L’étude de l’interaction entre une impulsion électromagnétique et un matériau dispersif est un vieux sujet qui remonte au moins au tournant du vingtième siècle avec Sommerfeld et Brillouin. Depuis lors, de nombreux scientifiques ont apporté leur contribution mais il reste un certain nombre de questions, y compris dans des domaines supposés complètement défrichés. Le but de cette thèse est d’aborder, de la manière la plus systématique qui soit, les problèmes les plus emblématiques du domaine de ce qu’il est convenu d’appeler “l’électrodynamique classique dans la matière”. Dans un premier temps, nous avons cherché à répondre à la question simple et fondamentale suivante: un certain nombre de points expérimentaux étant donnés trouver une procédure qui permette d'obtenir un modèle analytique pour la permittivité. Maintenant équipé d’un modèle phénoménologique pour la permittivité, on s’attache à déterminer les caractéristiques essentielles liées à la propagation d’une impulsion électromagnétique dans un milieu arbitrairement dispersif. Après quoi, nous changeons de dimension en nous attaquant aux problèmes tridimensionnels. Nous commençons par l’étude du champ électromagnétique diffusé par une particle chargée ponctuelle oscillant à une fréquence fixe donnée, et placée à côté d’un objet. La dernière partie est une partie plus pratique où l'on aborde des problèmes qui touchent à la technologie. Chercher les résonances de structures ouvertes n’est pas une mince affaire et met en scène des résonances dans le plan complexe. Ici on détermine à la main les QNM (Quasi-Normal Modes) d’une cavité Fabry-Pérot. / The study of the interaction between electromagnetic pulses with dispersive and possible passive materials has a long tradition that can be traced, at least, to the works of Sommerfeld and Brillouin. As time has passed many scientist have contribute to a better understanding of this kind of phenomena. However some well established concepts need to be revisited and some questions remain open. The aim of this thesis is then, to tackle in a very systematic way, some of the most representative problems in this area that has been called “classical electrodynamics in matter”: I) We have developed a mathematical procedure that allows to find analytical models that in the frequency domain fulfils two fundamental physical properties: reality in time domain and causality. II) Our second task is to determine the velocity of an electromagnetic pulse that propagates in a highly dispersive medium. III) The problem of describing the electromagnetic field generated by an oscillating charge and itsinteraction with some dispersive 3D-object is also studied. The first part deals with the pure description of an EM field generated by arbitrary charge density $\rho$ and corresponding current density $j$. Second part is related to the interaction of this polyharmonic EM field and a dispersive object (a sphere). IV) Finding the resonant frequencies and consequently the resonant modes is a well known problem in physics, when the fields are not strictly confined and can leak to the whole universe we can say that we are dealing with Quasi Normal Modes (QNMs). In this thesis we give a brief and straightforward way of deriving the QNMs of a Fabry-Perot cavity.

This thesis describes the investigation carried out on the propagation of radio pulses of frequency 4.73 Mc/s between Grahamstown and Durban. The thesis is divided into two sections - A and B. Section A consists of two chapters. The introductory chapter gives a brief account of how the existence of the ionosphere came to be known. Then follows a description of the different layers of ionization and a review of the theories that have been propounded on the formation of these layers. Chapter 2 deals with the apparatus which includes the transmitter in Grahamstown and the receiving apparatus in Durban. The receiving apparatus comprises: i) a superheterodyne receiver whose gain was high (between 130 and 140 dbs); (ii) a time delay calibrator which could measure time differences of 100 μsec fairly accurately; (iii) a 310 A Tektronix oscilloscope; (iv) a continuously running 35 mm recording camera. Section B is made up of three chapters and is concerned with the actual analysis of the data recorded. The theory of propagation of radio waves in the ionosphere is discussed in Chapter 3. The effects of the magnetic field are neglected since it is found that the error introduced would not make the results unacceptable. Chapter 4 contains the analysis of the data recorded. One summer day and one winter day are discussed in detail in order to obtain the pattern of the diurnal variations for both summer and winter. Some interesting phenomena are also dealt with. An attempt to do ray tracing was successful and the paths followed by a Pedersen and a lower ray from Grahamstown to Durban have been drawn. New topics for further research are discussed in Chapter 5. There are two appendices. Appendix I gives the time delays of all the pulses recorded and their possible identifications. An overall picture of the propagation via the various layers throughout the day (both for summer and for winter is presented in Appendix II.

The forced vibration of a partially delaminated structure such as an aircraft wing can result in catastrophic crack growth. In order to look at the underlying mechanism of the dynamics and failure of the material, a simplified model of a cantilever beam with a single delamination at its free end is considered. We investigate a number of aspects of this system, using mathematical models to gain insight into its behaviour.

This work deals with the fundamental principles of wireless communications in mobile robotics. It introduces overview of the use of different frequency bands for wireless communications needs and control of mobile devices in Czech Republic. It also contains a brief overview of all applicable technologies and available modules that can be used for wireless communication. The theoretical part deals with some of the protocols that were used in the practical part of this work and the manner of wave propagation in buildings. The practical part consisted of a design of our own application to monitor and control the module Mikrotik Routerboard. With this application we have tested and compared two wireless cards of this module.

Digital Elevation Models (DEMs) are computer-generated representations of the earth's surface. These surfaces can be used to predicted Line-of-Sight (LOS) radio propagation. DEM resolution can affect the results of this prediction. This study examines the effect of DEM resolution on accuracy by comparing varied resolution terrain data for a portion of Blacksburg, Virginia using the prediction of ESRI's ArcView® viewshed algorithm. Results show that resolutions between one-meter and thirty-meters have little effect on the aggregate accuracy of the viewshed. / Master of Science

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The Earth's ionosphere is a dynamic environment strongly coupled to the neutral atmosphere, magnetosphere and solar activity. In the context of this research, we restrict our interest to the mid-latitude (a.k.a., sub-auroral) ionosphere during quiet geomagnetic conditions. The Super Dual Auroral Radar Network (SuperDARN) is composed of more than 30 low-power High Frequency (HF, from 8-18 MHz) Doppler radars covering the sub-auroral, auroral and polar ionosphere in both hemispheres. SuperDARN radars rely on the dispersive properties of the ionosphere at HF to monitor dynamic features of the ionosphere. Though originally designed to follow auroral expansion during active periods, mid-latitude SuperDARN radars have observed ground and ionospheric scatter revealing several interesting features of the mid-latitude ionosphere during periods of moderate to low geomagnetic activity. The past 7 years' expansion of SuperDARN to mid-latitudes, combined with the recent extended solar minimum, provides large-scale continuous views of the sub-auroral ionosphere for the first time. We have leveraged these circumstances to study prominent and recurring features of the mid-latitude ionosphere under quiet geomagnetic conditions. First, we seek to establish a better model of HF propagation effects on SuperDARN observations. To do so, we developed a ray-tracing model coupled with the International Reference Ionosphere (IRI). This model is tested against another well established ray-tracing model, then optimized to be compared to SuperDARN observations (Chapter 2). The first prominent ionospheric feature studied is an anomaly in the standard ionospheric model of photo-ionization and recombination. This type of event provides an ideal candidate for testing the ray-tracing model and analyzing propagation effects in SuperDARN observations. The anomaly was first observed in ground backscatter occurring around sunset for the Blackstone, VA SuperDARN radar. We established that it is related to an unexpected enhancement in electron densities that leads to increased refraction of the HF signals. Using the ray-tracing, IRI model, and measurements from the Millstone Hill Incoherent Scatter Radar (ISR), we showed that this enhancement is part of a global phenomenon in the Northern Hemisphere, and is possibly related to the Southern Hemisphere's Weddell Sea Anomaly. We also tested a potential mechanism involving thermospheric winds and geomagnetic field configuration which showed promising results and will require further modeling to confirm (Chapter 3). The second ionospheric feature was a type of decameter-scale irregularity associated with very low drift velocities. Previous work had established that these irregularities occur throughout the year, during nighttime, and equatorward of both the auroral regions and the plasmapause boundary. An initial analysis suggested that the Temperature Gradient Instability (TGI) was responsible for the growth of such irregularities. We first used our ray-tracing model to distinguish between HF propagation effects and irregularity occurrence in SuperDARN observations. This revealed the irregularities to be widespread within the mid-latitude ionosphere and located in the bottom-side F-region (Chapter 4). A second study using measurements from the Millstone Hill ISR revealed that TGI driven growth was possible but only in the top-side F-region ionosphere. We found that initial growth may occur primarily at larger wavelengths, with subsequent cascade to decameter-scale with coupling throughout the F-region (Chapter 5). In summary, the research conducted during this PhD program has established a robust method to analyze quiet-time SuperDARN observations. It also furthered our physical understanding of some prominent features of the mid-latitude ionosphere. It leaves behind a flexible ray-tracing model, multiple online tools to browse SuperDARN data, and a thorough and growing Space Science API providing access to multiple datasets, models and visualization tools. / Ph. D.