Improved PCA Reconstruction-Based Unsupervised Anomaly Detection in Uncontrolled Structural Health Monitoring With Correntropy

Guided wave-based structural health monitoring is extensively utilized in various industrial applications to ensure the integrity of components within industrial systems. Among these monitoring techniques, principal component analysis (PCA) reconstruction methods are widely used for anomaly detection due to their computational efficiency and interoperability. However, existing PCA reconstruction methods are semisupervised anomaly detection approaches that require training on historical normal data and fail to detect anomalous signals within the training set. To address this limitation, this work proposes a correntropy PCA (C-PCA), enabling fully unsupervised anomaly detection on raw training data without requiring label information, when the dataset contains a high proportion of abnormal signals. This method allows anomaly detection on real-time measurements without the need for precleaned historical normal data or can also be used to generate clean data for existing semisupervised anomaly detection methods. In correntropy PCA, principal components are extracted from the correntropy matrix rather than the correlation matrix. The correntropy, representing the statistical dependence between samples of guided waves, is estimated utilizing a Gaussian kernel with a specified kernel width. Through the optimization of the kernel width, the correntropy PCA reconstruction method demonstrates superior anomaly detection performance compared with the standard PCA reconstruction method, especially in scenarios where training data are contaminated by a significant proportion of abnormal signals. Guidelines for the optimization of the kernel width are provided. The effectiveness of the correntropy PCA reconstruction-based anomaly detection method is validated using data collected from ten regions over an 80-day period, encompassing guided waves induced by damage occurring over durations ranging from 2 to 20 days.