Exploring the underlying mechanism of acoustic radiation force on a sphere in a fluid-filled rigid tube

The propagation of sound waves in a fluid-filled rigid tube has potential application in acoustic particle-positioning, valuable reagent recovery, and noninvasive manipulation of targets. The interaction between sound waves and targets causes momentum transport, and the acoustic radiation force is motivated to move and rotate the targets. Generally, acoustic radiation force is related to sound scattering of the target. The relationship between acoustic radiation force and the scattering pattern will play a positive role in better explaining the phenomenon of and changed trend in acoustic radiation force acting on a particle in a tube and in predicting the acoustic control system in a tube. This paper studies the interactions between a plane sound wave and a sphere in a fluid-filled rigid tube and tries to explore the relationship between acoustic radiation force and the dimensionless complex scattering pattern. The spherical particle with different materials is studied for Rayleigh scattering and Mie-like scattering. Simulation results show that there is a certain relationship between the acoustic radiation force and the scattering pattern for a spherical particle. At the resonance frequency, which corresponds to the natural frequencies of the vibration of fluid filled in the cavity with the rigid wall, both acoustic radiation force and the backscattering form function show identical resonance characteristics. At Rayleigh scattering and Mie-like scattering regimes, when the backscattering is greater than the forward scattering, acoustic radiation forces show an increasing trend compared with the dimensional frequency. However, with the increase in dimensionless frequency, the acoustic radiation force does not respond to the forward scattering except the resonance positions in the transition region from Mie-like scattering regimes to the geometric scattering regimes. When a negative force occurs near the resonance position, the scattering in the back hemisphere is weaker than that of the front hemisphere. This study will help predict the various behaviors of radiation force using the measured backscattering echo and the forward scattering wave, and it can provide reference to the control of the acoustic manipulation system effectively and precisely.