Deformation and position of acoustically levitated liquid drops

A new numerical method has been developed for studying the static deformation of an acoustically levitated liquid drop in air. After the Fourier transformation is applied to the original integral form of the Helmholtz formula for the scattering of an axisymmetric acoustic wave by an incompressible liquid drop, solutions which are valid for all degrees of axisymmetric deformation up to the point of drop break-up are obtained. Calculations are presented for drops in both gravity and gravity-free environments, and are found to be in good agreement with experimental measurements by others. A physical picture of the competing processes introduced by drop deformation in a sound field is also presented. The predictions for the 1g case can be applied to ground-based experiments in which surface properties of acoustically levitated drops are being measured.