Motion of particles driven by the primary and secondary acoustic radiation forces and formation of striae in a Kundt's tube

Abstract

The motion of a polystyrene foam sphere in a Kundt's tube is investigated and confirmed to be driven by the primary acoustic radiation force. When spheres are placed in a straight line in the direction of the tube axis, they are aligned with the tube axis at certain spaces. This phenomenon is investigated using the balance between the primary and secondary acoustic radiation forces acting on the spheres and also using the equation of motion for the spheres. When spheres are close, they exert secondary acoustic radiation forces and adhere to each other, forming lines in the direction perpendicular to the tube axis. These lines are found to be arranged at regular spaces in the direction of the tube axis by the two types of acoustic radiation forces, forming stable striae. The spacing between adjacent striae depends on factors such as sound frequency and sphere size.