Damage Imaging in Plate Structures Under Broadband Chirp Excitation Based on f-k Domain Modal Separation and Additive–Multiplicative Modal Fusion

Compared with conventional narrowband excitation, broadband chirp excitation covers a wider frequency range and can therefore provide richer damage-response information for plate structures. In this study, the application of a modal superposition imaging method based on frequency-wavenumber (f-k) domain modal separation and additive–multiplicative fusion under broadband chirp excitation was investigated through numerical simulations and experiments. First, the acquired signals were separated in the f-k domain, and the A₀ and S₀ modal responses were extracted, respectively. Subsequently, modal fusion imaging was implemented by fusing the imaging results of different modes through additive–multiplicative modal fusion. The results show that, within the selected frequency band, single-modal imaging can effectively characterize the damage location, whereas modal fusion can further reduce the damage region and improve the localization accuracy. Compared with time-domain common-source method (CSM) imaging, the f-k domain method can make fuller use of the effective frequency components within the selected frequency band and can account for guided-wave dispersion, thereby producing more compact imaging results while maintaining localization accuracy. These results verify the effectiveness of the proposed method under broadband chirp excitation and demonstrate its potential for multimodal damage identification.