Dynamic coherent backscattering of ultrasound in three-dimensional strongly-scattering media

TL;DR

This study measures the diffusion coefficient of ultrasound in 3D strongly scattering media using dynamic coherent backscattering, extending existing theory to 3D and providing precise experimental results.

Contribution

The paper extends the microscopic theory of coherent backscattering to three-dimensional media and accurately measures the ultrasound diffusion coefficient in strongly scattering 3D disordered samples.

Findings

Diffusion coefficient D is approximately 0.74 mm^2/μs.

The diffusion process is slow, indicating low energy velocity.

The theory matches experimental data well in the diffuse regime.

Abstract

We present measurements of the diffusion coefficient of ultrasound in strongly scattering three-dimensional (3D) disordered media using the dynamic coherent backscattering (CBS) effect. Our experiments measure the CBS of ultrasonic waves using a transducer array placed in the far-field of a 3D slab sample of brazed aluminum beads surrounded by vacuum. We extend to 3D media the general microscopic theory of CBS that was developed initially for acoustic waves in 2D. This theory is valid in the strong scattering, but still diffuse, regime that is realized in our sample, and is evaluated in the diffuse far field limit encountered in our experiments. By comparing our theory with the experimental data, we obtain an accurate measurement of the diffusion coefficient of ultrasound in our sample. We find that the value of $D$ is quite small, $0.74 \pm 0.03$ mm$^2/\mu$s, and comment on the implications of this slow transport for the energy velocity.