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.

https://iopscience.iop.org/article/10.1143/JJAP.40.359/pdf

Rayleigh and Lamb Waves

Measurements of Multimode Leaky Lamb Waves Propagating in Metal Sheets

Dispersion curves, surface displacements, and displacement profiles over the plate thickness are numerically calculated for acoustic plate modes, propagating in fused and Y-rotated, X-cut quartz samples with thickness h/lambda in the range 0-4.5 (h, thickness; lambda, wavelength). The Anisimkin Jr.' modes with velocity vn close to that of longitudinal bulk wave vL and the dominant longitudinal displacement u1 distributed uniformly through the plate thickness are found in quartz crystals with cut angles mu = 120deg- 140deg and plate thickness h/lambda = 0-0.36, 0.94-1.78, 2.32- 3.08, and 3.64-4.44. The same modes in fused quartz are not found, except in a narrow region near zero thickness.

Properties of the Anisimkin Jr.' Modes in Quartz Plates

Coupling Efficiency Estimates for Acoustic Surface Wave Excitation with Piezoelectric Film Overlays

To achieve higher signal-to-noise ratios (SNRs) in imaging closed cracks in the vicinity of a surface, we propose a nonlinear surface-acoustic-wave phased array imaging method based on the fixed-voltage fundamental wave amplitude difference, which enables the inference of all the nonlinear components generated at cracks based on the energy movement between the fundamental and nonlinear components. After confirming its fundamental performance with a slit specimen, we applied it to two kinds of crack specimens: a thermal fatigue crack and a stress corrosion cracking extending from a mechanical fatigue crack. As a result, we succeeded in selectively visualizing the open and closed cracks with high SNRs. Furthermore, the analyses of delay-and-sum waveforms suggest that the proposed method can achieve a higher sensitivity than other nonlinear ultrasonic methods, which measure only a specific nonlinear component.

Rayleigh and Lamb Waves

Citations

Measurements of Multimode Leaky Lamb Waves Propagating in Metal Sheets

Properties of the Anisimkin Jr.' Modes in Quartz Plates

Coupling Efficiency Estimates for Acoustic Surface Wave Excitation with Piezoelectric Film Overlays

Nonlinear surface-acoustic-wave phased array with fixed-voltage fundamental wave amplitude difference for imaging closed cracks

Quasi-bulk Rayleigh waves in semi-infinite media of arbitrary anisotropy

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