excitation sensor has a very high sensitivity.(3)An array eddy current detection scheme is proposed.A systematic research on an independently researched and developed array eddy current testing device is conducted,and the electromagnetic theory basis of its working principle is thoroughly studied.Numerical simulation research and analysis are also conducted.The simulation results predict that the array eddy current sensor can quickly and effectively determine the shape of cracks on the conductor surface,which can guide the evaluation of crack defects in reality.(4)Based on the differential excitation coil eddy current testing technology,a set of sensitive inner surface eddy current testing device for cracks on the inner surface of the pipeline is developed.The overall scheme utilizes the principle of differential excitation eddy current testing technology to specifically design the array eddy current sensor.As a circumferential three-dimensional model,the design circuit is a multi-channel relay switch control,and then combined with computer technology to carry out signal processing.The experimental results show that the detection system developed by the array on the micro-cracks in the pipeline surface has reliable detection performance.(5)Aiming at the difficult problem of crack quantitative identification technology,a method for quantitative identification of micro-cracks in eddy current non-destructive testing is proposed.In this study,the magnetic dipole model is used to calculate the eddy current signal,then the eigenvalues are extracted and the principal component analysis is used to reduce the dimension of a large number of feature information.The size of micro-crack defects can be quantified with the artificial intelligence algorithm.The results of the analysis show that this method is feasible.