Effective T-matrix of a cylinder filled with a random 2 dimensional particulate

TL;DR

This paper derives an effective T-matrix for a cylinder filled with random 2D particles, enabling simplified modeling of multiple scattering of scalar waves like sound or light within such structures.

Contribution

It introduces a first-principles method to compute the effective T-matrix for a 2D particulate-filled cylinder, including ensemble averaging and validation through Monte Carlo simulations.

Findings

Effective T-matrix accurately describes scattering across frequencies.

Simplification to a homogeneous cylinder with an effective wavenumber for monopole particles.

Theoretical predictions match numerical simulations well.

Abstract

When a wave, such as sound or light, scatters within a densely packed particulate, it can be rescattered many times between the particles, which is called multiple scattering. Multiple scattering can be unavoidable when: trying to use sound waves to measure a dense particulate, such as a composite with reinforcing fibers. Here we solve from first principles multiple scattering of scalar waves, including acoustic, for any frequency from a set of 2D particles confined in a circular area. This case has not been solved yet, and its solution is important to perform numerical validation, as particles within a cylinder require only a finite number of particles to perform direct numerical simulations. The method we use involves ensemble averaging over particle configurations, which leads us to deduce an effective T-matrix for the whole cylinder, which can be used to easily describe the scattering from any incident wave. In the specific case when the particles are monopole scatters, the expression of this effective T-matrix simplifies and reduces to the T-matrix of a homogeneous cylinder with an effective wavenumber $k_\star$. To validate our theoretical predictions we develop an efficient Monte Carlo method and conclude that our theoretical predictions are highly accurate for a broad range of frequencies.