The Study On Inner Laver Defect Detection In Multi-Laver Conductive Structures Using Pulsed Eddy Current Technique

The multi-layer conductive structures are widely used in the national economy. With the safety monitoring and security requirements of significant equipments becoming more and more important, improving the reliability of the detection system is extremely urgent. Pulsed eddy current testing technique is a relatively new electromagnetic nondestructive testing technology, which can improve the detection resluts of multi-layer structures. The article is mainly about the research on inner defect detection in multi-layer conductive structures, signal processing of pulsed eddy current transient response, and the development of detection system supported by the national natural science foundation of China. The experimental results show the developd system can improve detection capability for inner layer defects in multi-layer structures.The main work and innovation points of this thesis are as follows:1) The basis theory of pulsed eddy current testing has been researched based on the electromagnetic field theory and the finite element simulation, which provides a theoretical basis for the development of detection system. The feasibility of pulsed eddy current detection system is analized and verified.2) In order to improve the reliability of signal processing of pulsed eddy current transient response, the defect parameter identification method based on Fisher linear discriminant analysis (FLDA) has been proposed. The method using FLDA-based feature extraction combined with support vector machine can improve the results of defect parameter identification.3) The pulsed eddy current imaging technique has been studied and a defect edge extraction method using Canny edge detector has been proposed. The method can help to extract the edges of the pulsed eddy current imaging figure. The defect location and quantifying evaluation can be obtained based on the edge information.4) A pulsed eddy current C-scan detection system for multi-layer conductive structures has been developed and the hardware and software design has been improved.The experimental results have showed that the proposed methods using pulsed eddy current technique in this paper can help to improve the reliability of detection system. The research achievements have great significance for the nondestructive testing and evaluation of multi-layer structures.