Measurements of multimode leaky lamb waves propagating in metal sheets

In this paper, we present an experimental method for determining complicated dispersion relation of multiple modes of leaky Lamb waves propagating in a plate. The measurement system is based on a focused polyvinylidene fluoride (PVDF) transducer and its defocusing measurement method. A standard waveform processing procedure is developed to analyze the measured acoustic waveforms. With a new image representation method, the dispersion relation of the leaky Lamb wave is displayed as a gray-scale image. Multiple dispersion curves of leaky Lamb waves can be easily identified in the image and then quantitatively determined. Metal sheets of 0.2 to 0.5 mm in thickness are experimentally tested by this technique. Up to eight modes of leaky Lamb waves in the frequency range of 4 to 20 MHz are simultaneously excited and detected. The dispersion curves are accurately determined.