Identification of guided Lamb wave modes in thin metal plates using water path corrected frequency - wavenumber [f-k] analysis

Acoustic microscopy is widely used for the material characterization of thin plates having thicknesses < 100 mu m. For thin plate material characterization, the acoustic microscopy-based approach utilizes the guided Lamb wave modes generated in the plates by defocusing a single high-frequency focused transducer. Identification of the guided wave modes is vital in material characterization. Frequency-wavenumber analysis using 2D-FFT is commonly used to identify guided wave modes. In PVDF-based focused transducers used in acoustic microscopy, edge waves originating from the transducer rim influence the generation of guided waves, making the conventional frequency-wavenumber analysis erroneous. This study proposes a new water path corrected frequency-wavenumber (f-k) analysis using 2D-FFT to overcome the challenges imparted by the edge waves. In this approach, the water path of the Lamb wave modes is calculated and removed from the waveforms before performing 2D-FFT. The proposed approach has been demonstrated on thin metal plates of Aluminum, Copper and Brass having thicknesses of 45 mu m, 52 mu m and 52 mu m, respectively. A good correlation is obtained between theoretical and experimental results.