471 research outputs found
Lateral Shift Makes a Ground-Plane Cloak Detectable
We examine the effectiveness of the ground-plane invisibility cloak generated
from quasiconformal mapping of electromagnetic space. This cloak without
anisotropy will generally lead to a lateral shift of the scattered wave, whose
value is comparable to the height of the cloaked object, making the object
detectable. This can be explained by the fact that the corresponding virtual
space is thinner and wider than it should be. Ray tracing on a concrete model
shows that for a bump with a maximum height of 0.2 units to be hidden, the
lateral shift of a ray with 45 degree incidence is around 0.15 units
Extraordinary surface voltage effect in the invisibility cloak with an active device inside
The electromagnetic field solution for a spherical invisibility cloak with an
active device inside is established. Extraordinary electric and magnetic
surface voltages are induced at the inner boundary of a spherical cloak, which
prevent electromagnetic waves from going out. The phase and handness of
polarized waves obliquely incident on such boundaries is kept in the reflected
waves. The surface voltages due to an electric dipole inside the concealed
region are found equal to the auxiliary scalar potentials at the inner
boundary, which consequently gain physical counterparts in this case
Cylindrical Cloak with Axial Permittivity/Permeability Spatially Invariant
In order to reduce the difficulties in the experimental realizations of the
cloak but still keep good performance of invisibility, we proposed a perfect
cylindrical invisibility cloak with spatially invariant axial material
parameters. The advantage of this kind of TE (or TM) cloak is that only rho and
phi components of mu (or epsilon) are spatially variant, which makes it
possible to realize perfect invisibility with two-dimensional (2D) magnetic (or
electric) metamaterials. The effects of perturbations of the parameters on the
performance of this cloak are quantitatively analyzed by scattering theory. Our
work provides a simple and feasible solution to the experimental realization of
cloaks with ideal parameters
Analysis of photonic crystal filters by the finite-difference time-domain technique
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 76-80).by Bae-Ian Wu.S.M
Cylindrical cloaking at oblique incidence with optimized finite multilayer parameters
We propose multilayer cylindrical invisibility cloaks that are optimized for
oblique incidences through combination of analytic formalism of scattering and
genetic optimization. We show that by using only four layers of homogeneous and
anisotropic metamaterials without large values of constitutive parameters, the
scattering for oblique incidences can be reduced by two orders. Although the
optimization is done at a single incident angle, the cloak provides reduced
scattering over a large range of incident angles
A Rigorous Analysis of Plane-transformed Invisibility Cloaks
The electromagnetic characteristics of plane-transformed invisibility cloaks
are quantitatively studied in this paper. We take elliptical cylindrical cloak
as the example, and use an elliptical cylindrical wave expansion method to
obtain the scattered field. It is demonstrated that an ideal elliptical
cylindrical cloak is inherently visible. Noticeable field scattering and
penetration will be induced when the cloak is exposed directly to an
electromagnetic wave. However, as long as the cloak consists of a perfect
electric conducting lining at the interior surface, perfect invisibility can
still be achieved along the direction parallel to the major axis of the cloak
for transverse magnetic illumination. Another plane-transformed cloak with a
conical geometry is also proposed. The advantage of this cloak is that all the
permittivity and permeability elements are spatially invariant while none of
them is singular. Hence, it is easily realizable with artificially structured
metamaterials. Finally, we show that this kind of cloak can also be used to
cloak objects on a flat ground plane.Comment: 25 pages, 8 figure
Directive Emission Obtained by Coordinate Transformation
We use coordinate transformation theory to realize substrates that can modify
the emission of an embedded source. Simulation results show that with proper
transformation functions the energy radiated by a source embedded in these
space variant media will be concentrated in a narrow beam. The thickness of the
slab achieved with our transformations will no longer be restricted by the
evanescent modes and the source can be placed at any position along the
boundary of the substrate without affecting the radiation pattern. We also
discuss the case where reduced parameters are used, which still performs well
and is physically realizable.Comment: 15 pages, 5 figure
Time domain simulation of electromagnetic cloaking structures with TLM method
This paper was published in Optic 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://dx.doi.org/10.1364/OE.16.006461The increasing interest in invisible cloaks has been prompted in part by the availability of powerful computational resources which permit numerical studies of such a phenomenon. These are usually carried out with commercial software. We report here a full time domain simulation of cloaking structures with the Transmission Line Modeling (TLM) method. We first develop a new condensed TLM node to model metamaterials in two dimensional situations; various results are then presented, with special emphasis on what is not easily achievable using commercial software.This work has been supported in part by the “Ministerio de Educación y Ciencia” of Spain
under research projects No. FIS2004-03273 and FIS2007-63293 cofinanced with FEDER funds of the European Union
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