Dissertations / Theses: 'Electromagnetic waves'

1

Altintas, Ayhan. "Electromagnetic Scattering from a Class of Open-Ended Waveguide Discontinuities." Connect to resource, 1986. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1208793684.

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2

Xie, Zhongqiang. "Fourth-order finite difference methods for the time-domain Maxwell equations with applications to scattering by rough surfaces and interfaces." Thesis, Coventry University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369842.

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3

Ullrich, Stefan [Verfasser]. "Electromagnetic Drift Waves / Stefan Ullrich." Greifswald : Universitätsbibliothek Greifswald, 2011. http://d-nb.info/1015149332/34.

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4

Yip, Chun Keung. "Underwater Communication using Electromagnetic waves." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485947.

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This project was to investigate the EM waves for transmission in seawater with a varied frequency from about 1 MHz up to 40 MHz. Trials were carried out in the laboratory tank, the Albert Dock and the Loch Linnhe. Standalone transmitter and receiver units were constructed for performing the experimental trials. A receiver is used to pick up the signal from the transmitter and the signal was analysed using ,a spectrum analyser. Frequency can be varied outside the transmitter from a lap top by using an optical fiber. Different types of antennae were built and tried in the experiments. In the Albert Dock, the results have shown that EM waves in the range of 1 to 5 MHz is possible to propagate about 100m using a 30W power amplifier. A new antenna design was developed and investigated in the laboratory tank. Results have shown that there is about 30dB gained by implementing the new antenna design. The signal strength can be further improved by 10 dB when the antenna and the signal generator were matched at 10MHz. In the near field, EM waves suffer from high attenuation in seawater but have a low attenuation in the far field. This is due to the generation of EM waves by dipole oscillations of the water molecules within the antenna field which can be used to explain results obtained from trials.

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5

Hajnal, J. V. "Singularities in monochromatic electromagnetic waves." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354452.

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6

Condon, Brian P. "Atmospheric guiding of electromagnetic waves." Thesis, University of St Andrews, 1993. http://hdl.handle.net/10023/14037.

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We propose to alter the propagation conditions experienced by a microwave beam by the generation of a "laser beam atmospheric waveguide". The waveguide is formed by tailored refractive index changes caused by the absorption of a small part of the energy of an annular laser beam. The objective is to increase the microwave radiation field experienced by a target through improved directionality rather than total radiated power from the source. The equations governing the propagation of high power laser beams in the paraxial limit and their interactions (both linear and non-linear) with an absorbing atmosphere are derived and studied. The mechanisms which lead to the formation of the guide and the effects of the propagation environment are considered in detail and the full paraxial form of the thermal blooming wave equation is derived from first principles. Refractive index changes in air caused by the passage of a 1 kW CW CO2 Gaussian laser beam are studied theoretically and both linear and non-linear cases examined. In the linear case, it is predicted that the laser beam produces a refractive index change of greater than 1 part in 10⁵ for a 1 second beam exposure. In the non-linear case, the iterative scheme developed predicts self-interaction and beam break-up after less than 0.5 s. For an annular beam, refractive index changes of 3 parts in 10 are predicted for the linear case. The influence of refractive index fluctuations on microwave radiation is modelled using a ray-tracing algorithm to investigate the behaviour of microwave radiation in an atmospheric waveguide. For a step-index guide of 5 cm radius, there is strong guiding so that even with a small perturbation in refractivity, rays with a wide range of launch angles are trapped. In the case of a guide with a quadratic refractive index profile, small changes in refractive index (1 part in 10⁶) produce weak guiding where only rays with trajectories very close to the optic axis are trapped. As the refractive index change increases, more divergent rays are trapped until a transition to strong guiding occurs at a critical value (changes in refractive index of the order of 1 part in 10⁴). A number of implementations of the waveguiding concept are proposed and evaluated. For the purposes of an experimental verification, a specially designed Annular Beam Director ("ABD") of an on-axis type is tested. Annular laser beams are propagated over short distances in the laboratory and the results presented. Measurements made with a rotating wire laser beam analyser indicate that the ABD performs well. Experiments designed to measure refractive index changes caused by a 1 kW CW CO2 laser beam of Gaussian profile are described. Measurements are made at wavelengths of 633 nm using a specially configured Michelson interferometer and at 3 mm using a millimetre wave quasi-optical FM noise measurement system. Typical results indicate refractive index changes of the order of 1 part in 106 at both the wavelengths considered. The guiding of microwave radiation is verified using a 1 kW CW CO2 annular laser beam, produced by the ABD, into which microwave energy is injected using a small copper reflector located at the centre of the annulus. In one implementation, the microwave energy is coupled out of the guide with a second copper reflector. In a second implementation, the microwave detector imit is located on the optic axis and the laser beam is terminated in an annular beam dump. The results show clear evidence that the high power laser beam forms a waveguide, increasing the amount of microwave radiation reaching the detector by a factor of 1.5.

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Vallon, Henri. "Focusing high-power electromagnetic waves using time-reversal." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC006/document.

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L'objectif de la thèse a été de mettre en place dans un premier temps des modèles analytiques et statistiques permettant d'évaluer les performances d'un système à retournement temporel de fortes-puissances puis de les vérifier grâce à des mesures.Des campagnes de mesures ont alors permis de vérifier les modèles. Des simulations numériques ont aussi montrées les possibilités offertes par un tel système.En parallèle, des travaux sur l'impact des antennes dans une chambre réverbérantes ont été menés afin d'évaluer les performances d'un système ayant plusieurs sorties.Les résultats de thèses ont permis l'élaboration de nouvelles métriques des performances du système.Le développement d'un prototype a nécessité la conception et la réalisation de chacune des branches du système complet.Les premières campagnes de mesures ont permis la validation complète des modèles
A main aspect of this work has been to develop analytical and statistical models of the power efficiency of a time-reversal amplification system (TRAS).It is also important to evaluate the efficiency of a reverberation chamber. This allows quantifying the power received by one or more antenna when the reverberation chamber is excited. This factor is important when considering construction of the most efficient chamber for time-reversal amplification.Measurements assessing the loading effect of antennas in reverberation chambers when the field can be considered diffused were also undertaken. The study focuses on the evaluation of the varying quality factor when adding loaded antennas in the chamber.Another focus of this work is to evaluate the ratios between signals during calibration and focusing phase. An important aspect of the studies presented in this work thus concerns evaluation of the maximum value of the impulse response in a complex propagation system.We also present the power gain of time-reversal techniques and its statistical advantages compared to a classic use of a reverberation chamber.The development of a prototype required the design and implementation of each of the branches of the complete systems.The first measurement campaigns allowed the complete validation of the models

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8

DeWitt, Brian Thomas. "Analysis and measurement of electromagnetic scattering by pyrimidal and wedge absorbers /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487265143144813.

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9

Teixeira, Elizabeth. "Reflection and transmission of a plane electromagnetic wave on a moving boundary between two dielectrics." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050306-154254/.

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Chatzipetros, Argyrios Alexandros. "Sources of localized waves." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-171252/.

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Christie, David C. "Gravitational tidal effects on electromagnetic waves." Thesis, Lancaster University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431471.

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12

Parsi, Nikhil. "Electromagnetic effects on soybeans." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5041.

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Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 2, 2008) Includes bibliographical references.

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Barik, Krushna Chandra. "Generation of low frequency electromagnetic waves in the magnetosphere." Thesis, IIG, 2021. http://library.iigm.res.in:8080/xmlui/handle/123456798/74.

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14

Servin, Martin. "Nonlinear interaction and propagation of gravitational and electromagnetic waves in plasmas." Doctoral thesis, Umeå University, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-122.

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Gravitational waves and electromagnetic waves are important as carriers of energy and information. This thesis is devoted to the study of the propagation and interaction of these waves in plasmas, with emphasis on nonlinear effects and applications within astrophysics.

The physical systems are described by the Einstein-Maxwell-fluid equations or Einstein-Maxwell-Vlasov equations, when a kinetic treatment is required. The small amplitude and high-frequency approximation is employed for the gravitational waves, such that perturbative techniques can be applied and space-time can be considered locally flat, with a gravitational radiation field superimposed on it. The gravitational waves give rise to coupling terms that have the structure of effective currents in the Maxwell equations and an effective gravitational force in the equation of motion for the plasma. The Einstein field equations describe the evolution of the gravitational waves, with the perturbed energy-momentum density of the plasma and the electromagnetic field as a source.

The processes that are investigated are gravitational waves exciting electromagnetic waves in plasmas, altering the optical properties of plasmas and accelerating charged particles. The thesis also deals with the propagation propertities of gravitational and electromagnetic waves, e.g. effects due to resonant wave-particle interactions, plasma inhomogeneties and nonlinear self-interactions. It is also shown that plasmas that are not in thermodynamical equilibrium may release their free energy by emitting gravitational waves.

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15

Ramprecht, Jörgen. "Electromagnetic Waves in Media with Ferromagnetic Losses." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4776.

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The operation of a wide variety of applications in today's modern society are heavily dependent on the magnetic properties of ferromagnetic materials and their interaction with electromagnetic fields. The understanding of these interactions and the associated loss mechanisms is therefore crucial for the improvement and future development of such applications. This thesis is concerned with electromagnetic waves in media with ferromagnetic losses. We model the dynamics of the magnetization of a ferromagnetic material with the nonlinear Landau-Lifshitz-Gilbert (LLG) equation and study stability conditions on static solutions. Furthermore, with the aid of a small signal analysis this equation is linearized around a stable static solution. From this analysis we obtain a small signal permeability, which shows that ferromagnetic material in general are gyrotropic with a resonant frequency behavior similar to that of a Lorentz material. In difference to dielectric Lorentz material, this resonance frequency can be shifted with the aid of a bias field. For a specific bias field we obtain a frequency behavior that mimics that of a material with electric conductivity losses. In terms of losses per unit volume it is then possible to define a magnetic conductivity which is independent of frequency. We treat composite materials built from ferromagnetic inclusions in a nonmagnetic and nonconductinig background material. The composite material inherits the gyrotropic structure and resonant behavior of the single particle. The resonance frequency of the composite material is found to be independent of the volume fraction, unlike dielectric composite materials. For small enough particles, typically around 100 nm, it becomes energetically favorable to form a single domain in the particle, where disturbances in the magnetization can propagate in the form of spin waves. We study the possibility of exciting spin waves and derive a susceptibility that takes spin waves into account. It is found that spin wave resonances are excited in the gigahertz range and this could offer a way to increase the losses in a composite material. We also discuss some concerns regarding stability and causality of effective material parameters for biased ferromagnetic materials. Finally, we discuss the possibility of using magnetic materials in absorbing applications. We analyze the scattering of electromagnetic waves from a metal surface covered with a thin magnetic lossy sheet. It is found that very thin magnetic layers can provide substantial specular absorption over a wide frequency band. However, magnetic specular absorbers, where the waves propagates just a fraction of the wavelength in the material, seem to require a certain amount of ferromagnetic material which make them quite heavy and thereby limit its practical use. On the other hand, for nonspecular absorbers where the waves propagates several wavelengths in the material, the amount of magnetic material required for efficient absorption seems to be substantially less than for specular absorbers. Thus, as nonspecular absorbers, magnetic lossy materials could offer very thin and light designs.
QC 20100906

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16

El, Babli Inas. "Interaction of electromagnetic waves with biological tissue." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq62633.pdf.

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17

Ramprecht, Jörgen. "Electromagnetic waves in media with ferromagnetic losses /." Stockholm : Electromagnetic Engineering, Elektroteknisk teori & konstruktion, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4776.

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18

Osman, Junaidah. "Scattering and nonlinear interaction of electromagnetic waves." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315373.

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19

Shibanuma, Toshihiko. "Dielectric nanostructures for control of electromagnetic waves." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/61390.

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High refractive index dielectric nanoantennas have emerged as a promising unit for improving optical nanodevices by compensating the drawbacks of plasmonic nanoantennas, which have played a key role in nanophotonics to date. The features of high refractive index dielectric nanoantennas, such as low energy losses, excitation of strong magnetic resonances and enhancement of electric field inside and outside the particle, are expected to provide novel methods to manipulate electromagnetic waves in the nanometer scale. In this thesis, we theoretically explore and experimentally demonstrate a variety of nanostructures based on high refractive index dielectric nanoantennas to aim at the efficient and tuneable control of electromagnetic waves in linear and nonlinear manners. Firstly, asymmetric Si dimers are investigated to achieve unidirectional forward scattering with high efficiency. An electric or magnetic dipole mode is excited in each particle constituting the asymmetric dimer at the same wavelength. The interference between these two dipolar modes can direct the scattered field selectively into the forward direction with high scattering efficiency. Secondly, we investigate metasurfaces built of array of Si nanodimers to obtain switching from high transmission to reflection depending on the incident polarization. The different linear polarization direction of the incident light can alter the hybridization modes of the constituent Si dimers and, hence, the effective permittivity and permeability of the metasurface. The resulted overlap and separation of the electric and magnetic dipolar resonances facilitates the control over the switching between high transmission and reflection. Thirdly, asymmetric Si dimers are explored to obtain tuneable control of directional scattering either in the left or right direction from the incident axis. Our theoretical analysis reveals that the electric or magnetic dipoles excited perpendicular to the dimer axis are mainly responsible for the tuneable scattering. Experimental demonstration of the scattering tuneability is carried out along the substrate by using back focal plane techniques combined with a prism coupling setup. Fourthly, we show that the third harmonic generation from a high refractive index dielectric nanoantenna can be significantly improved by adding a metallic component to build a metal-dielectric hybrid nanostructure. In this way, the plasmonic resonance of a Au nanoring can boost the anapole mode excited in a Si nanodisk, strongly enhancing the electric field inside the Si nanodisk. As a result, high third harmonic intensity and conversion efficiency can be achieved even in nanometer scale. Our findings on how we can attain the efficient and tuneable control of electromagnetic waves using high refractive index dielectric nanostructures will contribute to opening the new paths towards the realization of novel optical nanodevices.

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20

Liu, Ning. "Soil and Site Characterization Using Electromagnetic Waves." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26627.

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Success in geotechnical analysis, design, and construction invariably requires that we have proper knowledge and understanding of (1) the strength, (2) the fluid flow properties, and (3) the stress-deformation behavior of the earth materials. These important engineering properties are primarily determined by the components and structure of a soil, which also dictate the soilâ s responses in an electromagnetic field. As a nondestructive technique, the electromagnetic property measurement offers a promising approach to characterize earth materials and identify the effects of changes in environments. However, despite many investigations in the last several decades, the relationship between the frequency-dependent electromagnetic properties of soils and their components and structure are still not well understood. Hence, estimation of engineering properties of a soil in a quantitative way from electromagnetic measurements can be uncertain. In this research several tasks have been accomplished: (1) Development of a physically based model that provides a means of investigating the coupled effects of important polarization mechanisms on soil electromagnetic properties, and a means of relating the electromagnetic properties of a soil to its fines content, clay mineralogy, anisotropy, degree of flocculation and pore fluid chemistry; (2) Proposal of a practically applicable method to determine the volumetric water content, specific surface area and pore fluid salt concentration simultaneously from the dielectric spectrum; (3) Deduction of the wide-frequency electromagnetic properties of a soil by measuring its responses to a step pulse voltage using time domain reflectometry (TDR); (4) Establishment of the relationships between the specific surface area and compressibility, residual shear strength and hydraulic conductivity. This study establishes a framework for quantifying soil engineering properties from their electromagnetic properties. If properly determined and interpreted, the electromagnetic properties can also provide insights into the causes of soil property changes over time and can be very useful in studying the effects of biological factors in geotechnical engineering, a field that may offer great potential for future advances.
Ph. D.

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Parisi, Giuseppe M. S. P. "Propagation of electromagnetic waves in "Fishnet" metamaterials." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3425440.

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Recently, the fabrication and optimization of nano-hole arrays in noble metal layers have attracted much attention both because of the interesting new physics associated with them and for their potential applications in nano-optics and biosensing. In particular nano-hole arrays in metal-dielectric-metal stacks, also known as "fish-net" type structures, are nowadays the best candidates to accomplish some suggestive physical phenomena like negative refractive index. The doctoral thesis summarizes the study of the propagation of electromagnetic waves in periodic structures, namely in Fishnet metamaterials. The EM propagation enables an uncommon property: the negative refraction index. The general aim of the thesis is to study the origin of the negative refraction index and its dependence on the geometric parameters, initially dealing with the basic three-layers fishnet until studying more evolved structures such as a multilayered fishnet structure. Some methods and effective models for the extraction of the complex parameters will be initially considered in the preliminary study. However for a more rigorous investigation, a recent modal method for the analysis of bulk strongly coupled structures (i.e. multilayered fishnet) ,in which also the evanescent modes linked to the metal losses can play a crucial role , will be presented. The FEM method is based on the Elmholts's equation in weak form and it represents a powerful method for the investigation of complex modes, responsible for the negative refraction index, from a more fundamental point of view.
Recentemente la fabbricazione e l'ottimizzazione di nano aperture periodiche attraverso strati di metalli nobili ha riscosso molta attenzione sia per l'interesse verso fenomeni fisici non comuni sia per le potenziali applicazioni alla nano-ottica e alla biosensoristica. In particolare i metamateriali composti da strati metallo-dielettrici sovrapposti e perforati da aperture periodiche, conosciuti come strutture a forma di spina di pesce, sono oggi tra i migliori candidati per studiare alcuni fenomeni fisici non comuni, come la rifrazione ad angolo negativo. La tesi di dottorato riassume lo studio della propagazione delle onde elettromagnetiche in strutture periodiche, in particolare nelle "Fishnet". La propagazione di onde elettromangetiche nelle Fishent genera una proprietà non comune: l"indice di rifrazione negativo. L'obbiettivo principale della tesi è quello di studiare l'origine dell'indice di rifrazione negativo e la sua dipendenza dai parametri geometrici a partire da strutture di base come la Fishnet a tre strati fino a strutture più evolute come la Fishnet a multi strato. Dei metodi e modelli effettivi per l'estrazione dei parametri complessi saranno inizialmente considerati per lo studio preliminale. Tuttavia per un'indagine più rigorosa verrà presentato un recente metodo modale adatto all'analisi di strutture omogenee fortemente accoppiate come le Fishnet a multistrato in cui anche i modi evanescenti, legati alla dissipazione del metallo, possono giocare un ruolo cruciale. Il metodo FEM di analisi modale è basato sull'equazioni di Elmholtz in forma debole e rappresenta un potente metodo di indagine per studiare l'evoluzione dei modi complessi, alla base dell'indice effettivo di rifrazione negativo (parte reale e complessa), da un punto di vista più fondamentale.

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22

Young, André. "Mesh termination schemes for the finite element method in electromagnetics /." Link to the online version, 2007. http://hdl.handle.net/10019/735.

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23

Myung, Noh Hoon. "A high frequency analysis of electromagnetic plane wave scattering by perfectly-conducting semi-infinite parallel plate and rectangular waveguides with absorber coated inner walls /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487267546980859.

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24

Herrera, Martín Antonio. "Wave dark matter as a gravitational lens for electromagnetic and gravitational waves." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/9027/.

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The majority of the matter in the known universe is believed to be in the form of Dark Matter, and its widely accepted description is done by Cold Dark Matter (CDM). Nevertheless, its exact properties and composition are still unknown, and it is one of the most active areas of research in Cosmology. The use of Cold Dark Matter has been successful to describe the general behaviour of Dark Matter at large scales. However, it has encountered problems explaining phenomena at other regimes as on the scale of galaxy halos. Therefore, other models have been proposed over time which are able to retain the reasonable success of CDM on large scales and extent it to other regimes where CDM has problems to explain the observed data. One of such models is Scalar field Dark Matter (SFDM). Its properties allow it to produce similar results at large scales and solve the problems encountered at galactic scales. Nevertheless, the difficulty to obtain direct observations of Dark Matter makes it difficult to give a definitive comparison between the models. Therefore, it is important to study dark matter through different methods of analysis that would allow to increase the validity of its scope, and these methods are constantly being researched. In this work, a particular density profile known as Wave Dark Matter is implemented as a gravitational lens to study its behaviour in the cases where it produces strong lensing of light and of gravitational waves. Analytical functions for the description of a soliton core and a soliton core + NFW tail are applied to a sub-sample of 6 galaxies from The Sloan Lens ACS Survey to constrain the lensing parameters and their relation with the profile. Furthermore, by considering the soliton core to be the main contributor to the mass profile, this is implemented as a lens for the case of the wave approximation and further to describe the major effects of the lens on gravitational waves. It was found that the soliton core is too compact and dense in order to reproduce the observed values of the data for the lensed galaxies. However, adding a NFW tail alleviates the problem and reaches radii and masses within the range reported in the literature, although the size of the NFW tail cannot be properly constrained. Meanwhile for gravitational waves, it was found that the lensing parameters of the soliton core, if they are expected to describe a galaxy, will be such that they are more likely to be observed spaceborne gravitational wave detectors. In summary, therefore, a wave dark matter soliton in combination with a NFW tail is able to represent a galaxy, and the combination of ligh and gravitational waves should give new insight on the validity of the profile as a description of Dark Matter galactic haloes.

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Iskandarani, Saad S. "Electromagnetic wave propagation in anisotropic uniaxial slab waveguide." Ohio : Ohio University, 1989. http://www.ohiolink.edu/etd/view.cgi?ohiou1182437230.

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Ma, Qinglin. "Study of scattering and depolarizaiton of an electromagnetic wave incident upon a slab of random medium using radiative transfer theory /." Thesis, Connect to this title online; UW restricted, 1989. http://hdl.handle.net/1773/5843.

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WILLIAMS, JEFFERY THOMAS. "ELECTROMAGNETIC SCATTERING FROM AND NATURAL RESONANCES OF THE CIRCULAR STRIP." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184194.

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The formulation and calculation of the electromagnetic fields scattered from, and the natural resonances of, a thin, perfectly conducting circular strip mounted on a perfectly conducting ground plane is presented. The fields are excited by an axial electric dipole, oriented normal to the surface of the ground plane. An electric field integral equation is formulated in terms of the induced surface current and solved in closed form in the quasi-static limit as an expansion of Chebyshev polynomials. In addition, the integral equation is solved for the general case by the method of moments (MOM). Numerical results are given which show the excellent agreement between the quasi-static and method of moments solutions. The MOM currents are used to determine the field scattered from the circular strip, in both the frequency and time domains. The frequency domain analysis is applied to the problem of fencing small vertical broadcast antennas. We find that appropriately designed fencing can enhance the ground wave of the antenna, while decreasing the sky wave. In addition, we determine that the radiation efficiency of the dipole is sensitive to the size of the circular strip, and that the radiation efficiency displays resonant behavior when the frequency of operation is near a natural resonance of the circular strip. We, also, calculate the time domain transient scattered fields for different circular strip geometries, using the MOM currents and GTD. By deemphasizing the low frequencies in the transient pulse spectrum, we obtain good agreement between the GTD early time scattering and the transient scattering determined from the MOM formulation. Using the MOM formulation, we determine the natural resonances of the circular strip. These resonances are divided into two classes: the exterior resonances and interior resonances. We show the pole trajectories for the first layer of exterior resonances for a wide range of strip height-to-radius ratios. In addition, we locate strong interior resonances which correspond to TM₀(pq) circular cavity modes. Included in these interior resonances are weakly damped resonances which correspond to the TM₀(p)₀ cavity modes. This is the first known report of these TM₀(p)₀ interior resonances for the circular strip geometry. We find that these resonances dominate the scattering in our problem. Using the transient scattered fields calculated from the MOM formulation as input and output data for a single input, single output identification algorithm, we identify the dominant poles in the scattered fields. We show that these dominant poles are those associated with the TM₀(p)₀ interior resonances of the circular strip. In addition, we show that by using intelligent filtering and source selection, a few resonances with higher damping can also be identified.

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Srikasem, Suthum. "Wave reflection in uniaxially anisotropic media." Ohio : Ohio University, 1987. http://www.ohiolink.edu/etd/view.cgi?ohiou1183062033.

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29

Morozov, Gregory V. "Plane electromagnetic waves in layered periodic dielectric structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ62329.pdf.

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30

Hall, Jan-Ove. "Interaction between Electromagnetic Waves and Localized Plasma Oscillations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4282.

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31

McQuillan, Scott. "Electromagnetic waves in Langmuir Blodgett thin film microstructures." Thesis, Queen Mary, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271335.

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32

Kenney, Mitchell Guy. "The development of metasurfaces for manipulating electromagnetic waves." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6725/.

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The work outlined in this thesis focuses on the development and fabrication of metasurfaces for manipulating electromagnetic waves, with the potential for applications in imaging and holography. Metasurfaces are the Two-Dimensional counterpart of metamaterials, which are artificial materials used to invoke electromagnetic phenomena, not readily found in nature, through the use of periodic arrays of subwavelength ‘meta-atoms’. Although they are a new and developing field, they have already secured a foothold as a meaningful and worthwhile focus of research, due to their straight-forward means of investigating fundamental physics, both theoretically and experimentally - owing to the simplicity of fabrication - whilst also being of great benefit to the realisation of novel optical technologies for real-world purposes. The main objective for the complete manipulation of light is being able to control, preferably simultaneously, the polarisation state, the amplitude, and the phase of electromagnetic waves. The work carried out in this thesis aims to satisfy these criteria, with a primary focus on the use of Geometric phase, or Pancharatnam-Berry phase. The first-principles designs are then used to realise proof-of-concept devices, capable of Circular Conversion Dichroism; broadband simultaneous control of phase and amplitude; and a high-efficiency, broadband, high-resolution hologram in the visible-to-infrared.

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Hatziioannou, John. "The scattering of electromagnetic waves by rough surfaces." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627099.

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Tillema, Nico J. P. "An investigation into underground navigation using electromagnetic waves." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/33823.

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This thesis explores the possibility of measuring the movement of an underground transmitter using electromagnetic waves. The displacement of the transmitter was estimated based on the magnitude and phase of the received electromagnetic wave, using receiver antennas at fixed locations. Electromagnetic wave propagation underground was dependent on the frequency used, soil type, soil moisture content and environmental conditions. An extensive investigation has been conducted in measuring the soil dielectric constant and conductivity. When the sample moisture was increased, its dielectric constant increased, being disperse for clays, but fairly linear for sands. Clays show a higher conductivity. The optimum antennas to use underground were dielectric loaded electric monopole and dipole antennas. A method was developed to predict the admittance of insulated monopole antennas in soil using measured data of the ambient medium.

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Maldonado, Theresa A. "Analysis of electro-optic/gyrotropic biaxial crystals for bulk and waveguide applications." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/15851.

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Reese, Owein. "Homogenization of acoustic wave propagation in a magnetorheological fluid." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-101629.

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Sengers, Lynn H. Ailes. "Particle shape corrections to Twersky's formalism for multiple scattering in a random particulate medium." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-06102009-063037/.

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Sundberg, Garth. "Numerical Modeling of Electromagnetic Scattering in Explosive Granular Media." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/865.

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Terahertz (THz) reflection and transmission spectroscopy is a promising new field with applications in imaging and illicit material detection. One particularly useful application is for the detection of improvised explosive devices (IEDs) which is a favorite weapon of global terrorists. Explosive materials have been shown to have a unique spectral signature in the THz band which can be used to identify the explosives. However, the initial measurements performed on the explosive samples do not account for the modulation of the spectral features by random scattering that will be prevalent with actual samples encountered in applications. The intent of this work is to characterize and quantify the effects of random scattering that may alter the spectral features. Specifically, the effect that a randomly rough surface and granular scattering has on the scattered THz wave (T-Rays) will be investigated and characterized using the Finite-Difference Time-Domain (FDTD) simulation method. The FDTD method is a natural choice for this work as it can handle complicated geometries (i.e., multiple scatterers, arbitrarily rough interfaces, etc.) arbitrary materials (i.e., dispersive media, etc.) and provides broadband frequency data with one simulation pass. First, the effect that the randomly rough surface of the sample explosive has on the extracted spectral signature will be studied using a Monte-Carlo analysis. Then the effect of the complex structure inside the explosive material (the granular scatterers) will be considered. Next, when the physics of the rough surface and granular scattering are understood, a robust method to extract the spectral signature from the reflected T-rays will be developed.

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Naftali, Verena Kashikuka. "Implementation of a reverberation chamber for electro-magnetic compatibility measurements." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2566.

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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017.
This research project focuses on the implementation of a Reverberation Chamber (RC) by the transformation of an existing electromagnetically shielded room. The reverberation chamber is a kind of shielded room designed to create a statistically random internal electromagnetic environment. The reverberating environment makes it possible to obtain high field strengths from a relatively low input power. The electric fields in the chamber have to be stirred to achieve a statistically uniform field. The first part of this thesis presents an overview of reverberation chamber principles and preliminary calculations are done: the lowest usable frequency is estimated to be close to 300 MHz from empirical criteria. Modelling of the statistical environment is then presented, where electromagnetic quantities are characterised by probability density functions (Gaussian, Rayleigh and exponential); correlation issues are also presented. Measurements are performed in the frequency range of 800 MHz – 4 GHz, dictated by the antennas available for this research study. An investigation of cable losses is conducted, followed by a discussion on measurement accuracy. Mechanical stirrers are designed and manufactured. Electromechanical components are selected based on the literature study. Measurements are obtained through an automated setup using MATLAB®. To verify that the RC, with its in-house designed mechanical stirrers, is well-operated, the stirring ratio is experimentally determined. After this first test, an exhaustive investigation of probability density functions is conducted, taking into account correlation issues. Measurements show that the quality factor of the chamber is close to 2000 at 3 GHz, and that 60 independent stirrer positions at 4 GHz can be used for statistical analyses. Finally, the uniformity test is performed with an improved accuracy using frequency stirring. In conclusion, the CPUT RC passes the validation procedure according to the IEC 61000-4-21 standard by generating the required field uniformity within the accepted uncertainty level.

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Ghosh, Sanjay Kumar. "Some problems on propagation of electromagnetic waves in plasma." Thesis, University of North Bengal, 1988. http://hdl.handle.net/123456789/603.

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Park, Young C. (Young Chul) 1960. "A Study of Some Biological Effects of Non-Ionizing Electromagnetic Radiation." Thesis, University of North Texas, 1996. https://digital.library.unt.edu/ark:/67531/metadc278105/.

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The experimental studies of this work were done using a microwave cavity spectrometer, Escherichia coli (E-coli) bacteria, and other peripheral equipment. The experiment consists of two steps. First, a general survey of frequencies from 8 GHz to 12 GHz was made. Second, a detailed experiment for specific frequencies selected from the first survey were further studied. Interesting frequency dependent results, such as unusually higher growing or killing rates of E-coli at some frequencies, were found. It is also concluded that some results are genetic, that is, the 2nd, and 3rd subcultures showed the same growing status as the 1st cultures.

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Schneider, John Brand. "Electromagnetic detection of buried dielectric targets /." Thesis, Connect to this title online; UW restricted, 1991. http://hdl.handle.net/1773/5961.

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Al, Durra Ahmed Abad. "DORT method and selective focusing of UWB electromagnetic waves." Connect to resource, 2005. http://hdl.handle.net/1811/5864.

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Thesis (Honors)--Ohio State University, 2005.
Title from first page of PDF file. Document formattted into pages: contains 23 p.; also includes graphics. Includes bibliographical references (p. 22-23). Available online via Ohio State University's Knowledge Bank.

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44

Glotov, Petr. "Time Reversal of Electromagnetic Waves in Randomly Layered Media." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-02272006-183752/.

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Time reversal is a general technique in wave propagation in inhomogeneous media when a signal is recorded at points of a device called time reversal mirror, gets time reversed and radiated back in the medium. The resulting field has a property of refocusing. Time reversal in acoustics has been extensively studied both experimentally and theoretically. In this thesis we consider the problem of time reversal of electromagnetic waves in inhomogeneous layered media. We use Markov process model for the medium parameters which allows us to exploit diffusion approximation theorem. We show that the field generated by the time reversal mirror focuses at a point of initial source inside of the medium. The size of the focusing spot is of the kind that it is smaller than the one that would be obtained if the medium were homogeneous meaning that the super resolution phenomenon is observed.

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Duffy, Alistair Paul. "Coupling of electromagnetic waves into wires : experiments and simulations." Thesis, University of Nottingham, 1993. http://eprints.nottingham.ac.uk/13658/.

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Electromagnetic Compatibility (EMC) problems may occur in many environments. This Thesis considers a particular sub-set of coupling within shielded enclosures. The actual systems studied are the coupling between a dipole and either one or two rods in a screened room and the effect of a cavity and apertures on a signal travelling along a wire. Experiments are described for the screened room which investigate the repeatability of the measurements and the effects of two closely spaced conductors on the coupling results. The cavity experiments also consider the repeatability of the measurements and the effects of the apertures. Transmission-Line Modelling (TLM) is compared with some other popular modelling methods and generally described. It is applied to the modelling of the experimental systems already discussed. An inherent error associated with the modelling of wires in TLM, manifesting itself as an apparent decrease in the resonant frequency of a wire-like structure, is investigated. The source of the error is deduced and a method of minimising it is proposed. The experimental results are applied to the validation of TLM, and its error correction. Very good comparisons between the experiments and simulations are reported. Correlelograms are investigated as a method of comparing the modelled and experimental results.

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Halabe, Udaya Bhatta. "Condition assessment of reinforced concrete structures using electromagnetic waves." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14245.

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Oates, John H. (John Harvey). "Propagation and scattering of electromagnetic waves in complex environments." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34062.

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Mosquera, Luis G. "Wastewater Disinfection in Enclosed Recirculation Systems with Electromagnetic Waves." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1752.

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Finding the most cost-effective and environmental friendly way to treat and disinfect wastewater has been raising concerns around the world. Failure in performing disinfection of wastewater before returning it to the environment could have terrible consequences to human health and the ecosystem. The risks associated to continue with current practices have led to the creation of stringent regulations. In this research the HYDROPATH technology is tested while attaching a HydroFlow 60i unit to a reactor that works as a closed recirculation system. To determine the feasibility of the HydroFlow 60i unit as an alternative method to chlorine, the EPA method 1306 is used being Escherichia coli the unit of quantification. After performing several experiments modifying parameters such as conductivity and detention time, it was concluded that the HydroFlow 60i unit by itself would not able to replace current disinfection technologies, to meet EPA standards of E. coli removal.

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McCormack, Matthew. "Propagation of electromagnetic waves in spatially dispersive inhomogeneous media." Thesis, Lancaster University, 2014. http://eprints.lancs.ac.uk/74368/.

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Spatial dispersion is the effect where media respond not only to a signal at one particular point, but to signals in an area around that point. While temporal dispersion is a well studied topic, spatial dispersion is relatively unexplored. This thesis investigates the behaviour of electromagnetic waves in spatially dispersive, inhomogeneous media. In particular, two types of inhomogeneity are considered: media formed from two homogeneous regions with a common interface, and those with a periodic structure. For a material made of two homogeneous regions joined together we establish a set of boundary conditions to describe the behaviour of waves at this interface. These boundary conditions are additional to the standard ones provided by Maxwell’s equations. The conditions found are shown to reduce to those established previously by Pekar in the case of a boundary between a spatially dispersive region and a purely temporally dispersive region. The polarisation is also found for a spatially dispersive medium with periodic structure. Numeric solutions are found and non-divergent modes are identified. Analytic solutions are also found for small magnitudes of the inhomogeneity. Most interestingly these results show that, for certain conditions, there exist coupled mode solutions. This is an unusual phenomena which arises as a result of the spatial dispersion in the system.

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Suedan, Gibreel A. "High frequency beam diffraction by apertures and reflectors." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27545.

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Most solutions for electromagnetic wave diffraction by obstacles and apertures assume plane wave incidence or omnidirectional local sources. Solutions to diffraction problems for local directive sources are needed. The complex source point representation of directive beams together with uniform solutions to high frequency diffraction problems is a powerful combination for this. Here the method is applied to beam diffraction by planar structures with edges, such as the half-plane, slit, strip, wedge and circular aperture. Previously used restrictions to very narrow beams and paraxial regions, are removed here and the range of validity increased. Also it is shown that the complex source point method can give a better approximation to broad antenna beams than the Gaussian function. The solution derived for the half-plane problem is uniform, accurate and valid for all beam orientations. This solution can be used as a reference solution for other uniform or asymptotic solutions and is used to solve for the wide slit and complementary strip problems. Uniform solutions for omidirectional sources are developed and extended analytically to become solutions for directive beams. The uniform theory of diffraction is used to obtain uniform solutions where there are no simple exact solutions, such as for the wedge and circular aperture. Otherwise rigorously correct solutions at high frequencies for singly diffracted far fields are used, such as for the half-plane, slit and strip. The geometrical theory of diffraction and equivalent line currents are used to include interaction between edges. Extensive numerical results including the limiting cases; e.g. plane wave incidence, line and point sources are given. These solutions are compared with previous solutions, wherever possible and good agreement is evident Beam diffraction by a wedge with its edge on the beam axis is analysed. This solution completes a previous asymptotic solution which is infinite on the shadow boundaries and inaccurate in the transition regions. Finally, the diffraction by a circular aperture illuminated by normally incident acoustic beam, is derived and the singularity along the axial caustic is removed using Bessel functions and a closed form expression for multiple diffraction is derived.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

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Dissertations / Theses on the topic 'Electromagnetic waves'

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