FFT and multigrid accelerated integral equation solvers for multi-scale electromagnetic analysis in complex backgrounds

textNovel integral-equation methods for efficiently solving electromagnetic problems that involve more than a single length scale of interest in complex backgrounds are presented. Such multi-scale electromagnetic problems arise because of the interplay of two distinct factors: the structure under study and the background medium. Both can contain material properties (wavelengths/skin depths) and geometrical features at different length scales, which gives rise to four types of multi-scale problems: (1) twoscale, (2) multi-scale structure, (3) multi-scale background, and (4) multi-scale-squared problems, where a single-scale structure resides in a different single-scale background, a multi-scale structure resides in a single-scale background, a single-scale structure resides in a multi-scale background, and a multi-scale structure resides in a multi-scale background, respectively. Electromagnetic problems can be further categorized in terms of the relative values of the length scales that characterize the structure and the background medium as (a) high-frequency, (b) low-frequency, and (c) mixed-frequency problems, where the wavelengths/skin depths in the background medium, the structure’s geometrical features or internal wavelengths/skin depths, and a combination of these three factors dictate the field variations on/in the structure, respectively. This dissertation presents several problems arising from geophysical exploration and microwave chemistry that demonstrate the different types of multi-scale problems encountered in electromagnetic analysis and the computational challenges they pose. It also presents novel frequency-domain integral-equation methods with proper Green function kernels for solving these multi-scale problems. These methods avoid meshing the background medium and finding fields in an extended computational domain outside the structure, thereby resolving important complications encountered in type 3 and 4 multi-scale problems that limit alternative methods. Nevertheless, they have been of limited practical use because of their high computational costs and because most of the existing ‘fast integral-equation algorithms’ are not applicable to complex Green function kernels. This dissertation introduces novel FFT, multigrid, and FFT-truncated multigrid algorithms that reduce the computational costs of frequency-domain integral-equation methods for complex backgrounds and enable the solution of unprecedented type 3 and 4 multi-scale problems. The proposed algorithms are formulated in detail, their computational costs are analyzed theoretically, and their features are demonstrated by solving benchmark and challenging multi-scale problems.Electrical and Computer Engineerin

Wave Propagation in Materials for Modern Applications

In the recent decades, there has been a growing interest in micro- and nanotechnology. The advances in nanotechnology give rise to new applications and new types of materials with unique electromagnetic and mechanical properties. This book is devoted to the modern methods in electrodynamics and acoustics, which have been developed to describe wave propagation in these modern materials and nanodevices. The book consists of original works of leading scientists in the field of wave propagation who produced new theoretical and experimental methods in the research field and obtained new and important results. The first part of the book consists of chapters with general mathematical methods and approaches to the problem of wave propagation. A special attention is attracted to the advanced numerical methods fruitfully applied in the field of wave propagation. The second part of the book is devoted to the problems of wave propagation in newly developed metamaterials, micro- and nanostructures and porous media. In this part the interested reader will find important and fundamental results on electromagnetic wave propagation in media with negative refraction index and electromagnetic imaging in devices based on the materials. The third part of the book is devoted to the problems of wave propagation in elastic and piezoelectric media. In the fourth part, the works on the problems of wave propagation in plasma are collected. The fifth, sixth and seventh parts are devoted to the problems of wave propagation in media with chemical reactions, in nonlinear and disperse media, respectively. And finally, in the eighth part of the book some experimental methods in wave propagations are considered. It is necessary to emphasize that this book is not a textbook. It is important that the results combined in it are taken “from the desks of researchers“. Therefore, I am sure that in this book the interested and actively working readers (scientists, engineers and students) will find many interesting results and new ideas

Polarimetric Synthetic Aperture Radar (SAR) Application for Geological Mapping and Resource Exploration in the Canadian Arctic

The role of remote sensing in geological mapping has been rapidly growing by providing predictive maps in advance of field surveys. Remote predictive maps with broad spatial coverage have been produced for northern Canada and the Canadian Arctic which are typically very difficult to access. Multi and hyperspectral airborne and spaceborne sensors are widely used for geological mapping as spectral characteristics are able to constrain the minerals and rocks that are present in a target region. Rock surfaces in the Canadian Arctic are altered by extensive glacial activity and freeze-thaw weathering, and form different surface roughnesses depending on rock type. Different physical surface properties, such as surface roughness and soil moisture, can be revealed by distinct radar backscattering signatures at different polarizations. This thesis aims to provide a multidisciplinary approach for remote predictive mapping that integrates the lithological and physical surface properties of target rocks. This work investigates the physical surface properties of geological units in the Tunnunik and Haughton impact structures in the Canadian Arctic characterized by polarimetric synthetic aperture radar (SAR). It relates the radar scattering mechanisms of target surfaces to their lithological compositions from multispectral analysis for remote predictive geological mapping in the Canadian Arctic. This work quantitatively estimates the surface roughness relative to the transmitted radar wavelength and volumetric soil moisture by radar scattering model inversion. The SAR polarization signatures of different geological units were also characterized, which showed a significant correlation with their surface roughness. This work presents a modified radar scattering model for weathered rock surfaces. More broadly, it presents an integrative remote predictive mapping algorithm by combining multispectral and polarimetric SAR parameters

Software for evaluating probability-based integrity of reinforced concrete structures

In recent years, much research work has been carried out in order to obtain a more controlled durability and long-term performance of concrete structures in chloride containing environment. In particular, the development of new procedures for probability-based durability design has proved to give a more realistic basis for the analysis. Although there is still a lack of relevant data, this approach has been successfully applied to several new concrete structures, where requirements to a more controlled durability and service life have been specified. A probability-based durability analysis has also become an important and integral part of condition assessment of existing concrete structures in chloride containing environment. In order to facilitate the probability-based durability analysis, a software named DURACON has been developed, where the probabilistic approach is based on a Monte Carlo simulation. In the present paper, the software for the probability-based durability analysis is briefly described and used in order to demonstrate the importance of the various durability parameters affecting the durability of concrete structures in chloride containing environment

Electromagnetic Waves

This volume is based on the contributions of several authors in electromagnetic waves propagations. Several issues are considered. The contents of most of the chapters are highlighting non classic presentation of wave propagation and interaction with matters. This volume bridges the gap between physics and engineering in these issues. Each chapter keeps the author notation that the reader should be aware of as he reads from chapter to the other

Investigation of nanoenergetic combustion study of aluminum nanoparticles systems on plasmonic grating platform

With renewed interest in energetic materials like aluminum, many fundamental issues concerning the ignition and combustion characteristics at nanoscales remain to be clarified. Aluminum nanoparticles (Al NP) are widely used solid-state fuels in energetic material applications due to the abundance of aluminum and high heat of reaction. The metallic Al core of Al NP must escape an alumina shell to react with oxidizers. The diffusion oxidation mechanism (DOM) of aluminum has been suggested as governing the reaction mechanism, whereby both oxygen and aluminum diffuse through the oxide shell at low heating rates of 10^4-10^6 K/s. However, Al diffusion through the encapsulating shell restricts the reaction rate between the fuel and surrounding oxide. An alternative model is proposed and known as the melt dispersion mechanism (MDM), a rapid thermomechanical mechanism for rapid heating [greater than] 10^6 K/s. This mechanism is driven by the volumetric expansion of rapidly melting Al core which ruptures the oxide shell. MDM has been widely proposed, and we present the first Al NP spallation observed at a particle scale. Plasmonic photothermal heating was needed to facilitate the rapid heating required to initiate the MDM reaction mechanism. A plasmonic grating coupled with an external laser significantly enhances the intensity of photothermal heating experienced by an Al NP. Aluminum, itself, has strong plasmon resonances throughout the visible and ultraviolet spectrum and may be tuned based on Al NP diameter. Our experimental setup encompasses a wide range of available imaging methods to increase the imaging resolution in a table-top optical microscope. A high-resolution camera with a polarization-based scattering method readily identifies whether a particle is metallic or nonmetallic based on the obtained light intensity. Spatiotemporal temperature dependence of Al NP is also observed using fluorescent dyes embedded in a polymer matrix. Finally, the photothermal heating of Al NP in different systems is modeled in COMSOL Multiphysics software using Electromagnetic Waves and Heat Transfer Modules. Based on the simulation, the estimated heating rate can determine the potential mechanism of the observed mechanism. The findings underline the crucial role of heating rates in observing particle spallation through plasmonic enhanced photothermal heating. Combustion of Al NPs is also studied with fluoropolymer and metal-oxide acting as the oxidizer. The current study aims to establish a unified theory accommodating the reaction mechanisms of aluminum particles at micro and nanoscales. The presented works investigate the material constituents starting from individual particle-scale to macro bulk-scale to understand their reaction mechanism better.Includes bibliographical references

Colloidal Monolayers for Concentration Light in Ultra-Thin Semiconductor Layers

Thin film semiconductors are used as photoconductive absorber layers for the development of broadband terahertz generation. Using a femtosecond laser pulse, the generation of a transient increase in the conductivity occurs by photoexciting conduction band electrons in the semiconductor. These thermalize through the emission of terahertz radiation. The route to terahertz generation is not particularly efficient as significant losses come from the absorption in the substrate that is beneath the photoconductive antenna layer. This work explores the application of hexagonally close-packed monolayers of chemically synthesized nanospheres as a potential light concentration method for ultra-thin films of GaAs and black phosphorus that are relevant to terahertz generation. A nanosphere layer can induce an advantageous scattering texture which can increase the effective path length of light transport through the thin film. The nanosphere layer can also induce a significant absorption increase through optical resonances that are caused by the periodic arrangement of hexagonally close-packed spheres. To aid in the study of these effects, we use finite element simulations of absorption in a model GaAs photoconductive layer since GaAs is the present standard photoconductive absorber layer. These simulations enable us to map the absorption resonances in the material as a function of the photoconductive absorber layer thickness and sphere diameter. We are also able to construct the equivalent materials to characterize the optical absorption increases in real, experimental systems. With the aid of these results, we will show that a simple light concentration strategy is able to generate a significant increase in light absorption. Through the increase in light absorption, an improvement of the light-to-terahertz power conversion efficiency is achieved