Cylindrical Invisibility Cloak with Simplified Material Parameters is Inherently Visible

TL;DR

This paper demonstrates that simplified cylindrical invisibility cloaks are inherently visible because they allow the zeroth-order wave to pass through, making the cloak detectable, despite some properties inherited from ideal cloaks.

Contribution

It reveals the fundamental limitation of simplified cloaks, showing they cannot achieve perfect invisibility due to inherent visibility of the zeroth-order wave.

Findings

Zeroth-order wave passes through simplified cloak, causing visibility.

High-order waves experience finite scattering, partially inheriting ideal cloak properties.

Simplified material parameters inherently limit the cloak's invisibility.

Abstract

It was proposed that perfect invisibility cloaks can be constructed for hiding objects from electromagnetic illumination (Pendry et al., Science 312, p. 1780). The cylindrical cloaks experimentally demonstrated (Schurig et al., Science 314, p. 997) and proposed (Cai et al., Nat. Photon. 1, p. 224) have however simplified material parameters in order to facilitate easier realization as well as to avoid infinities in optical constants. Here we show that the cylindrical cloaks with simplified material parameters inherently allow the zeroth-order cylindrical wave to pass through the cloak as if the cloak is made of a homogeneous isotropic medium, and thus visible. To all high-order cylindrical waves, our numerical simulation suggests that the simplified cloak inherits some properties of the ideal cloak, but finite scatterings exist.