Extraordinary manipulations of particles by acoustic radiation forces and torques

Particle manipulations using radiation forces and torques produced by acoustic waves have been found valuable applications in biomedical and material engineering. Recent work suggests extraordinary manipulations of particles associated with direction reversals of forces and torques by some specific sound beams. When considering the three-dimensional acoustic radiation force, the momentum view enlightens into the superposition and coupling of manipulations by multiple beams and the force dependence on scattering functions [L. Zhang, JASA 144 (1), 443–447 (2018)]. It is efficient to apply the superposition to consider forces and torques on particles moved away from the equilibrium trapping position [L. Zhang, JASA 143(5), 2796–2800 (2018)]. The superposition reveals how the radiation torque associated with energy absorption can spin an object around its center of mass in a direction reversed with respect to the wave vortex’s handedness [L. Zhang, Phys. Rev. Appl. 10(3), 034039 (2018)]. These insights into extraordinary manipulations are of interest for advancing the flexibility of particle manipulations by acoustic tweezers and to the field of acoustofluidics.