Analytical, numerical and experimental investigation of Luneburg lens system for directional cloaking

TL;DR

This paper presents an analytical, numerical, and experimental study of a Luneburg lens system for directional cloaking, demonstrating its ability to hide objects by guiding light around a designated dark zone.

Contribution

It introduces a novel cloaking design using an array of Luneburg lenses, discretized into a photonic crystal structure, and verifies its effectiveness through experiments at microwave frequencies.

Findings

Cloaking achieved by light bypassing the object within the dark zone.

Numerical simulations closely match experimental results.

Effective cloaking demonstrated at around 8 GHz frequency.

Abstract

In this study, the design of a directional cloaking based on the Luneburg lens system is proposed and its operating principle is experimentally verified. The cloaking concept is analytically investigated via geometrical optics and numerically realized with the help of the finite-difference time-domain method. In order to benefit from its unique focusing and/or collimating characteristics of light, the Luneburg lens is used. We show that by the proper combination of Luneburg lenses in an array form, incident light bypasses the region between junctions of the lenses, i.e., the "dark zone." Hence, direct interaction of an object with propagating light is prevented if one places the object to be cloaked inside that dark zone. This effect is used for hiding an object which is made of a perfectly electric conductor material. In order to design an implementable cloaking device, the Luneburg lens is discretized into a photonic crystal structure having gradually varying air cylindrical holes in a dielectric material by using Maxwell Garnett effective medium approximations. Experimental verifications of the designed cloaking structure are performed at microwave frequencies of around 8 GHz. The proposed structure is fabricated by three-dimensional printing of dielectric polylactide material and a brass metallic alloy is utilized in place of the perfectly electric conductor material in microwave experiments. Good agreement between numerical and experimental results is found.