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      Pairing Toroidal and Magnetic Dipole Resonances in Elliptic Dielectric Rod Metasurfaces for Reconfigurable Wavefront Manipulation in Reflection

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          A novel approach for reconfigurable wavefront manipulation with gradient metasurfaces based on permittivity‐modulated elliptic dielectric rods is proposed. It is shown that the required 2π phase span in the local electromagnetic response of the metasurface can be achieved by pairing the lowest magnetic dipole Mie resonance with a toroidal dipole Mie resonance, instead of using the lowest two Mie resonances corresponding to fundamental electric and magnetic dipole resonances as customarily exercised. This approach allows for the precise matching of both the resonance frequencies and quality factors. Moreover, the accurate matching is preserved if the rod permittivity is varied, allowing for constructing reconfigurable gradient metasurfaces by locally modulating the permittivity in each rod. Highly efficient tunable beam steering and beam focusing with ultrashort focal lengths are numerically demonstrated, highlighting the advantage of the low‐profile metasurfaces over bulky conventional lenses. Notably, despite using a matched pair of Mie resonances, the presence of an electric polarizability background allows to perform the wavefront shaping operations in reflection, rather than transmission. This has the advantage that any control circuitry necessary in an experimental realization can be accommodated behind the metasurface without affecting the electromagnetic response.

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          Most cited references 33

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          A Perfect Metamaterial Absorber

          We present the design for an absorbing metamaterial element with near unity absorbance. Our structure consists of two metamaterial resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a metamaterial absorber with a slightly lower predicted absorbance of 96%. This achieves a simulated full width at half maximum (FWHM) absorbance of 4% thus making this material ideal for imaging purposes. Unlike conventional absorbers, our metamaterial consists solely of metallic elements. The underlying substrate can therefore be chosen independently of the substrate's absorptive qualities and optimized for other parameters of interest. We detail the design and simulation process that led to our metamaterial, and our experiments demonstrate a peak absorbance greater than 88% at 11.5 GHz.
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            High-efficiency broadband anomalous reflection by gradient meta-surfaces.

            We combine theory and experiment to demonstrate that a carefully designed gradient meta-surface supports high-efficiency anomalous reflections for near-infrared light following the generalized Snell's law, and the reflected wave becomes a bounded surface wave as the incident angle exceeds a critical value. Compared to previously fabricated gradient meta-surfaces in infrared regime, our samples work in a shorter wavelength regime with a broad bandwidth (750-900 nm), exhibit a much higher conversion efficiency (∼80%) to the anomalous reflection mode at normal incidence, and keep light polarization unchanged after the anomalous reflection. Finite-difference-time-domain (FDTD) simulations are in excellent agreement with experiments. Our findings may lead to many interesting applications, such as antireflection coating, polarization and spectral beam splitters, high-efficiency light absorbers, and surface plasmon couplers.
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              Metamaterial Huygens' surfaces: tailoring wave fronts with reflectionless sheets.

              Huygens' principle is a well-known concept in electromagnetics that dates back to 1690. Here, it is applied to develop designer surfaces that provide extreme control of electromagnetic wave fronts across electrically thin layers. These reflectionless surfaces, referred to as metamaterial Huygens' surfaces, provide new beam shaping, steering, and focusing capabilities. The metamaterial Huygens' surfaces are realized with two-dimensional arrays of polarizable particles that provide both electric and magnetic polarization currents to generate prescribed wave fronts. A straightforward design methodology is demonstrated and applied to develop a beam-refracting surface and a Gaussian-to-Bessel beam transformer. Metamaterial Huygens' surfaces could find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, polarization controlling devices, stealth technologies, and perfect absorbers.

                Author and article information

                Adv Opt Mater
                Adv Opt Mater
                Advanced Optical Materials
                John Wiley and Sons Inc. (Hoboken )
                17 September 2018
                19 November 2018
                : 6
                : 22 ( doiID: 10.1002/adom.v6.22 )
                [ 1 ] Institute of Electronic Structure and Laser FORTH GR‐71110 Heraklion Crete Greece
                [ 2 ] Ames Laboratory—U.S. DOE and Department of Physics and Astronomy Iowa State University Ames IA 50011 USA
                [ 3 ] Department of Materials Science and Technology University of Crete GR‐71003 Heraklion Crete Greece
                [ 4 ] Department of Physics University of Crete GR‐71003 Heraklion Crete Greece
                Author notes
                © 2018 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

                This is an open access article under the terms of the License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

                Page count
                Figures: 9, Tables: 2, Pages: 9, Words: 7111
                Funded by: European Research Council
                Award ID: 320081
                Funded by: European Union's Horizon 2020
                Award ID: 736876
                Funded by: Department of Energy
                Award ID: DE‐AC02‐07CH11358
                Full Paper
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                November 19, 2018
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.5.8 mode:remove_FC converted:11.02.2019


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