Source illusion devices for flexural Lamb waves using elastic metasurfaces

TL;DR

This paper introduces elastic metasurface-based source illusion devices for flexural Lamb waves, enabling broadband manipulation of wave sources for applications in testing, sensing, and imaging.

Contribution

It presents the first experimental demonstration of metasurfaces for manipulating elastic wave sources, overcoming limitations of traditional transformation methods.

Findings

Metasurfaces can shift, transform, and split point sources for flexural waves.

The devices operate broadband and are robust to source position changes.

Experimental results agree with numerical simulations and theory.

Abstract

Metamaterials with the transformation method has greatly promoted the development in achieving invisibility and illusion for various classical waves. However, the requirement of tailor-made bulk materials and extreme constitutive parameters associated to illusion designs hampers its further progress. Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form-invariance in usual transformation methods. We demonstrate metasurfaces for shifting, transforming and splitting a point source with "space-coiling" structures. The effects are found to be broadband and robust against a change of source position, with agreement from numerical simulations and Huygens-Fresnel theory. The proposed approach provides an avenue to generically manipulate guided elastic waves in solids, and is potentially useful for applications such as non-destructive testing, enhanced sensing and imaging.