Application of Principle Component Analysis in hidden Corrosion Detection of Aircraft Multi-layered Structure with Pulsed Eddy Current

It's required to identify the defect signals from interfered signals caused by lift-off effect, and estimate the defect depth in aircraft multi-layered structure hidden corrosion detection with pulsed eddy current testing. A simulated sample of multi-layered riveted metal structure was made and different size and depth corrosion defects were tested. PCA was used and first three principal components were extracted. Results show that PCA method is able to distinguish pure lift-off signals against Signals with corrosion defects between the layers significantly. Pure lift-off signals were identified from pure corrosion signals and corrosion plus lift-off signals by applying K-means algorithm to the extracted principal components. But signals with both lift-off and corrosion components, can not be identified exactly from pure corrosions with PCA method.