Browsing by Author "Urzhumov, YA"

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    Cross-section comparisons of cloaks designed by transformation optical and optical conformal mapping approaches
    (Journal of Optics, 2011-02-01) Urzhumov, YA; Kundtz, NB; Smith, DR; Pendry, JB
    We review several approaches to optical invisibility designed using transformation optics (TO) and optical conformal mapping (CM) techniques. TO is a general framework for solving inverse scattering problems based on mimicking spatial coordinate transformations with distributions of material properties. There are two essential steps in the design of TO media: first, a coordinate transformation that achieves some desired functionality, resulting in a continuous spatial distribution of constitutive parameters that are generally anisotropic; and, second, the reduction of the derived continuous constitutive parameters to a metamaterial that serves as a stepwise approximation. We focus here on the first step, discussing the merits of various TO strategies proposed for the long-sought 'invisibility cloak'-a structure that renders opaque objects invisible. We also evaluate the cloaking capabilities of structures designed by the related CM approach, which makes use of conformal mapping to achieve index-only material distributions. The performance of the various cloaks is evaluated and compared using a universal measure-the total (all-angle) scattering cross section. © 2011 IOP Publishing Ltd.
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    Going beyond Axisymmetry: 2.5D Vector Electromagnetics
    (2012-10) Urzhumov, YA; Landy, N; Ciraci, C; Smith, DR
    Linear wave propagation through inhomogeneous structures of size R≫λ (Fig.1) is a computationally challenging problem, in particular when using finite element methods, due to the steep increase of the number of degrees of freedom as a function of R/λ. Fortunately, when the geometry of the problem possesses symmetries, one may choose an appropriate basis in which the stiffness matrix of the discretized problem is block-diagonal. A particular scenario is the case of a cylindrically-symmetric geometry, where an appropriate basis is the set of cylindrical waves with all possible azimuthal numbers (m). Each of the excited cylindrical harmonics propagate through the structure independently of all other harmonics, and therefore the fields associated with that harmonic can be found by solving an essentially two-dimensional PDE problem in the ρ-z (half)-plane. The cylindrical waves have a prescribed dependence on the azimuthal angle variable (φ), hence the name – 2.5D electromagnetics. This novel approach is applied to the problem of cloaking and wave scattering off a spherical nanoparticle on metallic and/or dielectric substrates.
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    Nanophotonics: Optical time reversal with graphene
    (2013-07) Urzhumov, YA; Ciraci, C; Smith, DR
    Would you ever guess that a microscopic flake of graphite could reverse the diffraction of light? An experiment that demonstrates just such an effect highlights the exciting optical applications of graphene — an atomic layer of carbon with a two-dimensional honeycomb lattice.
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    Structurally Rigid Elastic Composites for Acoustic Imaging Countermeasures
    (2013-06-07) Urzhumov, YA; Starr, AF; Smith, DR
    We explore the possibilities coming from transformation acoustics and beyond for creating rigid elastic composite shells capable of suppressing the total scattering cross-section of acoustically large objects. The reported design methodology is based on generalized shape and topology optimization, and the outcomes are suitable for rapid prototyping techniques.
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    Towards macroscopic optical invisibility devices: geometrical optics of complex materials
    (2012-01-18) Urzhumov, YA; Smith, DR
    Recently, a path towards macroscopic, transparent optical cloaking devices that may conceal objects spanning millions of wavelengths has been proposed [1]. Such devices are designed using transformation optics (TO) [2,3]. In this paper, we offer further analysis and improvements to the concept using the method of geometrical optics extended to complex photonic media with an arbitrary dispersion relation. A technique for solving the highly nonlinear partial differential equation of the eikonal using the finite element method is presented. Aberra-tions caused by the non-quadratic part of the dispersion relation are demonstrated quantitatively in a numerical experiment. An analytical argument based on the scalability of the eikonal phase is presented, which points to-wards a solution that removes this type of aberration in each order of the k-perturbation theory, thus restoring the perfect cloaking solution.