acoustotreams -- A Python package for acoustic-wave scattering based on the $T$-matrix method

Abstract

The transition-matrix ($T$-matrix) method has established itself as a prominent technique for computing the scattering response from spatially localized objects. The suitability becomes apparent particularly when considering not just isolated objects but also large ensembles of aperiodically or even periodically arranged objects. A versatile implementation of the method is provided by the treams program, which efficiently computes the electromagnetic response of scatterers in various arrangements [Comput. Phys. Commun. 297, p. 109076 (2024)]. Here, we rely on this framework and present a new program, acoustotreams, dedicated to simulating the acoustic scattering of pressure waves by clusters of particles, both with and without periodic boundary conditions. The computations are performed using the $T$-matrix method with scalar spherical and cylindrical waves as basis sets, and the scattering matrix ($S$-matrix) method in the basis of scalar plane waves for stratified media. The underlying theory is presented alongside the program structure and illustrative examples. The code is open-source and available on the Python Package Index for Linux, Windows, and macOS. Version control is maintained through GitHub, where we also provide automated tests, documentation, and detailed examples. We expect this work to contribute to the field of numerical methods for multiple-scattering problems by offering a computational framework capable of a comprehensive description of pressure-acoustic scattering in artificial media, including well-established metamaterials and metasurfaces.