Investigation of 3D surface acoustic waves in granular media with 3-color digital holography

Abstract

This paper reports the implementation of digital color holography to investigate elastic waves propagating along a layer of a granular medium. The holographic setup provides simultaneous recording and measurement of the 3D dynamic displacement at the surface. Full-field measurements of the acoustic amplitude and phase at different excitation frequencies are obtained. It is shown that the experimental data can be used to obtain the dispersion curve of the modes propagating in this granular medium layer. The experimental dispersion curve and that obtained from a finite element modeling of the problem are found to be in good agreement. In addition, full-field images of the interaction of an acoustic wave guided in the granular layer with a buried object are also shown.

Acoustic Emissions of Nearly Steady and Uniform Granular Flows: A Proxy for Flow Dynamics and Velocity Fluctuations

“…We assume that (a) the elastic waves are generated during binary collisions between particles in adjacent layers, at speeds corresponding to the particles' fluctuation velocities, (b) collisions are described by the Hertz contact law and the radiated elastic energy is the work done by the impact force during the contact (Farin et al, 2015;Johnson, 1987), and (c) the acoustic waves propagate from the layer where they are generated down to the bottom of the channel. Attenuation in granular media is frequency dependent (Leclercq et al, 2017;Legland et al, 2012;Martin et al, 2018) and evolves with the reconfiguration of force chains during the flow (as illustrated by Lherminier et al (2014)), but for the sake of simplicity we assume here that attenuation with distance to the bottom is frequency independent, with constant attenuation coefficient γ g . Attenuation in granular media varies strongly, depending on the confining pressure, packing fraction, signal frequency, etc.…”

Micro/nano acoustofluidics: materials, phenomena, design, devices, and applications

“…Data from a high density of points can be obtained simultaneously using DH but, so far it lacks the ability to provide continuous (non-stroboscopic) measurements at frequencies greater than 1 MHz. Poittevin et al 84 provide a good introduction to the interested reader, and Leclercq et al 85 demonstrate the ability to simultaneously measure three dimensions of displacement in acoustic waves traveling in a solid using threecolor DH. Typically, particle tracking is accomplished by optical videography and particle image velocimetry (PIV), but Cacace et al 86 have applied DH to track particles in 3D that are moving under acoustophoresis.…”

Holographic measurement of surface acoustic wave parameters in crystals

“…Laser frequency multiplication additionally increases the sensitivity of measurements [6]. In fact it allows simultaneous SAW visualization across the entire surface [7] studied and direct measurement of wave parameters (wavelength, amplitude and oscillation pattern) [8,9]. However existing holographic measuring systems do not deliver the required time and spatial resolution for the visualization and parameter measurement of high-frequency ultralow amplitude oscillations generated by SAW [10].…”