Rotation of fibers and other non-spherical particles by the acoustic radiation torque

Abstract

This study is aimed at the theoretical analysis of the acoustic radiation torque and the experimental realization of a controlled rotation of non-spherical particles by ultrasound. A finite element model has been developed and validated to calculate the acoustic radiation torque on a microfiber. The influence of different parameters such as the frequency, fiber size and position in the acoustic field are evaluated. The rotational motion of a non-spherical particle and the resulting drag torque are analyzed as well. This allows for the calculation of the angular velocity of a fiber. Various rotation methods for non-spherical particles with the acoustic radiation torque have been developed, tested experimentally with a microdevice at frequencies in the MHz range and compared to each other. The first method relies on successive change of the wave propagation direction in discrete steps. Three additional rotation methods have been developed which allow for a continuous rotation and alignment at defined orientations. The methods are characterized by the modulation of one single parameter (amplitude, phase or frequency) over time.