Bimodal Warped Frequency Transform (BWFT) for guided wave mode conversion characterization

Dispersive and multimodal guided wave propagation environments are often avoided in Structural Health Monitoring (SHM) applications by single mode selection through narrowband excitation and wavelength tuning. However, scatterer-induced mode conversions are relevant to damage localization and characterization. A Bimodal Warped Frequency Transform (BWFT) is proposed to track the time-frequency structure of propagating waves undergoing mode conversion in dual-mode environments. The BWFT provides a two-dimensional representation of a recorded time-trace in a modal distance vs. total distance domain. Consequent "modal path history" retrieval can effectively improve damage detection and characterization in broadband, multimodal regimes, as demonstrated both numerically and experimentally