Research On Deep Defect Of Plate Conductors Based On Eddy Current Nondestructive Testing

The eddy current detection of deep defects in flat conductors has a good application prospect.It has the advantages of rapid detection,high detection sensitivity,easy operation,and easy evaluation.It has important research value for the detection and evaluation of conductive materials.Based on the research dynamics of eddy current testing at our country and abroad,this paper combines the research methods of finite element simulation and experimental verification,and studies the influence of excitation frequency,probe size and probe structure on the reflection and transmission eddy current testing effects,based on this,the realization method of far field eddy current testing of flat conductor is studied.the main contents and innovations of the research are as follows:First,the detection mechanism of eddy current testing technology was analyzed.Based on the theoretical basis of electromagnetism,the basic theoretical equations for the analysis of eddy current problems are derived.The detection mechanism of reflection eddy current testing technology,transmission eddy current testing technology and remote field eddy current testing technology was analyzed.Second,parameters optimization of reflection and transmission eddy current probes.The excitation frequency,the coil size of eddy current testing,and the relative position of the excitation coil and the detection coil are the main factors affecting the performance of the eddy current sensor.For ferromagnetic and non-ferromagnetic plates,the effects of excitation frequency and probe size on amplitude,phase sensitivity and monotonicity of eddy current detection response signal were studied;the relationship between the detectable defect depth and standard eddy current penetration depth at different excitation frequencies was studied.The eddy current detection effect of the reflection eddy current(the excitation coil is coaxial and parallel to the detection coil)and the transmission eddy current(the excitation coil and the detection coil are coaxial but located on both sides of the tested flat conductor)are contrastively analyzed.Then,structure optimization of remote field eddy current testing probe for flat conductor.The magnetic shielding structure is the key influencing factor of remote field eddy current detection technology for flat conductors.The energy flow situation and the variation trend of the amplitude and phase characteristic curves in finite element simulation models with different thicknesses and high permeability magnetic shields are analyzed.According to the energy flow density map of the magnetic shield simulation model with different thicknesses and the certain thickness of the magnetic shield,the remote field eddy current effect of the flat conductor can be achieved,and the remote field eddy current probe structure of the ferromagnetic plate testing can be optimized.A remote field eddy current testing experiment platform was set up.The remote field eddy current probe was used to detect the amplitude and phase of the response signal for the subsurface defects testing with different heights of the ferromagnetic plate,which verified the reliability of the simulation analysis.Last,eddy current detection system design based on lock-in amplifier.Based on the working principle of the lock-in amplifier and the processing requirements of the eddy current detection response signal,a simple phase-sensitive detection circuit that can be used for eddy current detection response signal processing is designed.The eddy current detection platform based on the lock-in amplifier was set up based on the designed circuit and the existing laboratory equipment.