Event-triggered passive–active guided wave monitoring for a PZT-embedded smart composite panel

Abstract

Composite structures are vulnerable to impact-induced local anomalies that are often difficult to detect visually, necessitating structural health monitoring (SHM) methods capable of both impact localization and post-impact assessment. This study proposes an event-triggered passive–active SHM framework for a piezoelectric transducers (PZT)-embedded smart composite panel. The embedded PZT array functions as a unified sensing and actuation network, enabling a continuous procedure of passive impact localization and active damage detection. A PZT-embedded smart composite panel was fabricated, and tensile tests were performed to verify the mechanical compatibility of the sensor integration scheme. In the passive stage, impact localization was achieved through continuous wavelet transform, first-peak extraction, Gaussian-windowed cross-correlation, and probabilistic imaging. In the active stage, two time–frequency features, the energy ratio (ER) and the normalized residual entropy (NRE), were extracted from differential guided-wave responses, and a Mahalanobis-distance (MD)-based indicator was constructed within a healthy reference space for state discrimination. Experimental results demonstrate that the passive method achieves high-accuracy impact localization. Furthermore, while ER characterizes the energy of damage-induced scattering waves, NRE provides complementary information regarding the temporal energy redistribution of the residual signals. By synthesizing ER and NRE, the proposed MD-based indicator is shown to effectively separate healthy and local-anomaly states. Compared with conventional damage indices, the proposed method more effectively suppresses healthy-state fluctuations and improves discrimination stability.