Enhanced baseline-free damage imaging in composites via broadband adaptive-compensation multipath virtual time reversal method.

Baseline-free damage imaging is a promising approach for guided wave-based structural health monitoring of composite structures, but its performance under sparse actuator-receiver sensing configurations is often limited by insufficient path coverage and multipath-induced distortions. In composite materials, this problem becomes more challenging due to material anisotropy, which causes strong dispersion and uneven amplitude attenuation during wave propagation. To address this issue, a broadband adaptive-compensation multipath virtual time reversal (BAM-VTR) method is proposed. Boundary-reflected waves are utilized to form additional virtual sensing paths under a non-overlapping time-window constraint, improving spatial coverage without increasing the number of sensors. To account for the distortion resulted from anisotropic propagation, a multi-tone broadband excitation is used for system reconstruction, and an adaptive frequency-domain compensation strategy is introduced to correct phase distortion and amplitude imbalance among different paths. Experiments are conducted on a 1000 mm × 1000 mm carbon fiber reinforced polymer plate using a sparse hybrid network consisting of piezoelectric transducers and fiber Bragg grating sensors. The results show that the BAM-VTR method reduces reconstruction artifacts and improves the consistency of damage indices. Reliable damage localization is achieved for defects located in both central and boundary regions, with errors generally within 2 cm.