Waveshape distortion of high frequency acoustic waves in gas media

Abstract

In molecular dynamics simulations of an acoustic domain excited by a sinusoidally oscillating plane acoustic source in the frequency range of hundreds of megahertz, the density and velocity perturbations adjacent to the source are observed to be non-sinusoidal in shape. This distortion in the shape of the waves is investigated using a number of simulations of frequencies in the hundred of megahertz range and velocities up to 0.50 Å/ps. The relative distortion of the wave shape is characterised by a developed nested trigonometric function. The distortion is shown to be a function of the Mach number of the acoustic source rather than the source velocity amplitude. Trends in the distortion with source amplitude and frequency indicate that distortion of the velocity and density are independent of frequency. It is shown that the density and velocity perturbation can be approximated for any sound source Mach number within the range examined using the parametrised developed equation. The developed approximation could be used to accurately simulate the influence of an oscillating plane using a stationary analytical source. This could be used to develop a hybrid molecular/continuum model that will allow lower frequency simulations. The improved understanding of the causes of the distorted high frequency waveshape could also improve the fidelity of parametric arrays.