Probing density waves in fluidized granular media with diffusing-wave spectroscopy

TL;DR

This paper develops a model for analyzing how density waves influence diffusing-wave spectroscopy measurements in fluidized granular media, enabling better characterization of microscopic particle motions and heterogeneities.

Contribution

The paper derives a new form of the intensity autocorrelation function accounting for density waves, validated with experimental data from a gas-fluidized bed.

Findings

Model accurately predicts the impact of density waves on IACF

Separates contributions of density waves and microscopic scatterer motion

Enables characterization of heterogeneities in fluidized granular media

Abstract

Density waves are characteristic for fluidized beds and affect measurements on liquid-like dynamics in fluidized granular media. Here, the intensity autocorrelation function as obtainable with diffusing-wave spectroscopy is derived in the presence of density waves. The predictions by the derived form of the IACF match experimental observations from a gas-fluidized bed. The model suggests separability of the contribution from density waves from the contribution by microscopic scatterer displacement to the decay of correlation, thus paves the way for characterizing microscopic particle motions using diffusing-wave spectroscopy as well as heterogeneities in fluidized granular media.