Nonlocal metasurface for flexural wave in thin elastic plate

Abstract

Recent advancements in metasurfaces indicate that achieving high efficiency requires nonlocal designs where the coupling between constituent units is fully considered. However, most metasurfaces for elastic waves are still designed as local structures based on the generalized Snell's law (GSL), which often results in low efficiency. In this paper, we extend a previously proposed method for acoustic metasurfaces to design nonlocal structures for elastic waves. Using this method, we design anomalous reflectors and planar focusers with large numerical apertures for flexural waves in thin elastic plates. Through three-dimensional finite element simulations, we demonstrate that the proposed anomalous reflectors can achieve near-unity efficiency, even for structures with a deflection angle as large as 85°. For the planar focuser, the focusing efficiency of our nonlocal designs is shown to be significantly higher than that of their GSL-based counterparts, particularly for structures with numerical apertures approaching unity. This work not only introduces an efficient design method for nonlocal metasurfaces for flexural waves in thin elastic plates but also provides two highly efficient nonlocal structures with promising applications in areas such as sensing, energy harvesting, and more.