Abstract
In this article, we describe the use of a continuous-wave laser scanning method to generate non-dispersive surface acoustic wavepackets, which propagate along the sample surface without any waveform change. To achieve this goal, a coated linear elastic film on a non-linear substrate allows for careful balancing of dispersion and non-linearity effects. The scanning speed of the laser source and the thickness of the coated film were parametrically investigated to determine the optimal scanning speed for the generation of ultrasound for a given thickness of the coated film. In the first step, four different combinations of scanning speeds and the thickness of the coated film are presented to illustrate the generation of the narrowband ultrasound. The purpose of the scanning laser source is to effectively generate large amplitude ultrasound that takes the material into the nonlinear range. Further optimization through a careful matching combination of the scanning speed and the thickness of the coated film, whereby the dispersion effect was compensated entirely by the non-linearity effect, was used to generate non-dispersive ultrasonic wavepackets, which subsequently propagate with little distortion. The main findings of the simulations indicate that non-dispersive surface acoustic wavepackets for coated systems can be generated via the scanning laser source approach for specific values of scanning speed and thickness of the coated film.
Highlights
Surface waves propagating on the shallow water constituted the first system in which solitary waves have been observed and studied,1 and they continue to play an important role in the field of nonlinear waves
To better understand the influence of the scanning speed factor, we focused on the former process, while the scanning speed was the only variant
Note that the spectrum of the generated wavepacket for the scanning speed of 2000 m/s showed the suppression of harmonic waves, and we investigated a range of speeds around this value
Summary
Surface waves propagating on the shallow water constituted the first system in which solitary waves have been observed and studied, and they continue to play an important role in the field of nonlinear waves. Pulsed laser generation provides unique possibilities to launch broadband ultrasonic waves.. Pulsed laser generation provides unique possibilities to launch broadband ultrasonic waves.9 With such an all-optical setup, solitary waves can be excited in a dispersive layered structure when the dispersion effect is balanced by nonlinearity. Lomonosov and Hess have investigated several aspects of solitary waves by laser ultrasonics.12,13 They observed solitary wave propagation in layered structures for normal and anomalous dispersion based on a laser-based technique for the contact-free generation and detection. We numerically investigate the thermoelastic generation of non-dispersive wavepackets in a nonlinear half-space with a thin linear elastic coating. We show that by appropriate scanning of a laser over a certain distance of generation, it is possible to generate wavepackets that are subsequently non-dispersive
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