Defect classification using the pulsed alternating current field measurement technique based on the Smoothed Pseudo Wigner-Ville distribution and principal component analysis

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Introduction Pulsed Alternating Current Field Measurement (PACFM) has been proven to offer significant advantages in detecting surface and subsurface defects in structural components, and has been successfully applied to nondestructive testing of multilayer structures such as aircraft wings. Although pulsed excitation response signals carry rich time-domain and frequency-domain information, conventional methods that rely solely on a single time-domain feature are susceptible to noise interference, which may reduce detection accuracy and limit the ability to distinguish different defect types. Methods To overcome this limitation, this study employed the Smoothed Pseudo Wigner–Ville Distribution (SPWVD) to perform time–frequency analysis on the defect response signals, generating three dimensional time–frequency distribution maps that include time, frequency, and amplitude dimensions. Subsequently, Principal Component Analysis (PCA) was applied to reduce the dimensionality of the time–frequency results, eliminate redundant information, and extract the signal features characterized by the parameter ω 2 , which served as the key feature for defect identification and classification. Results Experiments were carried out on an aluminum plate with artificially machined defects of varying depths and positions. The results show that the extracted ω 2 signal features can accurately identify and distinguish both surface and subsurface defects, achieving clear classification under different defect conditions. Discussion The proposed strategy combining SPWVD with PCA effectively utilizes the joint time–frequency information of the pulsed responses, overcoming the noise sensitivity of single-domain features. The successful classification of surface and subsurface defects in the experiments indicates that this method provides a reliable technical means for inspecting multilayer structures.

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