Efficient Mode Converter and Orbital-Angular-Momentum Generator via Gradient-Index Metamaterials

Abstract

As the predominant information carrier, acoustic waves play an essential role in underwater communications, with significantly less scattering and attenuation than that of electromagnetic waves. Integrating the gradient-index metamaterials (GIMs) with circular waveguide, we propose a design to achieve a multimodal acoustic converter with multifrequency and great efficiency in a circular waveguide. Numerical simulations and analytical results demonstrate that the zeroth order of acoustic mode can be converted to the first-order mode or even higher-order modes. Moreover, optimizing the parameter of GIMs, it is further demonstrated that GIMs, attached to the rigid wall of waveguide, can be utilized as a passive orbital-angular-momentum (OAM) generator. In the future, this mode-conversion scheme with suppressed backscattering and high mode-conversion efficiency may find many applications in integrated acoustics and underwater communications.