Ground-plane quasicloaking for free space

Ground-plane cloak designs are presented, which minimize scattering of electromagnetic radiation from metallic objects in the visible spectrum. It is showed that simplified ground-plane cloaks made from only a few blocks of all-dielectric isotropic materials, either embedded in a background medium or in free space, can provide considerable cloaking performance while maintaining their broadband nature. A design which operates isolated in free space that cloaks radiation originating from a specified direction is also analyzed. These schemes should be much easier to be demonstrated experimentally compared to full designs.

Figure 1

(Color online) Relative 2D permittivity maps for cloaking a triangular metallic object placed over a ground plane. The cloaks in (a)–(c) are embedded in glass $\left({\epsilon }_{ref}=2.25\right)$, while the cloaks in (d) and (e) are embedded in free space $\left({\epsilon }_{ref}=1\right)$. The colored bars indicate the relative permittivity values for each map. (a) Full nonorthogonal map consisting of $64\times 15$ cells. (b) High-resolution sampled map consisting of $80\times 20$ blocks. (c) Low-resolution sampled map consisting of $6\times 2$ blocks. (d) High-resolution sampled map consisting of $80\times 20$ blocks. (e) Low-resolution sampled map consisting of $4\times 2$ blocks.

Figure 2

(Color online) Electric-field amplitude distribution for a $2.4\text{−}\mu \text{m-wide}$, 400 THz Gaussian pulse impinging at $45°$ angle with respect to the normal to a conductive plane. The locations of the cloak and the object are outlined. [(a)–(c)] The background material is glass. [(d)–(f)] The background material is free space. [(a) and (d)] Scattering from a triangular metallic object. [(b) and (e)] Cloaks comprising of $80\times 20$ blocks cover the object. [(c) and (f)] Simplified cloaks comprising of (d) $6\times 2$ and (h) $4\times 2$ blocks, respectively, cover the object.

Figure 3

(Color online) (a) Angular distribution of the scattered field energy in free space when a 4.7-fs-long, $2.4\text{−}\mu \text{m-wide}$, 600 THz Gaussian pulse is incident. The patterns shown correspond to incidence on a flat plane, incidence on the metallic object placed on the plane, and incidence on the same object when covered with either the $80\times 20$ [Fig. 1d], the $80\times 20$ dispersive, and the $4\times 2$ [Fig. 1e] quasicloaks. (b) The corresponding amplitudes of the frequency spectra of the scattered 600 THz pulse as recorded at a $45°$ angle. [(c) and (d)] The angular (c) and frequency (d) spectra of a 1600 THz scattered pulse in the same setup.

Figure 4

(Color online) Electric-field amplitude distribution when a 12-fs-long, 400 THz Gaussian pulse impinges on a diamond-shaped metallic object in free space, parallel to its long axis. (a) Bare object. (b) Object covered with the proposed $4\times 4$ simplified all-dielectric quasicloak.