Dynamics of acoustically bound particles

It is well known that scattering from acoustic fields can produce forces on single particles; however, they can also induce interparticle forces due to multiple scattering events. This multiparticle 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 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 viscous damping---these structures can produce driven linear, rotational, or vibrational motion. These effects are a result of the nonconservative and nonpairwise nature of the acoustic binding force and represent contactless manipulation and transport methods with a variety of potential applications.