Total-internal-reflection elastic metasurfaces: design and application to structural vibration isolation

TL;DR

This paper introduces Total Internal Reflection metasurfaces (TIR-MS) for elastic wave control, enabling complete wave reflection and vibration isolation in structures through engineered phase gradients and resonant elements.

Contribution

The study develops a novel TIR-MS design that achieves wave reflection beyond critical angles, extending its application from flat waveguides to circular plates for effective vibration isolation.

Findings

Numerical and experimental validation of wave reflection at target frequency

Effective vibration isolation for waves from any incident angle

Demonstration of TIR-MS in various structural geometries

Abstract

This letter presents the concept of Total Internal Reflection metasurface (TIR-MS) which supports the realization of structure-embedded subwavelength acoustic shields for elastic waves propagating in thin waveguides. The proposed metasurface design exploits extreme phase gradients, implemented via locally resonant elements, in order to achieve operating conditions that are largely beyond the critical angle. Such artificial discontinuity is capable of producing complete reflection of the incoming waves regardless of the specific angle of incidence. From a practical perspective, the TIR-MS behaves as a sound hard barrier that is impenetrable to long-wavelength modes at a selected frequency. The TIR metasurface concept is first conceived for a flat interface embedded in a rectangular waveguide and designed to block longitudinal S0-type guided modes. Then, it is extended to circular plates in order to show how enclosed areas can be effectively shielded by incoming waves. Given the same underlying physics, an equivalent dynamic behavior was also numerically and experimentally illustrated for flexural A0-type guided modes. This study shows numerical and experimental evidence that, when the metasurface is excited at the target frequency, significant vibration isolation can be achieved in presence of waves having any arbitrary angle of incidence. These results open interesting paths to achieve vibration isolation and energy filtering in certain prototypical structures of interest for practical engineering applications.