We propose generalized magnetic mirrors that can be achieved by excitations of sole electric resonances. Conventional approaches to obtain magnetic mirrors rely heavily on exciting the fundamental magnetic dipoles, whereas here we reveal that, besides magnetic resonances, electric resonances of higher orders can be also employed to obtain highly efficient magnetic mirrors. Based on the electromagnetic duality, it is also shown that electric mirrors can be achieved by exciting magnetic resonances. We provide direct demonstrations of the generalized mirrors proposed in a simple system of a one-dimensional periodic array of all-dielectric wires, which may shed new light on many advanced fields of photonics related to resonant multipolar excitations and interferences.

Generalized magnetic mirrors

We study optical wave manipulations through high-index dielectric metalattices in both diffractionless metasurface and diffractive metagrating regimes. It is shown that the collective lattice couplings can be employed to tune the excitation efficiencies of all electric and magnetic multipoles of various orders supported by each particle within the metalattice. The interferences of those adjusted multipoles lead to highly asymmetric angular scattering patterns that are totally different from those of isolated particles, which subsequently enables flexible beam manipulations, including perfect reflection, perfect transmission, and efficient large-angle beam steering. The revealed functioning mechanism of manipulated interplays between lattice couplings and multipolar interferences can shed new light on both photonic branches of metasurfaces and metagratings, which can potentially inspire many advanced applications related to optical beam controls.

Beam Steering with Dielectric Metalattices

In this paper the electromagnetic wave scattering from multilayered cylindrical structures is studied for a normally incident plane wave with linear (TE or TM), circular and elliptical polarizations. The cylindrical layers may be composed of any combination of dispersive common materials and metamaterials. The addition theorems for the cylindrical waves are used for the EM wave analysis. The objective of this study is to decrease or increase the Radar Cross Section (RCS) in an ultra wide band width. The optimization is based on the Method of Least Squares (MLS), employing a novel combination of the Genetic Algorithm (GA) and Conjugate Gradient (CG), where the global search for the minimization point is performed by GA and the local search is done by CG, which greatly speeds up the search algorithm. The behaviors of various combinations of common materials and metamaterials for reduction of RCS are studied. Furthermore, the procedures for selection of correct signs for metamaterial parameters, namely e, µ, k and η are presented.

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Combination of mls, ga & cg for the reduction of rcs of multilayered cylindrical structures composed of dispersive metamaterials

—This paper proposes the pseudo-periodic Fourier transform to analyze the electromagnetic scattering from periodic structures with non-plane wave incidence The pseudo-periodic Fourier transform converts arbitrary field components into pseudo-periodic functions and the conventional grating theories based on the Floquet theorem become applicable The inverse transform is given by integrating with respect to the transform parameter over a finite interval and the near field analysis requires numerical integration Some application examples are numerically examined and the results show good convergence

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Two-Dimensional Electromagnetic Scattering of Non-Plane Incident Waves by Periodic Structures

The addition theorems are applied to analyze the normal incidence of plane waves onto infinitely long conducting or dielectric circular cylinders with multilayer coatings made of common and uncommon materials (er ,µ r ,σ ) with the objective of minimization and maximization of radar cross-section (RCS). TE, TM and circular polarizations of the incident wave are considered. Optimization of RCS by the method of least squares leads to the determination of layer thicknesses and the material complex permittivities and permeabilities. A sensitivity analysis of RCS with respect to the geometrical and material parameters of the multilayer coated conducting cylinder is also performed. It is observed that broadband reduction of RCS is mostly achievable by a combination of conventional materials (er ,µ r > 1), and unconventional materials (0 0). It is seen that RCS reduction is due to the diversion and dissipation of radar signals. The results agree very well with the experimental and theoretical data available in the literature.

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Ultra wide band rcs optimization of multilayerd cylindrical structures for arbitrarily polarized incident plane waves

The two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders is studied. The incident Gaussian beam is expressed as a superposition of plane waves of different amplitudes and different incident angles, using the plane-wave spectrum technique based on Fourier optics. For each plane wave, the scattered field is calculated with the T-matrix of an isolated circular cylinder and its lattice sums characterizing a periodic arrangement of the circular cylinders. The circular cylinders may be perfect conductors, dielectric or gyrotropic cylinders, as long as their T-matrices are known.

Chang-Hong Liang

Papers

Two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders