title: Frequency Optimization for Enhancement of Surface Defect Classification Using the Eddy Current Technique.
abstract: Eddy current testing is quite a popular non-contact and cost-effective method for nondestructive evaluation of product quality and structural integrity. Excitation frequency is one of the key performance factors for defect characterization. In the literature, there are many interesting papers dealing with wide spectral content and optimal frequency in terms of detection sensitivity. However, research activity on frequency optimization with respect to characterization performances is lacking. In this paper, an investigation into optimum excitation frequency has been conducted to enhance surface defect classification performance. The influences of excitation frequency for a group of defects were revealed in terms of detection sensitivity, contrast between defect features, and classification accuracy using kernel principal component analysis (KPCA) and a support vector machine (SVM). It is observed that probe signals are the most sensitive on the whole for a group of defects when excitation frequency is set near the frequency at which maximum probe signals are retrieved for the largest defect. After the use of KPCA, the margins between the defect features are optimum from the perspective of the SVM, which adopts optimal hyperplanes for structure risk minimization. As a result, the best classification accuracy is obtained. The main contribution is that the influences of excitation frequency on defect characterization are interpreted, and experiment-based procedures are proposed to determine the optimal excitation frequency for a group of defects rather than a single defect with respect to optimal characterization performances.
authors.affiliation: School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, China. wuzhi3495@cumt.edu.cn.|Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou 221116, China. wuzhi3495@cumt.edu.cn.
authors.forename: Mengbao
authors.initials: M
authors.lastname: Fan
authors.affiliation: School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, China. wang501313823@126.com.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: School of Information and Electrical Engineering, China University of Mining and Technology, Xuzhou 221116, China. caobinghua@cumt.edu.cn.
authors.forename: Binghua
authors.initials: B
authors.lastname: Cao
authors.affiliation: Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China. yeripple@hotmail.com.
authors.forename: Bo
authors.initials: B
authors.lastname: Ye
authors.affiliation: School of Electrical and Electronic Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK. a.sunny@newcastle.ac.uk.
authors.forename: Ali Imam
authors.initials: AI
authors.lastname: Sunny
authors.affiliation: School of Electrical and Electronic Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK. g.y.tian@newcastle.ac.uk.
authors.forename: Guiyun
authors.initials: G
authors.lastname: Tian
keywords: defect classification; eddy current sensor; feature extraction; frequency optimization; nondestructive testing; probe response