83 research outputs found
Design, Concepts and Applications of Electromagnetic Metasurfaces
The paper overviews our recent work on the synthesis of metasurfaces and
related concepts and applications. The synthesis is based on generalized sheet
transition conditions (GSTCs) with a bianisotropic surface susceptibility
tensor model of the metasurface structure. We first place metasurfaces in a
proper historical context and describe the GSTC technique with some fundamental
susceptibility tensor considerations. Upon this basis, we next provide an
in-depth development of our susceptibility-GSTC synthesis technique. Finally,
we present five recent metasurface concepts and applications, which cover the
topics of birefringent transformations, bianisotropic refraction, light
emission enhancement, remote spatial processing and nonlinear second-harmonic
generation
Simulation of Metasurfaces in Finite Difference Techniques
We introduce a rigorous and simple method for analyzing metasurfaces, modeled
as zero-thickness electromagnetic sheets, in Finite Difference (FD) techniques.
The method consists in describing the spatial discontinuity induced by the
metasurface as a virtual structure, located between nodal rows of the Yee grid,
using a finite difference version of Generalized Sheet Transition Conditions
(GSTCs). In contrast to previously reported approaches, the proposed method can
handle sheets exhibiting both electric and magnetic discontinuities, and
represents therefore a fundamental contribution in computational
electromagnetics. It is presented here in the framework of the FD Frequency
Domain (FDFD) method but also applies to the FD Time Domain (FDTD) scheme. The
theory is supported by five illustrative examples
Surface-Wave Dispersion Retrieval Method and Synthesis Technique for Bianisotropic Metasurfaces
We propose a surface-wave dispersion retrieval method and synthesis technique
that applies to bianisotropic metasurfaces that are embedded in symmetric or
asymmetric environments. Specifically, we use general zero-thickness sheet
transition conditions to relate the propagation constants of surface-wave modes
to the bianisotropic susceptibility components of the metasurface, which can
themselves be directly related to its scattering parameters. It is then
possible to either obtain the metasurface dispersion diagram from its known
susceptibilities or, alternatively, compute the susceptibilities required to
achieve a desired surface-wave propagation. The validity of the method is
demonstrated by comparing its results to those obtained with exact dispersion
relations of well known structures such as the propagation of surface plasmons
on thin metallic films. In particular, this work reveals that it is possible to
achieve surface-wave propagation only on one side of the metasurface either by
superposition of symmetric and asymmetric modes in the case of anisotropic
metasurfaces or by completely forbidding the existence of the surface wave on
one side of the structure using bianisotropic metasurfaces
Efficient Analysis of Metasurfaces in Terms of Spectral-Domain GSTC Integral Equations
We present a spectral-domain (SD) technique for the efficient analysis of
metasurfaces. The metasurface is modeled by generalized sheet transition
conditions (GSTCs) as a zero-thickness sheet creating a discontinuity in the
electromagnetic field. The SD expression of these GSTCs for a specified
incident field leads to a system of four surface integral equations for the
reflected and transmitted fields, which are solved using the method of moments
in the spectral domain. Compared to the finite-difference and finite-element
techniques that require meshing the entire computational domain, the proposed
technique reduces the problem to the surface of the metasurface, hence
eliminating one dimension and providing substantial benefits in terms of memory
and speed. A monochromatic generalized-refractive metasurface and a
polychromatic focusing metasurface are presented as illustrative examples
Study of the Angular Spectrum of a Bianisotropic Refractive Metasurface at a Dielectric Interface
We present an initial study of the angular spectrum of a bianisotropic
refractive metasurface at an interface between two dielectric media. In this
study, we report on the existence of three distinct angular regions: a)~a
rotated transmission cone, b)~a modified total internal reflection region, and
c)~a new total retro-reflection region
General Metasurface Synthesis Based on Susceptibility Tensors
A general method, based on susceptibility tensors, is proposed for the
synthesis of metasurfaces transforming arbitrary incident waves into arbitrary
reflected and transmitted waves. The proposed method exhibits two advantages:
1)it is inherently vectorial, and therefore better suited for full vectorial
(beyond paraxial) electromagnetic problems, 2) it provides closed-form
solutions, and is therefore extremely fast. Incidentally, the method reveals
that a metasurface is fundamentally capable to transform up to four independent
wave triplets (incident, reflected and refracted waves). In addition, the paper
provides the closed-form expressions relating the synthesized susceptibilities
and the scattering parameters simulated within periodic boundary conditions,
which allows one to design the scattering particles realizing the desired
susceptibilities. The versatility of the method is illustrated by examples of
metasurfaces achieving the following transformations: generalized refraction,
reciprocal and non-reciprocal polarization rotation, Bessel vortex beam
generation, and orbital angular momentum multiplexing
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