1,465 research outputs found
Modelling scattering of electromagnetic waves in layered media: An up-to-date perspective
This paper addresses the subject of electromagnetic wave scattering in layered media, thus covering the recent progress achieved with different approaches. Existing theories and models are analyzed, classified, and summarized on the basis of their characteristics. Emphasis is placed on both theoretical and practical application. Finally, patterns and trends in the current literature are identified and critically discussed
Application of iterative techniques for electromagnetic scattering from dielectric random and reentrant rough surfaces
Cataloged from PDF version of article.Stationary [e.g., forward–backward method (FBM)]
and nonstationary [e.g., conjugate gradient squared, quasi-minimal
residual, and biconjugate gradient stabilized (Bi-CGSTAB)]
iterative techniques are applied to the solution of electromagnetic
wave scattering from dielectric random rough surfaces with arbitrary
complex dielectric constants. The convergence issues as well
as the efficiency and accuracy of all the approaches considered
in this paper are investigated by comparing obtained scattering
(in the form of normalized radar cross section) and surface field
values with the numerically exact solution, computed by employing
the conventional method of moments. It has been observed
that similar to perfectly and imperfectly conducting rough surface
cases, the stationary iterative FBM converges faster when applied
to geometries yielding best conditioned systems but exhibits
convergence difficulties for general geometries due to its inherit
limitations. However, nonstationary techniques are, in general,
more robust when applied to arbitrarily general dielectric random
rough surfaces, which yield more ill-conditioned systems. Therefore,
they might prove to be more suitable for general scattering
problems. Besides, as opposed to the perfectly and imperfectly
conducting rough surface cases, the Bi-CGSTAB method and FBM
show two interesting behaviors for dielectric rough surface pro-
files: 1) FBM generally converges for reentrant surfaces when the
vertical polarization is considered and 2) the Bi-CGSTAB method
has a peculiar convergence problem for horizontal polarization.
Unlike the other nonstationary iterative techniques used in this
paper, where a Jacobi preconditioner is used, convergent results
are obtained by using a block-diagonal preconditioner
Proteins in solution: Fractal surfaces in solutions
The concept of the surface of a protein in solution, as well of the interface
between protein and 'bulk solution', is introduced. The experimental technique
of small angle X-ray and neutron scattering is introduced and described
briefly. Molecular dynamics simulation, as an appropriate computational tool
for studying the hydration shell of proteins, is also discussed. The concept of
protein surfaces with fractal dimensions is elaborated. We finish by exposing
an experimental (using small angle X-ray scattering) and a computer simulation
case study, which are meant as demonstrations of the possibilities we have at
hand for investigating the delicate interfaces that connect (and divide)
protein molecules and the neighboring electrolyte solution.Comment: 8 pages, 5 figure
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
Electromagnetic properties of metal-dielectric media and their applications
The main objective of this dissertation is to investigate nano-structured random composite materials, which exhibit anomalous phenomena, such as the extraordinary enhancements of linear and non-linear optical processes due to excitation of collective electronic states, surface plasmons (SP). The main goal is to develop a time and memory efficient novel numerical method to study the properties of these random media in three dimensions (3D) by utilization of multi core processing and packages such as MPI for parallel execution. The developed numerical studies are then utilized to provide a comprehensive characterization and optimization of a surface plasmon enhanced solar cell (SPESC) and to serve as a test bed for enhanced bio and chemical sensing.
In this context, this thesis work develops an efficient and exact numerical algorithm here referred to as Block Elimination Method (BE) which provides the unique capability of modeling extremely large scale composite materials (with up to 1 million strongly interacting metal or dielectric particles). This capability is crucial in order to study the electromagnetic response of large scale inhomogeneous (fractal) films and bulk composites at critical concentrations (percolation). The developed numerical method is used to accurately estimate parameters that describe the composite materials, including the effective conductivity and correlation length scaling exponents, as well as density of states and localization length exponents at the band center. This works reveals, for a first time, a unique de-localization mechanism that plays an important role in the excitation of charge–density waves, i.e. surface plasmons (SP), in metal-dielectric composites. It also shows that in 3D metal-dielectric percolation systems the local fields distribution function for frequencies close to the single particle plasmon resonance is log-normal which is a signature of a metal-dielectric phase transition manifested in the optical response of the composites.
Based on the obtained numerical data a scaling theory for the higher order electric field moments is developed. A distinct evidence of singularities in the surface plasmon density of states and localization length is obtained, correlating with results previously obtained for two dimensional systems. This leads to the main finding of this work; i.e., the delocalization of surface plasmon states in percolating metal-dielectric composite materials is universally present regardless of the dimensionality of the problem.
This dissertation also proposes a new approach toward developing highly efficient inorganic/organic solar cell, by presenting a method for enhancement in the optical absorption and overall cell efficiency. Specifically, the approach improves the operation characteristics of inorganic semiconductor (e.g. Si and a-Si) and organic (P3HT:PCBM) thin film solar cells by integrating a thin, inhomogeneous, metal-dielectric composite (MDC) electrode at the interface between the transparent electrode and active layer. Through numerical simulations, we show that under solar illumination, surface plasmons are excited within the fractal MDC electrode across an extremely broad range of optical frequencies, trapping the incoming light and ensuring an optimal absorption into the active layer of the solar cells. An analytical model is developed to study the I-V characteristics of the cells, providing a pathway toward achieving optimal efficiency and better understanding of the behavior of charge carriers. Using this model, it is shown that including gold MDC electrodes can lead to an enhancement in solar cell power conversion efficiency up to 33% higher compared to the benchmark device
Rigorous direct and inverse design of photonic-plasmonic nanostructures
Designing photonic-plasmonic nanostructures with desirable electromagnetic properties is a central problem in modern photonics engineering. As limited by available materials, engineering geometry of optical materials at both element and array levels becomes the key to solve this problem. In this thesis, I present my work on the development of novel methods and design strategies for photonic-plasmonic structures and metamaterials, including novel Green’s matrix-based spectral methods for predicting the optical properties of large-scale nanostructures of arbitrary geometry. From engineering elements to arrays, I begin my thesis addressing toroidal electrodynamics as an emerging approach to enhance light absorption in designed nanodisks by geometrically creating anapole configurations using high-index dielectric materials. This work demonstrates enhanced absorption rates driven by multipolar decomposition of current distributions involving toroidal multipole moments for the first time. I also present my work on designing helical nano-antennas using the rigorous Surface Integral Equations method. The helical nano-antennas feature unprecedented beam-forming and polarization tunability controlled by their geometrical parameters, and can be understood from the array perspective. In these projects, optimization of optical performances are translated into systematic study of identifiable geometric parameters. However, while array-geometry engineering presents multiple advantages, including physical intuition, versatility in design, and ease of fabrication, there is currently no rigorous and efficient solution for designing complex resonances in large-scale systems from an available set of geometrical parameters. In order to achieve this important goal, I developed an efficient numerical code based on the Green’s matrix method for modeling scattering by arbitrary arrays of coupled electric and magnetic dipoles, and show its relevance to the design of light localization and scattering resonances in deterministic aperiodic geometries. I will show how universal properties driven by the aperiodic geometries of the scattering arrays can be obtained by studying the spectral statistics of the corresponding Green’s matrices and how this approach leads to novel metamaterials for the visible and near-infrared spectral ranges. Within the thesis, I also present my collaborative works as examples of direct and inverse designs of nanostructures for photonics applications, including plasmonic sensing, optical antennas, and radiation shaping
2009 Index IEEE Antennas and Wireless Propagation Letters Vol. 8
This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index
2008 Index IEEE Transactions on Control Systems Technology Vol. 16
This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index
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