Experimental demonstration of a free space cylindrical cloak without superluminal propagation

TL;DR

This paper reports the experimental realization of a broadband cylindrical invisibility cloak in free space using anisotropic metamaterials, combining advantages of existing strategies and avoiding superluminal wave propagation.

Contribution

It introduces a novel cloaking approach based on scattering cancellation with anisotropic metamaterials, achieving broadband operation without superluminal propagation.

Findings

Successful experimental demonstration of a broadband free-space cylindrical cloak

Inherits non-superluminal wave propagation from non-Euclidean cloaks

Provides a pathway for practical large-scale cloaking devices

Abstract

We experimentally demonstrated an alternative approach of invisibility cloaking that can combine technical advantages of all current major cloaking strategies in a unified manner and thus can solve bottlenecks of individual strategies. A broadband cylindrical invisibility cloak in free space is designed based on scattering cancellation (the approach of previous plasmonic cloaking), and implemented with anisotropic metamaterials (a fundamental property of singular-transformation cloaks). Particularly, non-superluminal propagation of electromagnetic waves, a superior advantage of non-Euclidian-transformation cloaks constructed with complex branch cuts, is inherited in this design, and thus is the reason of its relatively broad bandwidth. This demonstration provides the possibility for future practical implementation of cloaking devices at large scales in free space.