Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 24 for “"surface impedance"”.
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Modeling superconductors using surface impedance techniques
… state and is based on calculating surface impedance as a function of temperature, frequency and material parameters (such as the coherence length and the normal state conductivity). The surface impedance calculations apply the Mattis Bardeen and Zimmermann formulations of …
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Frequency selective surfaces with lumped and time-varying loads, variable surface impedance, and multiple screens
… structures can be applied to a limited class of surface geometries. Since the frequency response of a periodic structure is dependent upon the geometry of the surface, a typical approach to changing the response is to modify the geometry. In the past this meant choosing the element shape, such as …
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Optimal Control for an Impedance Boundary Value Problem
… an incoming time harmonic wave is scattered by a surface of an impenetrable obstacle. The reflected wave is determined by the surface impedance of the obstacle. In this paper we will investigate the problem of choosing the surface impedance so that a desired scattering amplitude is achieved. We …
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Non-linear conduction in superconductors
… problem of the magnetic field dependence of the surface impedance of superconductors, with particular reference to tin. In chapter 1 the predictions of the simple theory for the behaviour of the surface impedance for different frequencies and fieid configurations are described and compared with …
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Rigorous Electromagnetic Modeling of Conductor and Substrate Losses for High -Speed Interconnect Structures
… begins with the introduction of the global surface impedance model that enables the representation of the frequency-dependent current distribution inside the conductor cross section in terms of a mathematically equivalent surface impedance relationship. In order to minimize the computational …
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Novel Cladding Designs for Engineering Electromagnetic Scattering
The rapid development of metamaterials and meta surfaces has revolutionized the field of electromagnetic wave manipulation, offering unprecedented control over wave propagation, reflection, and refraction. These engineered materials, characterized by their unique ability to exhibit properties not …
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Sound radiation from perforated plates
… in terms of a continuously distributed surface impedance to represent the holes. This produces a model for the sound radiation from a perforated unbaffled plate. It is found that the radiation efficiency reduces as the perforation ratio increases or as the hole size reduces. An …
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Identification of barriers and least cost paths for autonomous vehicle navigation using airborne LIDAR data
… vehicles. Least cost paths minimize the sum of impedance across a surface. Impedance can be measured by steepness of slope, impenetrable barriers such as vegetation and buildings, fence lines and streams, or other factors deemed important to the vehicle's success at navigating the terrain. This …
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Tensorial Impedance Surfaces for Manipulating Microwaves
Metasurfaces average boundary conditions are often described with a "surface impedance". Tensorial impedance metasurfaces are surfaces where, due to anisotropy, the impedance becomes a 2nd rank tensor. This results in a boundary condition that has greater control over the surface fields than scalar …
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The effects of chromium and manganese on the superconducting density of states of niobium and vanadium
… of smearing of the gap edge is consistant with surface impedance measurements on Nb, and that it can be related to the fact that the density of state at the Fermi energy in Nb lies on the side of a very sharp peak in the density of states.
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Methodologies and Algorithms for Finite Element Analysis of Electromagnetic Devices and Systems
… properties as well as frequency-dependent surface impedance conditions. This model order reduction framework is further enhanced with new models for efficient handling of electrically small geometric features, such as thin wires. Such models, complemented by convenient schemes for the …
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A magnetotelluric study of southern Vancouver Island.
… involve a determination of the electrical subsurface structure of the earth from measurements of the naturally occuring electromagnetic variations at the surface of the earth. In the present work magnetotelluric measurements made at Victoria, B.C. are analyzed. The results are indicative of an …
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Scalable Bundle Design for Massively Parallel Neuronal Recordings <i>In Vivo</i>
… dimensions, low stray capacitance, and enhanced surface impedance of the electrodes, as well as the high signal to noise amplification of the camera electronics. <br></br><br></br> Here the construction of a system to record neural activity is described and its electrical properties are …
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Design of Ultra-wideband Reflectors
… method, the reflector is designed as a metasurface. The TO method amounts to manipulating of electromagnetic waves using an appropriate set of material parameters such that the wave propagation inside the material behaves in a desired manner. We use TO as a means to design an ultra-wideband …
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Wideband Electromagnetic Band Gap (EBG) Structures, Analysis and Applications to Antennas
… via. EBG structures are equivalent to a magnetic surface at the frequency of resonance and thus have very high surface impedance; this makes the EBG structures useful when mounting an antenna close to conducting ground plane, provided the antenna's currents are parallel to the EBG structure. …
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Investigation of the Superconducting Properties of Niobium Radio-Frequency Cavities
… characterized by a marked increase of the surface resistance at high rf fields, in absence of field emission. A low temperature "in-situ" baking under ultra-high vacuum has been successfully applied by several laboratories to reduce those losses and improve the cavity's quality factor. …
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Operational modelling of geomagnetic fields and geomagnetically induced currents
… measured geoelectric fields and magnetotelluric surface impedance responses are also employed. Analysis is done in both the time and frequency domains. Various aspects of this novel empirical approach have been tested using datasets from power networks in four mid-latitude countries, with …
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An Examination of Site Response in Columbia, South Carolina: Sensitivity of Site Response to "Rock" Input Motion and the Utility of Vs(30)
… design response spectra. Site specific subsurface models are developed for four sites in and near Columbia, South Carolina using shear wave velocity measurements from cone penetrometer tests. The four sites are underlain by thin coastal plain sedimentary deposits, overlying high velocity …
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