Fundamental study of laser generation of narrowband Lamb waves using superimposed line sources technique

摘要

In this paper, a laser generated ultrasound technique called superimposed line sources is presented. The technique generates narrowband Lamb waves with a dominant wavelength by superimposing signals of line sources at the pitch corresponding to the desired wavelength. The superposition is performed in software after data are collected so that it permits flexibility of selecting the desired wavelength afterwards. By selecting the dominant wavelength in signals, signal complexity is reduced and the speeds and frequencies of wave modes with the selected wavelength can be determined through dispersion curves. Wavenumber-frequency domain filtering and continuous wavelet transform are used in this research to further reduce the complexity of the signals. Finally, simulations and experiments are conducted to investigate the defect detection ability of the technique. Reflection coefficients are calculated for fundamental AO and SO wave modes. Good agreement is found between the simulations and experiments and the result of coefficients with respect to defect and sample dimensions will be shown.