162 research outputs found
Opaque perfect lenses
The response of the ``perfect lens'', consisting of a slab of lossless
material of thickness with at one frequency is
investigated. It is shown that as time progresses the lens becomes increasingly
opaque to any physical TM line dipole source located a distance from
the lens and which has been turned on at time . Here a physical source is
defined as one which supplies a bounded amount of energy per unit time. In fact
the lens cloaks the source so that it is not visible from behind the lens
either. For sources which are turned on exponentially slowly there is an exact
correspondence between the response of the perfect lens in the long time
constant limit and the response of lossy lenses in the low loss limit. Contrary
to the usual picture where the field intensity has a minimum at the front
interface we find that the field diverges to infinity there in the long time
constant limit.Comment: The 7th International Conference on the Electrical transport and
Optical Properties of Inhomogenous Media (ETOPIM7
A metamaterial frequency-selective super-absorber that has absorbing cross section significantly bigger than the geometric cross section
Using the idea of transformation optics, we propose a metamaterial device
that serves as a frequency-selective super-absorber, which consists of an
absorbing core material coated with a shell of isotropic double negative
metamaterial. For a fixed volume, the absorption cross section of the
super-absorber can be made arbitrarily large at one frequency. The double
negative shell serves to amplify the evanescent tail of the high order incident
cylindrical waves, which induces strong scattering and absorption. Our
conclusion is supported by both analytical Mie theory and numerical finite
element simulation. Interesting applications of such a device are discussed.Comment: 16 pages, 5 figure
Superscatterer: Enhancement of scattering with complementary media
Based on the concept of complementary media, we propose a novel design which
can enhance the electromagnetic wave scattering cross section of an object so
that it looks like a scatterer bigger than the scale of the device. Such a
``superscatterer'' is realized by coating a negative refractive material shell
on a perfect electrical conductor cylinder. The scattering field is
analytically obtained by Mie scattering theory, and confirmed by full-wave
simulations numerically. Such a device can be regarded as a cylindrical concave
mirror for all angles.Comment: 9 pages, 4 figure
Numerical Analysis of Three-dimensional Acoustic Cloaks and Carpets
We start by a review of the chronology of mathematical results on the
Dirichlet-to-Neumann map which paved the way towards the physics of
transformational acoustics. We then rederive the expression for the
(anisotropic) density and bulk modulus appearing in the pressure wave equation
written in the transformed coordinates. A spherical acoustic cloak consisting
of an alternation of homogeneous isotropic concentric layers is further
proposed based on the effective medium theory. This cloak is characterised by a
low reflection and good efficiency over a large bandwidth for both near and far
fields, which approximates the ideal cloak with a inhomogeneous and anisotropic
distribution of material parameters. The latter suffers from singular material
parameters on its inner surface. This singularity depends upon the sharpness of
corners, if the cloak has an irregular boundary, e.g. a polyhedron cloak
becomes more and more singular when the number of vertices increases if it is
star shaped. We thus analyse the acoustic response of a non-singular spherical
cloak designed by blowing up a small ball instead of a point, as proposed in
[Kohn, Shen, Vogelius, Weinstein, Inverse Problems 24, 015016, 2008]. The
multilayered approximation of this cloak requires less extreme densities
(especially for the lowest bound). Finally, we investigate another type of
non-singular cloaks, known as invisibility carpets [Li and Pendry, Phys. Rev.
Lett. 101, 203901, 2008], which mimic the reflection by a flat ground.Comment: Latex, 21 pages, 7 Figures, last version submitted to Wave Motion.
OCIS Codes: (000.3860) Mathematical methods in physics; (260.2110)
Electromagnetic theory; (160.3918) Metamaterials; (160.1190) Anisotropic
optical materials; (350.7420) Waves; (230.1040) Acousto-optical devices;
(160.1050) Acousto-optical materials; (290.5839) Scattering,invisibility;
(230.3205) Invisibility cloak
Conductance of photons and Anderson localization of light
Conductance properties of photons in disordered two-dimensional photonic crystals is calculated using exact multipole expansions technique. The Landauers two-terminal formula is used to calculate average of the conductance, its variance and the probability density distribution
Finite elements modelling of scattering problems for flexural waves in thin plates: Application to elliptic invisibility cloaks, rotators and the mirage effect
We propose a finite elements algorithm to solve a fourth order partial
differential equation governing the propagation of time-harmonic bending waves
in thin elastic plates. Specially designed perfectly matched layers are
implemented to deal with the infinite extent of the plates. These are deduced
from a geometric transform in the biharmonic equation. To numerically
illustrate the power of elastodynamic transformations, we analyse the elastic
response of an elliptic invisibility cloak surrounding a clamped obstacle in
the presence of a cylindrical excitation i.e. a concentrated point force.
Elliptic cloaking for flexural waves involves a density and an orthotropic
Young's modulus which depend on the radial and azimuthal positions, as deduced
from a coordinates transformation for circular cloaks in the spirit of Pendry
et al. [Science {\bf 312}, 1780 (2006)], but with a further stretch of a
coordinate axis. We find that a wave radiated by a concentrated point force
located a couple of wavelengths away from the cloak is almost unperturbed in
magnitude and in phase. However, when the point force lies within the coating,
it seems to radiate from a shifted location. Finally, we emphasize the
versatility of transformation elastodynamics with the design of an elliptic
cloak which rotates the polarization of a flexural wave within its core.Comment: 14 pages, 5 figure
Finite wavelength cloaking by plasmonic resonance
We consider cloaking by a coated cylindrical system using plasmonic
resonance, and extend previous quasistatic treatments to include the effect of
finite wavelength. We show that a probe cylinder can still be cloaked at finite
wavelengths, but the cloaking cylinder develops a non-zero scattering
cross-section. We show that this latter effect is dominated by a monopole term
in the case of an ideal (lossless) cloaking material, and by a dipole term in
the case of a realistic (lossy) material. It can be reduced but not eliminated
by variations of geometric or dielectric parameters of the cloaking cylinder
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