Non-Reciprocity in Acoustically Bound Clusters*

Intense acoustic fields can be used to create "acoustic traps", analogous to the better known optical trap. It turns out that if you have multiple particles in an acoustic field it will also create forces between particles due to multiple scattering effects. Recent work has shown that this 'acoustic binding' force is not pairwise, and that many body effects give rise to non-reciprocal driving forces. In this talk we will explore the assembly of 2D many particle clusters in the acoustic binding force through numerical simulations. We will show that small numbers of particles form spontaneously driven clusters, while larger confined systems assemble into a variety of ordered and disordered structures. In both cases, the observed behavior is strongly dependent on the ratio of particle size to acoustic wavelength, which controls the strength of the non-pairwise interactions.