Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials

TLDR

Slow wave propagation in materials is a key research focus, yet conventional dispersive designs with local resonators inevitably distort waveforms. The study aims to demonstrate that helical‑structured acoustic metamaterials enable dispersion‑free sound deceleration, facilitating enhanced wave–matter interaction, phase engineering, and spatial compression. By employing tunable helicity, the helical‑structured metamaterials achieve a non‑dispersive high effective refractive index and wavefront revolution that reduce group velocity. Numerical and experimental results show that the designed helical‑structured metamaterials convert a normally incident plane wave into a self‑accelerating beam along a parabolic trajectory, highlighting their potential to advance slow‑wave physics applications.

Abstract

Abstract The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave–matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics.