Phase-shift expansions for approximate radiation forces on solid spheres in inviscid-acoustic standing waves.

Previously acoustic radiation forces on spheres have been expressed using scattering phase shifts associated with the corresponding traveling wave scattering situation. That approach is applied here to spheres in inviscid standing waves that are solid, fixed-rigid, or movable-rigid of finite density. Low frequency truncated expansions of the phase shifts result in expressions for radiation forces that have simple forms. The expansion expresses the leading finite-size correction to the common low-frequency approximation associated with Rayleigh scattering in which the radiation force is proportional to the solid sphere's volume.