Optical Neutrality: Invisibility without Cloaking

TL;DR

This paper demonstrates that by adjusting the metal fraction in a metamaterial, one can achieve optical neutrality, making an object invisible without traditional cloaking, through cancellation of scattering effects.

Contribution

It extends the neutral inclusion concept to Mie scatterers, showing invisibility achieved without cloaking by tuning material composition.

Findings

Increased metal fraction leads to transition from dielectric-like to metal-like scattering.

Achieved optical neutrality through cancellation of multiple scattering orders.

Demonstrated invisibility without separating the scatterer into cloak and hidden regions.

Abstract

We show that it is possible to design an invisible wavelength-sized metal-dielectric metamaterial object without evoking cloaking. Our approach is an extension of the neutral inclusion concept by Zhou and Hu [Phys.Rev.E 74, 026607 (2006)] to Mie scatterers. We demonstrate that an increase of metal fraction in the metamaterial leads to a transition from dielectric-like to metal-like scattering, which proceeds through invisibility or optical neutrality of the scatterer. Formally this is due to cancellation of multiple scattering orders, similarly to plasmonic cloaking introduced by Alu and Engheta [Phys.Rev.E 72, 016623 (2005)], but without introduction of the separation of the scatterer into cloak and hidden regions.