Dynamical motion of an oblate shaped particle exposed to an acoustic standing wave in a microchannel

The nonlinear effects induced on a nonspherical object exposed to an acoustic standing wave offer acoustic radiation force and torque, resulting in the dynamical motion of the object. Here, we study the translational and rotational motion of an oblate shaped particle exposed to standing bulk acoustic waves in a microchannel using numerical simulations. Acoustic pressure and velocity fields are obtained from a numerical model, and a perfectly matched layer boundary condition is used to simulate the particle dynamics. A systematic parametric study is carried out to understand the effects of initial orientation, aspect ratio, size, and initial location of the particle on the translational and rotational motion, by considering the acoustic streaming effects. In this paper, we reveal that the particle undergoes rotation to minimize the acoustic radiation torque potential when the minor axis of the particle is not in line with the acoustic pressure wave direction. We find that the direction of rotation changes from anticlockwise to clockwise beyond a critical aspect ratio of the particle. The location of maximum torque and consequently particle rotation shift closer to the pressure node with increased particle size for a constant aspect ratio. Our results show that a particle positioned closer to the pressure node rapidly rotates, attributed to a sharp increase in acoustic radiation torque acting on it owing to a higher torque potential. In this paper, we shed light on the dynamical motion of an oblate shaped particle exposed to acoustic standing waves which may be relevant in understanding the dynamics of an elongated micro-organism or biological cells.