Acoustic levitation of drops in air

The nonlinear interaction between an acoustic field and an inclusion possessing acoustic properties that are different from the host medium can, among other effects, yield a net body force on the inclusion. If the vertical component of the field gradient is sufficient (i.e., that of a standing wave) and its amplitude large enough, the force of gravity can be balanced—an effect commonly known as ‘‘acoustic levitation.’’ Acoustic levitation has been used in a wide variety of scientific studies, among them studies of sonoluminescing bubbles and investigations of liquid drop dynamics and surface rheology. A monofrequency air levitator will be demonstrated, and several aspects of drop physics will be illustrated by acoustically manipulating the drops. [Work supported by NASA.]