Acoustic Radiation Force on an Eccentric Layered Fluid Sphere Exerted by a Focused Gaussian Beam

A comprehensive analytical formalism is presented for the acoustic radiation force exerted on an eccentric layered fluid sphere immersed in an ideal fluid and subjected to a focused Gaussian beam field. A closed-form expression for the acoustic radiation force is derived by applying the partial-wave series expansion method and the translational addition theorem in spherical coordinates. Numerical computations are performed on the non-dimensional axial acoustic radiation force function, which represents the acoustic radiation force per unit energy density and unit cross-sectional surface. Particular emphases are put on evaluating the effects of the dimensionless size parameter, the eccentric distance, the beam waist and the distance from the beam center to the sphere. The simulated results show that the relative size of the inner sphere and the eccentric distance mainly influence the radiation force at high frequencies. A larger beam waist leads to the enlargement of the cross section and then the enhancement of the acoustic radiation force. The effects on the radiation force of varying the outer and inner materials of the sphere are also considered. The results in this study can improve our understanding of the acoustic radiation force behaviors for eccentric spherical particles.