Acoustic Modes with Spin Angular Momentum in Cylindrical Resonator

This article examines acoustic vortex modes within an acoustofluidic cavity filled with a viscous fluid. By employing a cylindrical geometry and applying phased time-harmonic excitation at the cavity base, these modes are induced. We derive dynamic pressure equations and boundary conditions, considering the no-slip condition on internal surfaces. The resulting pressure amplitude solution is expressed using resonance functions that incorporate fluid damping and viscous boundary layer effects. Additionally, pressure distribution is described using eigenfunctions of the Helmholtz equation in cylindrical coordinates. We analyze single-mode configurations and explore associated wave phenomena, including energy density, acoustic radiation force, and spin angular momentum. Our findings, validated against finite element simulations with water and olive oil, provide insights into confined acoustic standing waves within acoustofluidic systems, considering viscous effects and spin angular momentum.