Abstract
The authors use numerical simulations and theoretical analysis to study the propagation of acoustic vortices in inhomogeneous media. The paper reveals how the vortex field and both linear and angular momenta evolve in a stratified inhomogeneous medium. The results may have applications in communication, imaging, and particle manipulations.
Highlights
We observe a series of unstable and dynamic behaviors of acoustic vortices propagating in stratified inhomogeneous media
We reveal the transport of energy by examining the time-averaged energy flux over a wave period, S = c2g [4], where the time-averaged momentum density g = Im(ψ∗∇ψ ) is calculated from the complex scalar field ψ and its gradient that gives the velocity (Im represents the imaginary part and a prefactor is suppressed in the normalization of ψ)
We found that the stratification feature leads to the distortion and complex behaviors of the vortices via the emergence of bending, distorting, focusing, and stretching of the fields, or even the reversal of the energy and momentum transports, and angular momentum
Summary
The results will be useful for applications of acoustic vortices in communication and particle manipulations in inhomogeneous media such as oceans and biomedical tissues. The integer m is the topological charge of the vortex and the field has a null at the core It is of fundamental and practical interests to study the propagation of wave vortices and transport of OAM in heterogeneous media. In inhomogeneous media is fundamental and vital to address, yet remains to be explored In this Rapid Communication, we open up the study by investigating acoustic singularities and vortices in stratified inhomogeneous media. We start by simulating the propagation of ultrasonic vortex fields in a linearly stratified fluid, where the sound speed is c = c0 − Gz, such as that considered in Refs.
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