Lamb Wave-Based Structural Damage Imaging Using a Time-Delay Weighted Three-Element TFM

Lamb wave-based imaging techniques play a vital role in structural health monitoring (SHM) for thin-walled structures. Nevertheless, the conventional Total Focusing Method (TFM) often relies on extensive transducer arrays, which increases system complexity and cost. To address this limitation, this paper proposes a three-element weighted total focusing method that enables high-quality damage imaging with minimal hardware. The method employs three transducers arranged in an equilateral triangle. The monitoring area is first segmented for preliminary damage localization by examining the time-delay signatures of the damage signals. A weighting factor, calculated from the mismatch between measured and theoretical distance differences, is subsequently incorporated to enhance the conventional TFM index. The final damage image is obtained by fusing all weighted information. Experimental verification on a T300/3231 carbon fiber reinforced polymer laminate plate demonstrates that the proposed method yields superior image clarity, a smaller spot size, and enhanced localization accuracy over the conventional TFM approach.