Three-dimensional acoustical radiation forces in the view of momentum conservation

Analysis of acoustic radiation forces is essential for tailoring parameters for desired manipulations or for interpreting special force conditions. Previous theoretical derivation for acoustic radiation forces was from integration of stress tensor of the total fields. Given that the force is a second-order effect, interactions between the incident and scattered fields or between different beams contribute to the forces and complicate the analysis. Here the three-dimensional forces exerted by an arbitrary field is presented in the framework of momentum conservation where force superposition is possible for flexible analysis. The force is related to momentum transfers by ingoing and outgoing spherical waves and to momentum transfers associated with extinction and scattering. Superposition of forces based on orthogonality of momentum and insight into force dependence on beam and scattering parameters for special manipulations are addressed.