Dynamics of acoustically levitated disk samples

The acoustic levitation force on disk samples and the dynamics of large water drops in a planar standing wave are studied by solving the acoustic scattering problem through incorporating the boundary element method. The dependence of levitation force amplitude on the equivalent radius [Formula presented] of disks deviates seriously from the [Formula presented] law predicted by King’s theory, and a larger force can be obtained for thin disks. When the disk aspect ratio [Formula presented] is larger than a critical value [Formula presented] and the disk radius [Formula presented] is smaller than the critical value [Formula presented], the levitation force per unit volume of the sample will increase with the enlargement of the disk. The acoustic levitation force on thin-disk samples [Formula presented] can be formulated by the shape factor [Formula presented] when [Formula presented]. It is found experimentally that a necessary condition of the acoustic field for stable levitation of a large water drop is to adjust the reflector-emitter interval [Formula presented] slightly above the resonant interval [Formula presented]. The simulation shows that the drop is flattened and the central parts of its top and bottom surface become concave with the increase of sound pressure level, which agrees with the experimental observation. The main frequencies of the shape oscillation under different sound pressures are slightly larger than the Rayleigh frequency because of the large shape deformation. The simulated translational frequencies of the vertical vibration under normal gravity condition agree with the theoretical analysis.