Broadband focusing and collimation of water waves by zero refractive index

Abstract

It is always a challenge to realize extreme and unusual values of refractive index for a broad range of frequencies. We show that when water is covered by a thick, rigid and unmovable plate, it behaves like a medium with zero refractive index for water waves at any frequency. Hence, by covering water with a plate of a concave or rectangular shape, water waves can be focused or collimated in a broad range of frequencies. Experiments were conducted to demonstrate these effects and results are in excellent agreement with numerical simulations.

Scattering of gravity waves by a periodically structured ridge of finite extent

“…the introductory discussion in Porter (2017). Such metamaterial devices have been proposed to produce a lensing effect (Hu & Chan 2005;Zhang, Chan & Hu 2014;Bobinski et al 2015), to control the ocean wave energy flow (Chen et al 2009;Berraquero et al 2013;Dupont et al 2015) or to produce a protected free wave region using cloaking strategies (Farhat et al 2008;Newman 2014;Porter & Newman 2014;Xu et al 2015;Zareei & Alam 2015;Dupont et al 2016;Porter 2017). For most cases, the idea is to exploit an effective anisotropy resulting from a bathymetry varying at the subwavelength scale.…”