Holographic Optimization Method of Acoustic Radiation Force for Continuously Manipulating a Mie Particle through a Fluid

Abstract

Acoustic holography is widely used in particle manipulation. However, previous methods focus on modulating the amplitude and phase of the target sound field. In general, the amplitude gradient and phase gradient of the sound field correspond to the gradient force and the scattering force, respectively. But the relationship between the force and the aforementioned gradient is nonlinear even for a Rayleigh particle (whose radius is much smaller than the wavelength), not to mention the Mie particle(whose radius is comparable with the wavelength). If we want to control the continuous motion of a Mie particle quantitatively, we need to design force based on the relationship among the force, acceleration, and velocity. Here we propose to design radiation force along the path of a particle directly in holography methods. Compared to the usual modulation of amplitude and phase, the method designing radiation force directly can control the acceleration and orbital limiting velocity of a two-dimensional orbit rotation of a Mie particle with radius $a=0.4\phantom{\rule{0.2em}{0ex}}\mathrm{mm}$ (approximately $2/3$ wavelength) in simulation. The experiment verified its feasibility in controlling the continuous motion of particle quantitatively. This work shows its superiority over the pure acoustic holography methods in quantitative particle manipulation.