320 research outputs found
Gap deformation and classical wave localization in disordered two-dimensional photonic band gap materials
By using two ab initio numerical methods we study the effects that disorder
has on the spectral gaps and on wave localization in two-dimensional photonic
band gap materials. We find that there are basically two different responses
depending on the lattice realization (solid dielectric cylinders in air or vise
versa), the wave polarization, and the particular form under which disorder is
introduced. Two different pictures for the photonic states are employed, the
``nearly free'' photon and the ``strongly localized'' photon. These originate
from the two different mechanisms responsible for the formation of the spectral
gaps, ie. multiple scattering and single scatterer resonances, and they
qualitatively explain our results.Comment: Accepted for publication in Phys. Rev.
Robustness of One-Dimensional Photonic Bandgaps Under Random Variations of Geometrical Parameters
The supercell method is used to study the variation of the photonic bandgaps
in one-dimensional photonic crystals under random perturbations to thicknesses
of the layers. The results of both plane wave and analytical band structure and
density of states calculations are presented along with the transmission
cofficient as the level of randomness and the supercell size is increased. It
is found that higher bandgaps disappear first as the randomness is gradually
increased. The lowest bandgap is found to persist up to a randomness level of
55 percent.Comment: Submitted to Physical Review B on April 8 200
Absorption losses in periodic arrays of thin metallic wires
We analyze the transmission and reflection of the electromagnetic wave
calculated from transfer matrix simulations of periodic arrangements of thin
metallic wires. The effective permittivity and the absorption is determined.
Their dependence on the wire thickness and the conductance of the metallic
wires is studied. The cutoff frequency or effective plasma frequency is
obtained and is compared with analytical predictions. It is shown that the
periodic arrangement of wires exhibits a frequency region in which the real
part of the permittivity is negative while its imaginary part is very small.
This behavior is seen for wires with thickness as small as 17 m with a
lattice constant of 3.33 mm
Nonlocal electrodynamics of two-dimensional wire mesh photonic crystals
We calculate analytically the spectra of plasma waves and electromagnetic
waves (EMW) in metallic photonic crystal consisting of the parallel thin
infinite metallic cylinders embedded in the dielectric media. The axes of
metallic cylinders form a regular square lattice in a plane perpendicular to
them. The metal inside the cylinders is assumed to be in the high frequency
regime , where is the relaxation time. The proposed
analytical theory is based upon small parameters , where is the
volume fraction of the metal, and , where is the wave vector and
is the radius of the cylinder. It is shown that there are five different
branches of the EMW that cover all frequency range under consideration except
one very small omnidirectional gap in the vicinity of the frequency of the
surface plasmon. However, at some directions of propagation and polarizations
the gap may be much larger. The reflection and refraction of the EMW is also
considered. The general theory of refraction is proposed which is complicated
by the spatial dispersion of the dielectric constant, and one particular
geometry of the incident EMW is considered.Comment: 14 pages, 8 figure
Journal of Nanoscience with Advanced Technology Hydrogen storage in Lithium, Sodium, and Potassium nanoparticles
Abstract Using Density Functional Theory (DFT), the desorption energies of Hydrogen in Lithium, Sodium, and Potassium nanoparticles is calculated. The type of nanoparticles studied were M n H xn with M=Li, Na, K and n varying from 2 up to 30. For each nanoparticle, several different geometries were studied in order to find the one with the lowest energy. The results were compared with similar calculated results for Beryllium and Magnesium nanoparticles. Mixed Li n-x Na x H n nanoparticles were also studied
Viscoelastic response of sonic band-gap materials
A brief report is presented on the effect of viscoelastic losses in a high
density contrast sonic band-gap material of close-packed rubber spheres in air.
The scattering properties of such a material are computed with an on-shell
multiple scattering method, properties which are compared with the lossless
case. The existence of an appreciable omnidirectional gap in the transmission
spectrum, when losses are present, is also reported.Comment: 5 pages, 4 figures, submitted to PR
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