715 research outputs found
Calculation of material properties and ray tracing in transformation media
Complex and interesting electromagnetic behavior can be found in spaces with
non-flat topology. When considering the properties of an electromagnetic medium
under an arbitrary coordinate transformation an alternative interpretation
presents itself. The transformed material property tensors may be interpreted
as a different set of material properties in a flat, Cartesian space. We
describe the calculation of these material properties for coordinate
transformations that describe spaces with spherical or cylindrical holes in
them. The resulting material properties can then implement invisibility cloaks
in flat space. We also describe a method for performing geometric ray tracing
in these materials which are both inhomogeneous and anisotropic in their
electric permittivity and magnetic permeability
Design of Electromagnetic Cloaks and Concentrators Using Form-Invariant Coordinate Transformations of Maxwell's Equations
The technique of applying form-invariant, spatial coordinate transformations
of Maxwell's equations can facilitate the design of structures with unique
electromagnetic or optical functionality. Here, we illustrate the
transformation-optical approach in the designs of a square electromagnetic
cloak and an omni-directional electromagnetic field concentrator. The
transformation equations are described and the functionality of the devices is
numerically confirmed by two-dimensional finite element simulations. The two
devices presented demonstrate that the transformation optic approach leads to
the specification of complex, anisotropic and inhomogeneous materials with well
directed and distinct electromagnetic behavior.Comment: submitted to "Photonics and Nanostructures", Special Issue "PECS
VII", Elsevie
Full-wave simulations of electromagnetic cloaking structures
Based on a coordinate transformation approach, Pendry {\it et al.} have
reported electromagnetically anisotropic and inhomogeneous shells that, in
theory, completely shield an interior structure of arbitrary size from
electromagnetic fields without perturbing the external fields. We report
full-wave simulations of the cylindrical version of this cloaking structure
using ideal and nonideal (but physically realizable) electromagnetic parameters
in an effort to understand the challenges of realizing such a structure in
practice. The simulations indicate that the performance of the electromagnetic
cloaking structure is not especially sensitive to modest permittivity and
permeability variations. This is in contrast to other applications of
engineered electromagnetic materials, such as subwavelength focusing using
negative refractive index materials. The cloaking performance degrades smoothly
with increasing loss, and effective low-reflection shielding can be achieved
with a cylindrical shell composed of an eight (homogeneous) layer approximation
of the ideal continuous medium
Quantum properties of two-dimensional electron gas in the inversion layer of Hg1âxCdxTe bicyrstals
The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p-type Hg1âxCdxTe bicrystals are investigated. The results clearly demonstrate the existence of a two-dimensional degenerate n-type inversion layer in the vicinity of the grain boundary. Hydrostatic pressure up to 103 MPa is used to characterize the properties of the two-dimensional electron gas in the inversion layer. At atmospheric pressure three series of quantum oscillations are revealled, indicating that tthree electric subbands are occupied. From quantum oscilations of the magnetoresistivity the characteristics parameters of the electric subbands (subband populations nsi, subband energies EFâEi, effective electron masses m*ci) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied A simple theoretical model based on the triangular-well approximation and taking into account the pressure dependence of the energy band structure of Hg1âxCdxTe is use to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters
A gradient index metamaterial
Metamaterials--artificially structured materials with tailored
electromagnetic response--can be designed to have properties difficult to
achieve with existing materials. Here we present a structured metamaterial,
based on conducting split ring resonators (SRRs), which has an effective
index-of-refraction with a constant spatial gradient. We experimentally confirm
the gradient by measuring the deflection of a microwave beam by a planar slab
of the composite metamaterial over a broad range of frequencies. The gradient
index metamaterial represents an alternative approach to the development of
gradient index lenses and similar optics that may be advantageous, especially
at higher frequencies. In particular, the gradient index material we propose
may be suited for terahertz applications, where the magnetic resonant response
of SRRs has recently been demonstrated
Some considerations on the transmissivity of thin metal films
Copyright © 2008 Optical Society of America. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-22-17258 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.As interest in plasmonics grows the optical properties of thin metal films becomes increasingly significant. Here we explore the
transmissivity of thin metal films at normal incidence, from the ultraviolet to microwaves, and show how, contrary to simplistic treatments, the microwave transmissivity may be much less than the optical transmissivity for films which are well below the skin depth in thickness. This arises because the film is acting as a zero order Fabry-Perot with very high reflectivity at each interface. The skin depth then becomes irrelevant for thin
metal films at microwave frequencies. We also note in passing that the expected exponential dependence on thickness at higher thicknesses has an asymptotic limit at zero thickness which may be as high as four times the input intensity
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