  It is well known that acoustic fields can produce forces on single particles,
however they can also induce inter-particle forces due to multiple scattering
events. This multi-particle force -- here referred to as acoustic binding -- is
comparable to other acoustic forces when the particles are of order wavelength
in diameter. In principle, this force could be used as a tunable method for
directing the assembly of particles of mm-scales, but has not been extensively
explored in previous work. Here, we use a novel numerical method to compute
binding interactions between strongly scattering bodies and find that they can
produce stable clusters of particles with approximately wavelength separation.
Moreover, we also observe that -- depending on the level of damping -- these
structures can produce driven linear, rotational, or vibrational motion. These
effects are a result of the non-conservative and non-pairwise nature of the
acoustic binding force, and represent novel contactless manipulation and
transport methods with potential application to metamaterial synthesis and drug
delivery.
