Acoustic levitaton of air-filled shell-type materials

Standing wave acoustic levitation technique utilizes a standing wave formed between a sound source and a reflector. Nodes of the standing wave act as linear springs to attract the particles towards the pressure nodes, thus particles can be suspended or levitated in air. Theoretically, any material in any state can be levitated using this technique. However, in practice, the attempts to levitate materials are limited to those mostly of regular shape. A common type is air-filled closed form shell structures. These types of structures are often encountered as the likes of drug capsules. In this study, standing wave acoustic levitation of air-filled materials is performed. A number of hollow shapes in several sizes are manufactured on three-dimensional printers. The standing wave field in the presence of air-filled materials is predicted by computer simulations through finite element software for both a single-axis set-up and an annular set-up where levitation experiments are carried out. The prospect of levitating air-filled materials in a standing wave acoustic levitation set-up is evaluated and demonstrated.