Spectral Signature Modification By Application Of Infrared Frequency-selective Surfaces

It is desirable to modify the spectral signature of a surface, particularly in the infrared (IR) region of the electromagnetic spectrum. To alter the surface signature in the IR, two methods are investigated: thin film application and antenna array application. The former approach is a common and straightforward incorporation of optically-thin film coatings on the surface designated for signature modification. The latter technique requires the complex design of a periodic array of passive microantenna elements to cover the surface in order to modify its signature. This technology is known as frequency selective surface (FSS) technology and is established in the millimeter-wave spectral regime, but is a challenging technology to scale for IR application. Incorporation of thin films and FSS antenna elements on a surface permits the signature of a surface to be changed in a deterministic manner. In the seminal application of this work, both technologies are integrated to comprise a circuit-analog absorbing IR FSS. The design and modeling of surface treatments are accomplished using commercially-available electromagnetic simulation software. Fabrication of microstructured antenna arrays is accomplished via microlithographic technology, particularly using an industrial direct-write electron-beam lithography system. Comprehensive measurement methods are utilized to study the patterned surfaces, including infrared spectral radiometry and Fourier-transform infrared spectrometry. These systems allow for direct and complementary spectral signature measurements--the radiometer measures the absorption or emission of the surface, and the spectrometer measures its transmission and reflection. For the circuit-analog absorbing square-loop IR FSS, the spectral modulation in emission is measured to be greater than 85% at resonance. Other desirable modifications of surface signature are also explored; these include the ability to filter radiation based on its polarization orientation and the ability to dynamically tune the surface signature. An array of spiral FSS elements allows for circular polarization conditioning. Three techniques for tuning the IR FSS signature via voltage application are explored, including the incorporation of a pn junction substrate, a piezoelectric substrate and a liquid crystal superstrate. These studies will ignite future explorations of IR FSS technology, enabling various unique applications

Multi-resolution time-domain modelling technique and its applications in electromagnetic band gap enhanced antennas

PhDNewly emerged Electromagnetic Band Gap (EBG) structures possess multiple frequency bands that prohibit wave propagation and such stop bands are basically determined by the periodicity of the structure. Such desirable features make EBG hybrid antenna an interesting topic. Traditional full-wave techniques lack the efficiency to fully cope with the complexity of these hybrid structures, since the periodical elements are often much smaller in size than the accompanying antenna components. The Haar wavelet based Multi-Resolution Time Domain (MRTD) technique provides improved numerical resolution over the conventional Finite-Difference Time-Domain (FDTD) method, as well as simplicity in formulation. One-dimensional, two-dimensional and three-dimensional level-one codes are developed to assist the numerical modelling of the hybrid EBG antennas. An explicit form of Perfectly Matched Layer (PML) configuration is proposed, proved and presented. As a generic approach, its extensions suit every single level of Haar wavelet functions. A source expansion scheme is proposed thereafter. The concept of a multi-band multi-layer EBG hybrid antenna is presented. The theoretical prediction of antenna resonances is achieved through an effective medium model. It has been verified via numerical simulations and measurements. The 3D MRTD code is later applied to simulate such a structure. In addition, EBG enhanced circularly polarized photonic patch antennas have been studied. It is demonstrated that split-resonant rings (SRRs) and the like in EBG antennas can lead to antenna gain enhancement, backward radiation reduction and harmonic suppression. Furthermore, a circularly polarized two-by-two antenna array with spiral EBG elements is presented. The spiral element with ground via is more compact in size than the traditional mushroom structure, which is proven very efficient in blocking unwanted surface wave. Hence it reduces the mutual coupling of the array antenna significantly

Wearable antennas for personal wireless networks.

In this study, we mainly characterize the wearable antenna system for off-body communications with respect to two conventional wireless communication systems as, cellular mobile systems (pes, GSM and UMTS) and wireless local area networks (WLAN). Unlike antennas embedded in portable devices, the complicated bodycentric environment has emerged with special requirements for wearable antennas design, like compact dimensions, light weight and flexible structure, hidden or water proofmg, and most importantly, capable of providing certain radiation shielding into the human body. This thesis aims to fmd an optimum solution to meet the particular requirements ofwearable antenna design. The first part is primarily concerned with characterising the electromagnetic properties of some textile and leather materials. Both insulating and conducting materials are investigated for using as substrate and radiating elements of high perfonnance textile antennas. Then a few of new antenna designs are proposed in the second part. These antennas are made out of textile and leather materials. They are low profIle, planar in geometry, and most importantly, they are capable to provide multi-operations with considerable wide bandwidth. An electromagnetic band gap structure is studied as it can provide a high impedance ground plane for low profIle antennas. The EBG plane can provide a perfect shielding layer for the body, and reduce the radiation toward the body significantly. Furthermore, the EBG plane is able to reduce the detuning of the antenna when placing near the body without serious bandwidth reduction, increase antenna gain and reduce mutual coupling from other devices. The final part carries out a series ofexperiments which can represent the body-centric environment These include bending, washing, wearing, coupling and SAR investigations. Antenna and EBG performances under body worn environment are tested and discussed in this thesis

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow

Contributions au contrôle du faisceau d'antenne réflecteur en utilisant les surfaces sélectives en fréquences et les réseaux réflecteurs

Résumé Les satellites utilisent généralement des antennes construites à base de réflecteurs paraboliques. Pour couvrir une seule zone de la Terre, on utilise deux antennes de taille différente pour les bandes de transmission et de réception. Le contrôle des faisceaux de l'antenne réflecteur nous permettra de combiner les deux antennes tout en maintenant la même largeur de faisceau dans chaque bande. Ce contrôle de faisceaux pourra se faire en utilisant des surfaces sélectives en fréquences (SSF) ou des réseaux réflecteurs (RR). Dans le but de pouvoir utiliser des SSF pour couvrir l'ouverture de l'antenne parabolique, nous avons montré les étapes de la conception d'une SSF bi-bandes multi-couches (à 20 GHz et 30 GHz). Une modification de la géométrie des ouvertures de la cellule est proposée pour diminuer la taille de la cellule en modifiant l'impédance de l'élément. Ainsi, nous avons éloigné les lobes discordants à des fréquences hors des bandes d'intérêt et évité des distorsions dans la bande de fréquences de 30 GHz. Par la suite, nous avons opté pour une SSF en deux couches identiques pour garantir une stabilité de la bande passante en fonction de l'angle d'incidence. Nous avons remarqué des variations brusques des coefficients de transmissions de la SSF à environ 23 GHz. Ces fluctuations sont dues à une excitation d'ondes de surfaces par des modes d'ordres supérieurs. Dans cette étude nous avons supposé que la SSF est de taille infinie. Ce type d'étude nous permet de tenir compte de l'excitation de ces ondes de surfaces. Par ailleurs, l'excitation de ces ondes de surface guidées par le réseau (OSGR) d'éléments ne peut se manifester que lorsque nous étudions une SSF de taille finie. La diffraction des OSGR aux extrémités de la SSF peut modifier le diagramme de rayonnement de l'antenne. Ainsi, nous avons présenté et étudié une méthode numérique pour analyser les SSF de tailles finies en tenant compte des OSGR. D'un autre côté, nous avons présenté les étapes de la conception d'un réseau réflecteur (RR) bi-bandes dont le but est de réfléchir le signal d'une bande de fréquences (dans ce cas 10 GHz) vers la direction spéculaire et de réfléchir le signal de l'autre bande de fréquences (dans ce cas 15 GHz) vers une direction non-spéculaire. Les mesures montrent qu'à 10 GHz le signal est réfléchi vers la direction spéculaire et qu'à 15 GHz le faisceau principal est dirigé vers la direction désirée. Cependant, à 15 GHz, une partie du signal est réfléchie vers la direction spéculaire. Ainsi, nous avons présenté une étude approfondie de ce phénomène de la réflexion dans la direction spéculaire par un RR conçu pour réfléchir vers une direction non-spéculaire. En se basant sur l'hypothèse que ce phénomène est dû à une erreur périodique des phases des éléments du RR, nous avons montré que quand nous ajoutons une erreur périodique linéaire aux phases désirées des éléments, nous obtenons un bon accord entre notre modèle et la simulation par HFSS. Ainsi, ce modèle simple nous a permis d'estimer les directions des lobes indésirables dues à cette erreur. En plus, une étude de l'amplitude de cette réflexion spéculaire en fonction de la couverture du RR par les patchs métalliques est présentée.----------Abstract The antenna systems in satellites are generally based on parabolic reflectors. To cover a single region of the Earth with two distant frequency bands, two different sized antennas are used. The beam control of the aperture antenna would let us use the two different frequencies with the same parabolic antenna system and maintain the same beamwidth for the two frequency bands. This beam control can be done using frequency selective surfaces (FSS) or reflectarrays (RA). In order to be able to use frequency selective surfaces to cover the aperture of the parabolic antenna, we show the steps to study a dual-band and multi-layer frequency selective surface (at 20 GHz and 30 GHz). By decreasing the cell size by changing the geometry of the elements we have delayed in frequency the appearance of the grating lobes and we avoided distortions in the frequency band of 30 GHz. Thereafter, we chose a two-layer frequency selective surfaces to ensure stability of the bandwidth as function of angle of incidence. We noticed an abrupt variation of the transmission coefficients of the frequency selective surface at about 23 GHz. These fluctuations are the effect of the surface waves excited by higher order modes. In this study, we assume that the frequency selective surface is periodic and has an infinite size. This kind of study allows us to take into account the excitation of these surface waves. Furthermore, the excitation of the array guided surface wave can occur also when we study a finite size FSS. The diffraction of these surface waves at the edges of the finite frequency selective surface may modify the radiation pattern of the antenna. Thus, we are presenting a numerical method to analyze large finite size frequency selective surfaces taking into account the array guided surface waves. On the other hand, we also present the steps to design a dual-band RA to reflect the signal of a frequency band (at 10 GHz) to the specular direction and to reflect the signal of the other band frequencies (at 15 GHz) to an off-specular direction. The measurements show that the 10 GHz signal is reflected to the specular direction and the main beam at 15 GHz is reflected in the desired off-specular direction. However, at 15 GHz, part of the signal is still reflected in the specular direction. Thereby, we present a thorough study of the specular reflection by a RA designed to reflect to a non-specular direction. Based on the assumption that this phenomenon is given by a periodic error of the phases of the RA elements, we show that when we add a linear periodic error to the desired phases, we get a good agreement between our model and the HFSS simulation. Thus, this simple model allows us to estimate the directions of undesirable sidelobes. In addition we present a study of the magnitude of the specular reflection as a function of the coverage of the RA by metallic patches

High Impedance Surface – Electromagnetic Band Gap (HIS-EBG) Structures for Magnetic Resonance Imaging (MRI) Applications

High Impedance Surface – Electromagnetic Band Gap (HIS-EBG) structures are one class of Metamaterials with unique and useful electromagnetic properties. This thesis proposes the first application of EBG structures for Magnetic Resonance Imaging (MRI) applications, with the aim of improving effectiveness of coils in creating RF magnetic flux density inside the patient or a phantom. The anti-phase currents in the metallic ground planes placed underneath transmit RF coils for ultrahigh field MRI represent the main reason for the reduction in RF magnetic flux density above these coils (inside the load). In addition, they support the propagation of surface waves which radiate from edges and corners wasting power in the back hemisphere. The objective of this thesis is to investigate the potential of improving the efficiency of a well-established RF coil for 7 Tesla MRI by replacing the standard ground planes with specially designed EBG structures which exhibit novel electromagnetic properties: The reflection of such structures exhibits a frequency range over which an incident electromagnetic wave does not experience a phase reversal, and the image currents appear in-phase rather than out of phase as they do on the standard ground planes. Due to this, the EBG structure is termed an artificial magnetic conductor. Furthermore, it suppresses the propagation of surface waves. In this thesis, novel EBG structures are proposed and fabricated, and their electromagnetic properties are characterized analytically, numerically, and are validated by measurements. The RF coil backed by our proposed EBG ground planes exhibits improvement in the magnetic flux density inside phantoms compared to the case when it is backed by conventional ground planes of the same dimensions. A novel multilayer offset stacked polarization dependent EBG structure is designed to work as a soft surface with anisotropic surface impedance. The designed structure solves the problem of the limited space available in MRI magnet bores. The RF coil backed by the proposed soft surface exhibits stronger magnetic field inside the phantom, while the electric field and the specific energy absorption rate values are reduced.High Impedance Surface – Electronic Band Gap (HIS-EBG) Strukturen für den Einsatz in der Magnetoresonanz-Tomographie (MRT) High Impedance Surface – Electronic Band Gap (HIS-EBG) Strukturen bilden eine Klasse von Metamaterialien mit einzigartigen elektromagnetischen Eigenschaften, welche nicht ohne weiteres in der Natur vorkommen. In dieser Arbeit werden zum ersten Mal EBG Strukturen für den Einsatz in Ultra-Hochfeld Magnetresonanz-Tomographie Anwendungen vorgeschlagen, mit dem Ziel die Effektivität von Spulen, welche für die Erzeugung von hochfrequenten magnetischen Flussdichten in Patienten oder Phantomen verwendet werden, zu erhöhen. Gegenphasige Ströme in den metallischen Masseflächen unterhalb der HF Sende-Spulen sind der Hauptgrund für die Reduzierung der hochfrequenten magnetischen Flussdichten oberhalb dieser Spulen. Ferner kommt es zur Anregung von Oberflächenwellen auf den metallischen Masseflächen und zur Abstrahlung an den Kanten und Ecken, wodurch Leistung in eine unerwünschte Richtung abgestrahlt wird. Das Ziel dieser Arbeit ist die Untersuchung der Möglichkeiten zur Verbesserung des Wirkungsgrads von gängigen HF Spulen für 7 Tesla MRT, bei welchen die Standard- Massefläche durch speziell entworfene EBG Strukturen ersetzt wurde. Bei der Reflektion an solchen Strukturen erfährt die einfallende elektromagnetische Welle in einem bestimmten Frequenzbereich keine Umkehrung der Phase. Im Gegensatz zur Standard-Massefläche, in welcher gegenphasige Ströme entstehen, sind die Ströme in der EBG Struktur gleichphasig. Auf Grund dessen werden die EBG Strukturen als künstliche magnetische Leiter bezeichnet. Des Weiteren wird die Ausbreitung von Oberflächenwellen in EBG Strukturen unterdrückt. In dieser Arbeit, werden einige neuartige EBG Strukturen vorgestellt. Die elektromagnetischen Eigenschaften dieser Strukturen werden sowohl analytisch als auch nummerisch beschrieben und messtechnisch validiert. Die HF Spulen über der EBG Struktur weisen, im Vergleich zum Aufbau über einer herkömmlichen Massefläche, eine deutlich erhöhte magnetische Flussdichte im inneren des Phantoms auf. Des Weiteren wurde eine neuartige, versetzt aufgebaute und polarisationsabhängige Multilagen-EBG Struktur entworfen mit reduzierten Abmessungen um als anisotrope „Soft“-Oberflächenimpedanz fungieren zu können. Die HF Spule über dieser vorgeschlagenen „Soft“ Oberflächenimpedanz führt im inneren des Phantoms zu einer Erhöhung der magnetischen Feldstärke, wobei die Elektrische Feldstärke und die Spezifische Absorptionsrate reduziert werden

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Flight Mechanics/Estimation Theory Symposium, 1992

This conference publication includes 40 papers and abstracts presented at the Flight Mechanics/Estimation Theory Symposium on May 5-7, 1992. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Nonlinear data analysis of the CMB

Das kosmologische Prinzip der Homogenität und statistischen Isotropie des Raumes ist eine fundamentale Annahme der modernen Kosmologie. Auf dieser Basis wird die Existenz einer inflationären Phase im jungen Universum postuliert, welche wiederum primordiale Gaußverteilte Fluktuationen vorhersagt, welche sich im kosmischen Mikrowellenhintergrund als Temperatur- und Polarisationsanisotropien manifestieren. Die Grundidee meiner Arbeit war die Weiterentwicklung einer modellunabhängigen Untersuchungsmethode, welche die Gauß’sche Hypothese für die Dichtefluktuationen testet, wobei die Gaußianität eines Ensembles mit der Zufallsverteilung der Fourier Phasen im Phasenraum definiert wird. Die Methode basiert auf einer nichtlinearen Datenanalyse mit Hilfe von Surrogatkarten, welche die linearen Eigenschaften eines Datensatzes imitieren. Im Rahmen der Surrogatmethode habe ich unter Verwendung zweier verschiedener Bildanalyseverfahren, nämlich den Minkowski Funktionalen und den Skalierungsindizes, beide sensitiv auf Korrelationen höherer Ordnung, Karten der kosmischen Mikrowellenhintergrundstrahlung des WMAP und des Planck Experimentes auf skalenabhängige Phasenkorrelationen untersucht. Ein Schwerpunkt lag hierbei auf Studien zu hemisphärischen Asymmetrien und zum Einfluss der galaktischen Ebene auf die Resultate. Aus der Analyse der Phasenkorrelationen im Phasenraum entwickelte ich neue Methoden zur Untersuchung von Korrelationen zwischen Statistiken höherer Ordnung im Ortsraum und den Informationen des Phasenraumes. Beide Bildanalyseverfahren detektierten Phasenkorrelationen auf den größten Skalen des kosmischen Mikrowellenhintergrundes in vergleichbarer Ausprägung. Der Einfluss der galaktischen Ebene auf diese Resultate zeigte sich in Cutsky Analysen und beim Vergleichen verschiedener Vordergrundsubtraktionsverfahren innerhalb der zwei Experimente als vernachlässigbar gering. Hemisphärische Anomalien auf den größten Skalen der Hintergrundstrahlung wurden wiederholt bestätigt. Die Parametrisierung von Nicht-Gaußianität durch den fNL-Parameter zeigte sich beim Vergleich von fNL-Simulationen mit experimentellen Daten als unzureichend. In Analysen der Daten mit Hilfe von Bianchi-Modellen zeigten sich Hinweise auf eine nicht-triviale Topologie des Universums. Die Resultate meiner Arbeit deuten auf eine Verletzung des standardmäßigen Single Field Slow-Roll Modells für Inflation hin, und widersprechen den Vorhersagen von isotropen Kosmologien. Meine Studien eröffnen im Allgemeinen neue Wege zu einem besseren Verständnis von Nicht-Gauß'schen Signaturen in komplexen räumlichen Strukturen, insbesondere durch die Analyse von Korrelationen der Fourier-Phasen und deren Einfluss auf Statistiken höherer Ordnung im Ortsraum. In naher Zukunft können die Polarisationsdaten des Planck Experimentes weiteren Aufschluss über die Anomalien der kosmischen Mikrowellenhintergrundstrahlung bringen. Die Beschreibung des polarisierten Mikrowellenhintergrundes innerhalb einer Phasenanalyse wäre eine wichtige Ergänzung zu klassischen Studien