193 research outputs found
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
Second-Harmonic Generation and Spectrum Modulation by Active Nonlinear Metamaterial
The nonlinear properties of a metamaterial sample composed of double-layer
metallic patterns and voltage controllable diodes are experimentally
investigated. Second harmonics and spectrum modulations are clearly observed in
a wide band of microwave frequencies, showing that this kind of metamaterial is
not only tunable by low DC bias voltage, but also behaves strong nonlinear
property under a small power incidence. These properties are difficult to be
found in normal, naturally occurring materials.Comment: 14 pages, 4 figure
Controlling the Emission of Electromagnetic Sources by Coordinate transformation
The coordinate transformation on the space that contains electromagnetic
sources is studied. We find that, not only the permittivity and permeability
tensors of the media, but also the sources inside the media will take another
form in order to behave equivalently as the original case. It is demonstrated
that, a source of arbitrary shape and position in the free space can be
replaced by an appropriately designed metamaterial coating with current
distributed on the inner surface and would not be detected by outer observers,
because the emission of the source can be controlled at will in this way. As
examples, we show how to design conformal antennas by covering the sources with
transformation media. The method proposed in this letter provides a completely
new approach to develop novel active EM devices
Design and analytically full-wave validation of the invisibility cloaks, concentrators, and field rotators created with a general class of transformations
We investigate a general class of electromagnetic devices created with any
continuous transformation functions by rigorously calculating the analytical
expressions of the electromagnetic field in the whole space. Some interesting
phenomena associated with these transformation devices, including the
invisibility cloaks, concentrators, and field rotators, are discussed. By
carefully choosing the transformation function, we can realize cloaks which are
insensitive to perturbations at both the inner and outer boundaries.
Furthermore, we find that when the coating layer of the concentrator is
realized with left-handed materials, energy will circulate between the coating
and the core, and the energy transmits through the core of the concentrator can
be much bigger than that transmits through the concentrator. Therefore, such
concentrator is also a power flux amplifier. Finally, we propose a spherical
field rotator, which functions as not only a wave vector rotator, but also a
polarization rotator, depending on the orientations of the spherical rotator
with respect to the incident wave direction. The functionality of these novel
transformation devices are all successfully confirmed by our analytical full
wave method, which also provides an alternate computational efficient
validation method in contrast to numerical validation methods.Comment: 22 pages, 3 figure
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
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