360 research outputs found
Full-wave parallel dispersive finite-difference time-domain modeling of three-dimensional electromagnetic cloaking structures
A parallel dispersive finite-difference time-domain (FDTD) method for the
modeling of three-dimensional (3-D) electromagnetic cloaking structures is
presented in this paper. The permittivity and permeability of the cloak are
mapped to the Drude dispersion model and taken into account in FDTD simulations
using an auxiliary differential equation (ADE) method. It is shown that the
correction of numerical material parameters and the slow switching-on of source
are necessary to ensure stable and convergent single-frequency simulations.
Numerical results from wideband simulations demonstrate that waves passing
through a three-dimensional cloak experience considerable delay comparing with
the free space propagations, as well as pulse broadening and blue-shift
effects
A Radial-Dependent Dispersive Finite-Difference Time-Domain Method for the Evaluation of Electromagnetic Cloaks
A radial-dependent dispersive finite-difference time-domain (FDTD) method is
proposed to simulate electromagnetic cloaking devices. The Drude dispersion
model is applied to model the electromagnetic characteristics of the cloaking
medium. Both lossless and lossy cloaking materials are examined and their
operating bandwidth is also investigated. It is demonstrated that the perfect
"invisibility" from electromagnetic cloaks is only available for lossless
metamaterials and within an extremely narrow frequency band.Comment: 18 pages, 10 figure
Dispersive Cylindrical Cloaks under Non-Monochromatic Illumination
Transformation-based cylindrical cloaks and concentrators are illuminated
with non-monochromatic waves and unusual effects are observed with interesting
potential applications. The transient responses of the devices are studied
numerically with the Finite-Difference Time-Domain method and the results are
verified with analytical formulas. We compute the effective bandwidth of
several cloaking schemes as well as the effect of losses on the performance of
the structures. We also find that narrowband behavior, frequency shift effects,
time delays and spatial disturbances of the incoming waves are dominant due to
the inherently dispersive nature of the devices. These effects are important
and should be taken into account when designing metamaterial-based devices.Comment: 12 pages, 9 figure
FDTD modelling of electromagnetic transformation based devices
PhDDuring this PhD study, several finite-difference time-domain (FDTD) methods were
developed to numerically investigate coordinate transformation based metamaterial
devices. A novel radially-dependent dispersive FDTD algorithm was proposed and
applied to simulate electromagnetic cloaking structures. The proposed method can ac-
curately model both lossless and lossy cloaks with ideal or reduced parameters. It was
demonstrated that perfect “invisibility” from electromagnetic cloaks is only available
for lossless metamaterials and within an extremely narrow frequency band. With a
few modifications the method is able to simulate general media, such as concentrators
and rotation coatings, which are produced by means of coordinate transformations
techniques. The limitations of all these devices were thoroughly studied and explo-
red. Finally, more useful cloaking structures were proposed, which can operate over a
broad frequency spectrum.
Several ways to control and manipulate the loss in the electromagnetic cloak ba-
sed on transformation electromagnetics were examined. It was found that, by utili-
sing inherent electric and magnetic losses of metamaterials, as well as additional lossy
materials, perfect wave absorption can be achieved. These new devices demonstrate
super-absorptivity over a moderate wideband range, suitable both for microwave and
optical applications.
Furthermore, a parallel three-dimensional dispersive FDTD method was introdu-
ced to model a plasmonic nanolens. The device has its potential in subwavelength
imaging at optical frequencies. The finiteness of such a nano-device and its impact
on the system dynamic behaviour was numerically exploited. Lastly, a parallel FDTD
method was also used to model another interesting coordinate transformation based
device, an optical black hole, which can be characterised as an omnidirectional broad-
band absorber
A Review of Metamaterial Invisibility Cloaks
The exciting features of metamaterial in conjunction with transformation optics leads to various applications in the microwave regime with such examples as invisible cloak, frequency selective surfaces (FSS), radomes, etc. The concept of electromagnetic invisibility is very much important in aerospace platform. Hence to study the feasibility of implementation of this concept for stealth, an extensive literature survey of metamaterial cloaks has been carried out and reported in this paper along with the basic concept of cloaking. To make the review more effective, the technical papers are classified into three broad sections viz. mathematical modeling, design and simulations, and fabrications and experimental demonstration. Further the design and simulation is focused on different techniques implemented such as finite difference time domain (FDTD), finite element method (FEM), finite integration technique (FIT), inductor-capacitor representation of metamaterial (LC MTM) etc. The review also reports the methods implemented for analysis of metamaterial cloaks with possibility of application to the specific frequency rang
General equation for directed Electromagnetic Pulse Propagation in 1D metamaterial: Projecting Operators Method
We consider a boundary problem for 1D electrodynamics modeling of a pulse
propagation in a metamaterial medium. We build and apply projecting operators
to a Maxwell system in time domain that allows to split the linear propagation
problem to directed waves for a material relations with general dispersion.
Matrix elements of the projectors act as convolution integral operators. For a
weak nonlinearity we generalize the linear results still for arbitrary
dispersion and derive the system of interacting right/left waves with combined
(hybrid) amplitudes. The result is specified for the popular metamaterial model
with Drude formula for both permittivity and permeability coefficients. We also
discuss and investigate stationary solutions of the system related to some
boundary regimes.Comment: 14 pages, Workshop "Waves in inhomogeneous media and integrable
systems" dedicated to Professor Sergey Leble on the occasion of his 70th
birthday Gda\'nsk University of Technolog
Metamaterial
In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow
Characterization and Measurement of Passive and Active Metamaterial Devices
This document addresses two major obstacles facing metamaterial development: uncertainty in the characterization of electromagnetic field behavior in metamaterial structures and the relatively small operational bandwidth of metamaterial structures. To address the first obstacle, a new method to characterize electromagnetic field behavior in a metamaterial is presented. This new method is a bistatic radar cross section (RCS) measurement technique. RCS measurements are well-suited to measuring bulk metamaterial samples because they show frequency dependence of scattering angles and offer common postprocessing techniques that can be useful for visualizing results. To address the second obstacle, this document characterizes the effectiveness of an adaptive metamaterial design that incorporates a microelectromechanical systems (MEMS) variable capacitor. Applying voltages to the MEMS device changes the resonant frequency of the metamaterial. In this research, computational models show that the size of the adaptive metamaterial unit cell should be increased to improve the responsiveness of the resonant frequency to changes in the MEMS capacitor
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