Rigorous analysis of the axial acoustic radiation force on a spherical object for single-beam acoustic tweezing applications

Acoustic tweezers are increasingly utilized for the contactless manipulation of small particles. This paper provides a theoretical model demonstrating the acoustic manipulation capabilities of single-beam acoustic transducers. Analytical formulas are derived for the acoustic radiation force on an isotropic spherical object of arbitrary size, centered on a circular piston, simply supported and clamped radiator in an inviscid fluid. Using these results, the existence of a negative axial force pulling the object closer to the radiator is revealed and explored. These findings offer further insight into the feasibility of trapping objects in the near-field of a single-beam acoustic transducer. The calculations illustrate the trapping capabilities of the different emitters as a function of radiator size, particle size, and distance from the source and highlight the impact of radiator boundary conditions. Manipulation of a cell-like fluid sphere in water and an expanded polystyrene sphere in air are studied in more detail with results that are validated through finite element analysis. The developed theoretical model allows fast evaluation of acoustic radiation forces which could aid in the development of relatively simple and inexpensive contactless manipulation solutions.