Dissertations / Theses on the topic 'Dielectic modes'
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1
Foster, David H. "Fabry-Perot and Whispering Gallery Modes In Realistic Resonator Models." Thesis, view abstract or download file of text, 2006. http://wwwlib.umi.com/cr/uoregon/fullcit?p3211216.
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Thesis (Ph. D.)--University of Oregon, 2006.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 204-213). Also available for download via the World Wide Web; free to University of Oregon users.
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Mansuripur, Masud, Miroslav Kolesik, and Per Jakobsen. "Leaky modes of dielectric cavities." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622709.
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In the absence of external excitation, light trapped within a dielectric medium generally decays by leaking out-and also by getting absorbed within the medium. We analyze the leaky modes of a parallel-plate slab, a solid glass sphere, and a solid glass cylinder, by examining those solutions of Maxwell's equations (for dispersive as well as non-dispersive media) which admit of a complex-valued oscillation frequency. Under certain circumstances, these leaky modes constitute a complete set into which an arbitrary distribution of the electromagnetic field residing inside a dielectric body can be expanded. We provide completeness proofs, and also present results of numerical calculations that illustrate the relationship between the leaky modes and the resonances of dielectric cavities formed by a simple parallel-plate slab, a glass sphere, and a glass cylinder.
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Mansuripur, Masud, Miroslav Kolesik, and Per Jakobsen. "Leaky modes of solid dielectric spheres." AMER PHYSICAL SOC, 2017. http://hdl.handle.net/10150/625335.
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In the absence of external excitation, light trapped within a dielectric medium generally decays by leaking out, and also by getting absorbed within the medium. We analyze the leaky modes of solid dielectric spheres by examining solutions of Maxwell's equations for simple homogeneous, isotropic, linearly dispersive media that admit complex-valued oscillation frequencies. We show that, under appropriate circumstances, these leaky modes constitute a complete set into which an initial electromagnetic field distribution inside a dielectric sphere can be expanded. We provide the outline of a completeness proof, and also present results of numerical calculations that illustrate the close relationship between the leaky modes and the resonances of solid dielectric spherical cavities.
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Tsai, Lu-Min. "Coupled-mode dielectric structure." Thesis, University of Bath, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520820.
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Knoesen, André. "Guided modes in anisotropic dielectric planar waveguides." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/14898.
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Luhaib, Saad Wasmi Osman. "Multi-mode dielectric resonator filters." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/20843/.
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Dielectric resonator (DR) filters are widely used in microwave communications due to their small size and high Q-factor. Multi-mode filters offer a further level of miniaturisation. A new multi-mode dielectric resonator filter is presented in this thesis. The TE11d dual-mode DR offers an 11% size reduction ratio compared with a coaxial air-filled filter with the same unloaded Q-factor (Qu) and about 820 MHz spurious separation from the fundamental frequency 1.95 GHz. Two coupling techniques are applied in the TE11d filter configuration. These are: ceramic puck/probe in contact and etching holes through the ceramic puck for probe installation. A 4th order Chebyshev filter dual-mode DR filter has been simulated and fabricated using each technique. The results show a good agreement between the simulation and measurement with half spurious-free window compared with non-loaded cavity. In the etching method, the spurious-free window and the Qu improved compared with unpatterned ceramic puck. The inline structure filter provides an extra improvement in the spurious window base for the planar configuration. Another approach to the dual-mode DR filter has been studied in this work. A HE11 dual-mode with ceramic puck placed at the base of the cavity presents a good size reduction ratio and acceptable spurious window. The mathematical model shows that transmission zeros (TZs) can be generated in all orientation cases of the inter-resonator coupling hole. The control range of the TZs positions was from 40 MHz from the centre frequency. A good agreement was obtained between the simulation and the measurement results. A triple-mode DR filter with two-piece of the ceramic puck in parallel has been presented. The one cavity approach offers a high Q-factor with 400 MHz suppression. A coaxial probe was used for the input/output coupling and the etching hole through the ceramic puck for inter-resonator coupling. A 3rd order Chebyshev DR filter was simulated and fabricated with two TZs on the upper sideband. The practical results show prospects in application of the filter for miniaturised microwave communications.
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Dufresne, Michel. "Fluid model of dielectric barrier gas discharge." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ36971.pdf.
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Dufresne, Michel 1962. "Fluid model of dielectric barrier gas discharge." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=34520.
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A two-fluid model of dielectric barrier gas discharge is presented in this thesis. The model predicts the physical structure of the gas discharge obtained between two electrodes, when one is covered with a dielectric material: It predicts the distribution of the electron and ion particle densities, electron energy, and electric field strength. It is a self-consistent numerical model, in which the dielectric properties of the dielectric material are included and the geometry of the electrodes is taken into account, thus coupling the charged-particle transport to the electric field.New boundary conditions are developed for the electron gas at the anode; the results indicate that the common boundary conditions frequently used in the literature give solutions with non-physical behavior. The new boundary conditions give solutions with the expected physical behavior.
The equations of the model are formulated numerically using a Galerkin finite element method and solved using the Newton iteration method. New universal matrices for the finite element method are presented which can be used to construct complex finite element matrices, by replacing integrals with matrix products, in a consistent and uniform manner independent of element shape, dimensionality, and order.
Solutions for DC, pulse-waveform and time-harmonic applied electrode voltages for geometries with and without a dielectric barrier are presented. The regulating effect of the dielectric barrier by surface charge accumulation is shown for discharge under constant applied voltage, assuming a static temperature for the electron gas, for the full self-consistent model. Also, simulations of dielectric barrier discharge with applied pulse-waveform voltages are compared with simulations of applied time-harmonic voltages. The results show very similar period-averaged electric fields, electron temperature profiles, charged particle densities, and total conduction current densities. However, a much higher period-integrated ionization rate is obtained from voltage pulse simulations, compared to time-harmonic voltage simulations. Therefore, we obtain a greater reaction rate for an equivalent conduction current, in a period-averaged sense, for a discharge driven by pulse-waveform applied voltages than with time-harmonic applied voltages. Such a difference was not observed for simulations without the dielectric barrier.
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Garnell, Emil. "Dielectric elastomer loudspeakers : models, experiments and optimization." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAE007.
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Les élastomères diélectriques sont des matériaux actifs souples capables de grandes déformations sous chargement électrique. Ils sont constitués d’une fine membrane d’élastomère (en général en silicone ou en acrylique), recouverte de chaque côté par des électrodes souples et étirables. L’ensemble a une épaisseur de l’ordre de 100 microns. Lorsqu’une tension électrique est appliquée entre les électrodes, la membrane se comprime et sa surface peut augmenter de plus de 100%.Ce principe de conversion électromécanique peut être utilisé pour réaliser des haut-parleurs. Des prototypes ont été développés par plusieurs groupes de recherche, et des modèles ont été proposés pour évaluer leurs performances.Une caractéristique intrinsèque des haut-parleurs en élastomères diélectriques est leur nature multiphysique. En effet, le mécanisme d'actionnement est lui-même un couplage entre électrostatique et mécanique; la membrane est très fine et légère, et se couple ainsi fortement à l'acoustique car l’air est lourd par rapport à la membrane; et enfin la résistivité des électrodes engendre un couplage entre l'électro-dynamique et la mécanique.Les modèles proposés jusqu’alors ne considéraient pas l’ensemble de ces couplages, limitant leur utilisation à des estimations qualitatives. Dans cette thèse, un modèle multiphysique de haut-parleurs en élastomères diélectriques est mis en place, afin de permettre l’optimisation de leurs performances acoustiques, en terme de réponse en fréquence, niveau rayonné, et directivité.Les couplages forts entre électrostatique, dynamique membranaire, acoustique, et électrodynamique sont étudiés à l’aide d’un modèle par éléments finis dans FreeFEM. Ce modèle est validé par des comparaisons avec des mesures dynamiques et acoustiques, et ensuite utilisé pour améliorer les performances du prototype, en travaillant sur plusieurs plans : optimisation de l’excitation, filtrage, amortissement, et contrôleDielectric elastomers are soft active materials capable of large deformations when activated by a high voltage. They consist of a thin elastomer membrane (generally made of silicone or acrylic), sandwiched between compliant electrodes. The thickness of the assembly is about 100 microns. When a high voltage is applied between the electrodes, the membrane is squeezed between the electrodes, and increases in area by up to 100%.This electromechanical conversion principle can be used to build loudspeakers. Prototypes have been developed and tested by several research groups, and models have been proposed to estimate their performance.An intrinsic characteristic of dielectric elastomer loudspeakers is their multi-physic nature. Indeed, the actuation mechanism is itself a coupling between electrostatics and mechanics; the membrane is very thin and light, and couples therefore strongly with the surrounding air which is comparatively heavy; and finally the electrode electrical resistivity induces a coupling between electrodynamics and mechanics.The models proposed so far did not consider all of these couplings together, which limited their use to qualitative estimations. In this thesis, a multi-physic model of dielectric elastomer loudspeakers is set-up, in order to optimize their acoustic performances, in terms of frequency response, radiated level, and directivity. The strong couplings between electrostatics, membrane dynamics, acoustics and electrodynamics are studied with a finite element model in FreeFEM. This model is validated by dynamical and acoustical measurements, and then used to improve the performances of the prototype, by working on several levels: optimisation of the excitation, filtering, damping and control
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Chua, Lye Heng. "Triple-mode dielectric loaded cubical cavity filters." Thesis, University of Essex, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397641.
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Khosravi, Heidar. "Theory of electromagnetic modes and spontaneous emission of dielectric media." Thesis, University of Essex, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290440.
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Wang, Henry F. S. (Henry Fu-Sen). "Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 335 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode." Thesis, University of North Texas, 1994. https://digital.library.unt.edu/ark:/67531/metadc279039/.
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The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data.
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Rybak, Michelle (Michelle A. ). "Characterizing dielectric materials with a feedback-based model." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91866.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 54-55).
As signal frequencies continue to increase, conductor surface roughness losses of interconnects are becoming more prominent. There is currently no industry standard for separating the dielectric and conductor losses that appear in PCBs. As part of the thesis work, test vehicles composed of six different dielectric materials were fabricated with different trace widths, copper foil profiles, and oxide surface treatments. A Feedback-Based Model was used to simulate and extract the dielectric and conductor losses from measurements made with the different test vehicles. Simulation software such as MATLAB, Agilent ADS, and Polar Si9000 were utilized. Dielectric material Megtron 4 had the lowest Df of the materials of interest. The Feedback Based Model was able to fit the data well for either low frequencies and high frequencies, but not both. Further, the model was able to model the effects of changes in copper roughness well. Small variations were seen in the extracted Df associated with changes in width of the measurement traces.
by Michelle Rybak.
M. Eng.
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Bernabeu, Jiménez Tomás. "Contribution to the physical interpretation of characteristic mode resonances. Application to dielectric resonator antennas." Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/86177.
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The Theory of Characteristic Modes is being adopted by many research groups around the world in the last decade. This topic and their use in different metallic antenna design is growing very fast. However, most of the applications has been only concentrated on conducting surfaces without any physical knowledge about its limitations and its physical interpretation. As far as dielectric bodies are concerned, there have not been so many published articles. The reason is that there are different integro-differential formulations and the interpretation of their solutions is not as obvious as in conducting bodies. Here, a theoretical interpretation considering loss-less conducting and dielectric bodies is presented.
The conclusions drawn in this thesis will allow us to better understand the solutions of the Theory of Characteristic Modes and their limitations. This is important for antenna engineering. In addition, this analysis will allow to develop a novel method for the design of antennas based on dielectric resonators, DRA. This method is called Substructure based-PMCHWT method, and is based on the implementation of the Schur complements of the method of moments matrix operator. This study permits to optimize the radiation bandwidth in the same analysis process for both, the dielectric and the feed, e.g. slot. Moreover, it allows to understand how the slot behaves in the presence of the dielectric resonator and vice versa. This method can also be used to design DRA using low permittivities. This is important in the design of DRA because the feed perturbs the system and produces a shift in the resonances of the characteristic modes. So, therefore, by considering the feed system in the characteristic modes analysis a more realistic results than a conventional analysis is obtained. On the other hand, the resonances of the characteristic modes at low permittivities are displaced from what are the natural resonances of the dielectric resonator and also the corresponding S11 resonance. Thus, designing with this new method it can draw new conclusions about the design of DRA using the Theory of Characteristic Modes.En la última década, la teoría de los modos característicos está siendo utilizada por muchos grupos de investigación en todo el mundo. Este tema y su uso en diferentes diseños de antenas metálicas está creciendo muy rápido. Sin embargo, la mayoría de las aplicaciones se han concentrado únicamente en antenas metálicas sin ningún conocimiento físico acerca de sus limitaciones y su interpretación física. En lo que se refiere a cuerpos dieléctricos, no han habido tantos artículos publicados como en metales. La razón es que existen diferentes formulaciones integro-diferenciales y la interpretación de sus soluciones no es tan obvia como en cuerpos metálicos. En esta tesis se presenta una interpretación física de las soluciones de la Teoría de Modos Característicos al considerar cuerpos metálicos y dieléctricos sin pérdidas. Las conclusiones de esta tesis nos permitirán comprender mejor las soluciones de la Teoría de Modos Característicos y sus limitaciones. Esto es importante en ingeniería de antenas. Además, este análisis permitirá desarrollar un nuevo método para el diseño de antenas basadas en resonadores dieléctricos, DRA. Este método está basado en la formulación PMCHWT y la función de Green multicapa utilizada en el método de los momentos (MoM). A este nuevo método se le ha denominado "Substructure Characteristic Mode method", y está basado en la implementación de los complementos Schur sobre las submatrices del operador del MoM. Este estudio permite optimizar el ancho de banda de radiación de un DRA en el mismo proceso de análisis tanto para el dieléctrico como para la alimentación, como por ejemplo una ranura. Además, este método permite comprender como se comporta la ranura en presencia del resonador dieléctrico y viceversa. Este método también puede usarse para diseñar DRA usando permitividades bajas. Esto es importante en el diseño de DRA porque la alimentación perturba el sistema y produce un cambio en las resonancias de los modos característicos. Por lo tanto, al considerar la alimentación en el análisis de modos característicos se obtienen resultados más realistas comparándolos con los obtenidos mediante un análisis convencional. Así, diseñando con el "Substructure Characteristic Mode method" se pueden extraer nuevas conclusiones sobre el diseño de DRA mediante la Teoría de Modos Característicos.
En l'última dècada, la teoria dels modes característics està sent utilitzada per molts grups d'investigació en tot el món. Este tema i el seu ús en diferents dissenys d'antenes metàl·liques està creixent molt ràpid. No obstant això, la majoria de les aplicacions s'han concentrat únicament en superfícies conductores sense cap coneixement físic sobre les seues limitacions i la seua interpretació física. Pel que fa a cossos dielèctrics, no hi ha hagut tants articles publicats com en metalls. La raó és que hi ha diferents formulacions integro- diferencials i la interpretació de les seues solucions no és tan òbvia com en cossos conductors. En esta tesi es presenta una interpretació teòrica considerant cossos conductors i dielèctrics sense pèrdues. Les conclusions d'esta tesi ens permetran comprendre millor les solucions de la Teoria de Modes Característics i les seues limitacions. Açò és important en enginyeria d'antenes. Açò és important en enginyeria d'antenes. A més, esta anàlisi permetrà desenrotllar un nou mètode per al disseny d'antenes basades en ressonadors dielèctrics, DRA. Este mètode està basat en la formulació PMCHWT i la funció de Green multicapa utilitzada en el mètode dels moments (MoM) . A este nou mètode se li ha denominat "Substructure Characteristic Mode method", i està basat en la implementació dels complements Schur sobre les submatrius de l'operador del MoM. Este estudi permet optimitzar l'amplada de banda de radiació d'un DRA en el mateix procés d'anàlisi tant per al dielèctric com per a l'alimentació, com per exemple una ranura. A més, este mètode permet comprendre com es comporta la ranura en presència del ressonador dielèctric i viceversa. Este mètode també pot usar-se per a dissenyar DRA usant baixes permitivitats. Açò és important en el disseny de DRA perquè l'alimentació pertorba el sistema i produïx un canvi en les ressonàncies dels modes característics. Per tant, al considerar l'alimentació en l'anàlisi de modes característics s'obtenen resultats més realistes comparant-los amb els obtinguts per mitjà d'una anàlisi convencional. Així, dissenyant amb el "Substructure Characteristic Mode method" es poden extraure noves conclusions sobre el disseny de DRA per mitjà de la Teoria de Modes Característics.
Bernabeu Jiménez, T. (2017). Contribution to the physical interpretation of characteristic mode resonances. Application to dielectric resonator antennas [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86177
TESIS
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Dods, Steven R. A. "A spectral theory for planar dielectric waveguides." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30690.
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The problem of electromagnetic wave propagation across the junction of two similar planar
dielectric waveguides is analysed, within the Kirchhoff approximation, by expanding the field into transverse variations of all possible modes. It is proven that the expansion can represent any solution for any planar dielectric waveguide. The spectral function is introduced into the representation, and this helps resolve some of the theoretical problems in passing from the limit of closed waveguides to open waveguides. Using the spectral function and the Gel'fand-Levitan integral equation some new exact solutions to novel dielectric planar waveguides can be found. Examples of waveguiding by total internal reflection or by Bragg reflection (which are physically very different processes) can be generated by changing a single parameter in the formulation. Usually the representation
for an open dielectric waveguide requires the matrix spectral function. However the Gel'fand-Levitan reconstruction is defined for scalar spectral functions. A technique for constructing the spectral matrix and the scattering solutions from two spectral functions is demonstrated. This technique uses a variational formulation of a scattering experiment. The connection between a dielectric structure and the characteristics of propagation on it is obscure. However the connection between these characteristics and the spectral function
is much clearer. It is sometimes possible to make predictions about the properties of the waveguide by looking at its spectral function only. Since the connection between the spectral function and the dielectric structure is well established by inverse spectral theory, introducing the spectral function has been of help in establishing the desired connection between the dielectric structure and the characteristics of propagation on it.
Such considerations suggest one of the above waveguides is sensitive to small perturbations
and could be used as an electro-optic modulator. Detailed calculations confirm the hypothesis.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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McPhee, Graeme. "Surface-Bound Plasmonic and Leaky Electromagnetic Modes of Metal-Dielectric Structures." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517370.
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Muir, Keith Ross. "Mixed-mode microsystems for biological cell actuation and analysis." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28879.
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Personalised medicine is widely considered to be the future of global healthcare, where diagnosis, treatment, and potentially even drug development, will become specific to, and optimised for, each individual patient. Traditional population based cell studies suppress the influence of outlier cells that are frequently those of most clinical relevance. Hence single-cell analysis is becoming increasingly important in understanding disease, aiding diagnosis and selecting tailored treatment; but remains the preserve of biomedical laboratories far from the patient. Current instruments depend upon cell-labelling to identify the cell type(s) of interest, which require that these be chosen a-priori and may not be those most clinically relevant. Furthermore, cell-labelling is fundamentally subjective, requiring highly-skilled operators to decide upon the validity of each and every test. Therefore, new test methods need to be developed to enable the widespread adoption of single-cell analysis. The passive electrical properties of biological cells are known to be indicative of the specific cell type, but no technology has demonstrated their comprehensive measurement within a mass-manufacturable device. This work aims to show that biologically meaningful information can be obtained in the form of identifiable “cell signatures” through broadband frequency measurements spanning 100 kHz to 100 MHz that exploit the properties of differential electric fields. This hypothesis is tested through the design, implementation and experimental testing of a dedicated microsystem that integrates two novel designs of electrical sensor within a standard, mass-manufacturable Complementary Metal-Oxide Semiconductor microelectronics technology. One sensor measures the absolute electrical environment above a single sense electrode. The other measures the difference in electrical environment between a pair of electrodes, with view to provide information regarding the suspended cell only, through rejecting the common signal due to its suspending medium. Both sensors are shown capable of detecting individual biological cells in physiological solution, and the differential sensor capable of identifying individually-fixed red blood cells, cervical cancer HeLa cells, and three diameters of homogeneous polystyrene micro-beads of comparable size, all while suspended in physiological saline. These results confirm the hypothesis that differential electric fields provide greater distinction of suspended cells from their environment than existing electrical methods. This finding shows that electrode polarisation arising from proximity to liquids, and particularly physiological media, can be overcome through fully-differential electrical cell sensing. However, misalignment between cells and sensor electrodes limits the sensitivity achieved with the microsystem. Methods to overcome such alignment issues should be investigated in future work, along with higher frequency measurements beyond those presented here.
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Liu, Tong. "Dielectric spectroscopy of very low loss model power cables." Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/8375.
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This research study focuses on the dielectric response of XLPE model power cables that have combinations of homo- and co-polymer insulation with furnace and acetylene carbon black semicon shields. Three dielectric spectroscopy techniques, which are frequency response analyzer and transformer ratio bridge in both frequency domain, and charging/discharging current system in time domain, were jointly used to measure the low loss XLPE cables in the frequency range from 10-4Hz to 104Hz at temperatures from 20°C to 80°C. Degassing effects and thermal ageing effects have also been studied with the spectroscopy techniques. Thermal-electric behaviour and maximum voltages for thermal breakdown have been theoretically simulated for the model cables. Three loss origins of the XLPE cables have been found with different loss mechanisms. Conduction loss due to thermally activated electron/hole hopping dominates the lower frequency range from 10-4Hz to 1Hz; Semicon loss due to its in series resistance with the insulation layer in cable equivalent circuit dominates the higher frequency range from 102Hz to 104Hz; intrinsic polarization loss of the XLPE insulation has dominant flat loss spectra in the mid-frequency range from 1Hz to 102Hz. Degassing was found to decrease the conductivity of the model cables, while thermal ageing greatly increased the conductivity. Thermal-electric simulation results with FEMLAB have shown that the position of maximum field changes from inner to outer insulation boundary under higher applied voltages. A loss mechanism model with mathematical expression for dielectric loss spectrum calculation is finally proposed to explain the total dielectric loss of polymer power cables.
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Lui, Tong. "Dielectric spectroscopy of very low cost model power cables." Thesis, University of Leicester, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519511.
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This research study focuses on the dielectric response of XLPE model power cables that have combinations of homo- and co-polymer insulation with furnace and acetylene carbon black semicon shields. Three dielectric spectroscopy techniques, which are frequency response analyzer and transformer ratio bridge in both frequency domain, and charging/discharging current system in time domain, were jointly used to measure the low loss XLPE cables in the frequency range from 10-4Hz to 104Hz at temperatures from 20°C to 80°C. Degassing effects and thermal ageing effects have also been studied with the spectroscopy techniques. Thermal-electric behaviour and maximum voltages for thermal breakdown have been theoretically simulated for the model cables. Three loss origins of the XLPE cables have been found with different loss mechanisms. Conduction loss due to thermally activated electron/hole hopping dominates the lower frequency range from 10-4Hz to 1Hz; Semicon loss due to its in series resistance with the insulation layer in cable equivalent circuit dominates the higher frequency range from 102Hz to 104Hz; intrinsic polarization loss of the XLPE insulation has dominant flat loss spectra in the mid-frequency range from 1Hz to 102Hz. Degassing was found to decrease the conductivity of the model cables, while thermal ageing greatly increased the conductivity. Thermal-electric simulation results with FEMLAB have shown that the position of maximum field changes from inner to outer insulation boundary under higher applied voltages. A loss mechanism model with mathematical expression for dielectric loss spectrum calculation is finally proposed to explain the total dielectric loss of polymer power cables.
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Rotaru, Andrei. "Novel polar dielectrics with the tetragonal tungsten bronze structure." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4184.
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There is great interest in the development of new polar dielectric ceramics and multiferroic materials with new and improved properties. A family of tetragonal tungsten bronze (TTB) relaxors of composition Ba₆M³⁺Nb₉O₃₀ (M³⁺ = Ga³⁺, Sc³⁺ and In³⁺, and also their solid solutions) were studied in an attempt to understand their dielectric properties to enable design of novel polar TTB materials. A combination of electrical measurements (dielectric and impedance spectroscopy) and powder diffraction (X-ray and neutron) studies as a function of temperature was employed for characterising the dynamic dipole response in these materials. The effect of B-site doping on fundamental dipolar relaxation parameters were investigated by independently fitting the dielectric permittivity to the Vogel-Fulcher (VF) model, and the dielectric loss to Universal Dielectric Response (UDR) and Arrhenius models. These studies showed an increase in the characteristic dipole freezing temperature (T[subscript(f)]) with increase B-cation radius. Crystallographic data indicated a corresponding maximum in tetragonal strain at T[subscript(f)], consistent with the slowing and eventual freezing of dipoles. In addition, the B1 crystallographic site was shown to be most active in terms of the dipolar response. A more in-depth analysis of the relaxor behaviour of these materials revealed that, with the stepwise increase in the ionic radius of the M³⁺ cation on the B-site within the Sc-In solid solution series, the Vogel-Fulcher curves (lnf vs. T[subscript(m)]) are displaced to higher temperatures, while the degree of relaxor behaviour (frequency dependence) increases. Unfortunately, additional features appear in the dielectric spectroscopy data, dramatically affecting the Vogel-Fulcher fitting parameters. A parametric study of the reproducibility of acquisition and analysis of dielectric data was therefore carried out. The applicability of the Vogel-Fulcher expression to fit dielectric permittivity data was investigated, from the simple unrestricted (“free”) fit to a wider range of imposed values for the VF relaxation parameters that fit with high accuracy the experimental data. The reproducibility of the dielectric data and the relaxation parameters obtained by VF fitting were shown to be highly sensitive to the thermal history of samples and also the conditions during dielectric data acquisition (i.e., heating/cooling rate). In contrast, UDR analysis of the dielectric loss data provided far more reproducible results, and to an extent was able to partially deconvolute the additional relaxation processes present in these materials. The exact nature of these additional relaxations is not yet fully understood. It was concluded application of the Vogel-Fulcher model should be undertaken with great care. The UDR model may represent a feasible alternative to the evaluation of fundamental relaxation parameters, and a step forward towards the understanding of the dielectric processes in tetragonal tungsten bronzes.
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Hibberd, Morgan. "Studying low frequency vibrational modes using ultrafast techniques." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/studying-low-frequency-vibrational-modes-using-ultrafast-techniques(4f2da8db-befe-4c37-a6ae-42d069c54dd5).html.
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In this thesis, I report on the investigation of the low frequency vibrational modes in a number of different systems using ultrafast spectroscopic techniques. These consist of biological systems, including the enzyme, morphinone reductase (MR) and the related biomolecules, riboflavin (Rb) and flavin mononucleotide (FMN), as well as non-biological systems, including the semiconductor gallium nitride (GaN) and gold nanoparticles (Au NPs). The term low frequency refers to terahertz (THz) frequencies, where vibrational modes exist at the molecular level, with molecular rotations, lattice vibrations and inter- and intra-molecular vibrations occurring in the THz spectral range. These vibrational modes occur on sub-picosecond timescales and therefore ultrafast techniques utilising femtosecond laser pulses provide a means of studying these modes, and are employed throughout this thesis. The two ultrafast techniques of transient absorption (TA) spectroscopy and terahertz time-domain spectroscopy (THz-TDS) were used. Firstly, a high-repetition rate transient absorption (HRRTA) spectrometer was commissioned to perform pump-probe measurements with an ultraviolet pump and broadband visible probe. The performance of the HRRTA spectrometer was benchmarked using Au NPs and used to investigate the existence of a promoting vibration in MR contributing to the catalysis process, predicted to occur at THz frequencies. Weak oscillations were detected in the charge-transfer absorption band of MR bound to the non-reactive cofactor 1,4,5,6-tetra-hydro-nicotinamide adenine dinucleotide (NADH4), with a frequency of approximately 1.5 THz and provide evidence of the first direct observation of a promoting vibration in an enzyme. To complement the TA measurements, THz-TDS was also used to obtain direct measurements of the absorption at THz frequencies. Due to the challenge of studying water-based biological samples, an initial investigation was performed on a wurtzite GaN wafer, which exhibited optical phonon modes in the THz frequency range that were found to determine the dielectric response of the semi-insulating semiconductor wafer. Use of a non-polar m-plane wafer allowed the anisotropic nature to be observed and values of 9.22 ± 0.02 and 10.32 ± 0.03 for the static dielectric constants were obtained for the THz electric field polarised both perpendicular and parallel to the c-axis of the wurtzite GaN wafer, respectively. Finally, biological studies using THz-TDS were performed with measurements on Rb pellets and films revealing vibrational modes in the THz region. The sharp absorption features were not observed in FMN, despite a small difference in molecular content from Rb, and dehydration was required to reveal small amplitude absorption features. Final measurements on MR and MR-NADH4 films were carried out and evidence of absorption features in the THz frequency range were observed, however further work is required to determine the precise origin of these features.
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Al-Kindi, F. J. "A model for impulse breakdown of SF6̲." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382317.
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Francis, Robert M. "A computer model for the transmission characteristics of dielectric radomes." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23584.
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Approved for public release; distribution unlimited.The electric far field radiation pattern is determined for a uniformly illuminated, linearly polarized circular aperture transmitting through a dielectric radome located in the near field of the aperture. A modified electric field integral equation is solved using the method of moments procedure and the thin shell approximation for dielectrics. The resulting solution was computer coded for ogive and spherical radome shapes. The program is designed in a modular fashion to accommodate the addition of different antenna types, illumination functions, or radome shapes.
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CHAVES, MIRIAM B. F. "ELIMINATION OF ESPURIOS MODES IN FINITE-ELEMENT METHOD OF SOLUTION FOR DIELECTRIC WAVEGUIDES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1994. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8464@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOTrês métodos de eliminação de modos espúrios em soluções de guias de ondas dielétricos, inomogêneos e anisotrópicos, usando formulações variacionais e o Método de Elementos Finitos são analisados. O método das penalidades com a técnica de integração reduzida seletiva é aplicado pela primeira em problemas de Eletromagnetismo. Através da análise de vários exemplos, seus resultados são comparados aos obtidos com o método das componentes transversais devido a Hayata e Koshiba e com o uso de elementos de aresta. A qualidade das aproximações e o desempenho computacional comprovam a eficiência da integração reduzida, que eliminou os principais incovenientes do método das penalidades, mantendo seus atrativos e a simplicidade da implementação. O uso de elementos de aresta também se mostrou uma abordagem atraente embora seus mecanismos de funcionamento ainda não estejam completamente entendidos e apesar da maior complexidade na implementação.
Three methods for elimination of spurious modes from variationally formulated Finite Element solutions of inhomogeneous/anisotropic dieletric waveguides are compared. The Reduced Integration Penalty Method is applied for the first time. To EM wave problems. From the analyses of various examples, the results of this method are compared to those obtained with the Hayeta and Koshiba transversal component method and with the use of edge elements. The quality of the approximations and the computacional performance testify the efficacy of the reduced integration that eliminates the main drawbacks fo the Penalty method while preserving its advantages and simplicity of implementation. The use of edge elements was proven to be a very attractive approach, although its mechanisms are still to be fully understood and its implementation may not always be straightforward in a standard Finite
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Wells, Colin G. "Analysis of shielded rectangular dielectric rod waveguide using mode matching." University of Southern Queensland, Faculty of Engineering and Surveying, 2005. http://eprints.usq.edu.au/archive/00001524/.
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The limit of current technology for mobile base station filters is the multimode filter, in which each cavity supports two (or possibly three) independent degenerate resonances. Shielded dielectric resonators with a rectangular cross-section are useful in this application. In the design of these filters, manufacturers are using software packages employing finite element or finite difference time domain techniques. However, for sufficient accuracy these procedures require large numbers of points or elements and can be very time consuming. Over the last decade research using the mode matching technique has been used to solve this kind of difficulty for various types of filter design and waveguide problems. In this thesis a mode matching method and computer program is developed to calculate the propagation coefficients and field patterns of the modes in a shielded rectangular dielectric rod waveguide. Propagating, complex, evanescent and backward wave modes are included and the work shows the presence of a dominant mode, and other fundamental modes, not previously identified. The effect of the shield proximity on the propagation characteristics and mode spectrum is investigated, together with the limitations on the accuracy of the mode matching method. In addition, the fields within the shielded rectangular dielectric rod waveguide, are used to calculate the attenuation coefficient of the dominant and fundamental modes. The influence on the attenuation coefficient of the proximity of the shield to the rod is also evaluated for these modes and limitations on accuracy are discussed. The calculated numerical results for the propagation and attenuation coefficient values are verified by measurement. The propagation coefficients results are typically within 2% of those measured. Verification of the attenuation coefficient results is achieved by comparing calculated and measured Q at the resonant frequencies of a number of shielded rectangular dielectric rod resonators. The difference between calculated and measured Q values is on average less than 4%. In the absence of a full solution of the shielded rectangular dielectric rod resonator, these results provide useful design information for this structure. In addition, the work reported in this thesis provides a basis for a full electromagnetic solution of this type of resonator. This would encompass the cubic dielectric resonator in a cubical cavity.
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Edquist, Anders. "Electrothermal Design and Analysis of Dielectric TE01-mode Resonator Filters." Thesis, KTH, Elektroteknisk teori och konstruktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166830.
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The use of dielectric resonator filters is very common in the telecommunications industry for applications with demanding filtering requirements. For high power applications in particular, TE01-mode dielectric resonators are often used because of its low losses and excellent peak power handling capabilities. The essence of this work is to great extent focused around the fact that even a small amount of dissipated power can give rise to a large temperature increase if the heat transfer is insufficient. A temperature increase due to self-heating translates into a degradation of filter performance. Understanding the mechanisms behind this degradation is vital in order to compensate for these effects. Computer simulations can successfully be used to characterise the electrical and thermal behaviour of these devices. However, if the filter in question is not properly tuned when running the analysis the results will bring little or no value. This work outlines an efficient filter design flow based on Port Tuning in order to overcome this tuning issue. By carefully studying both a single resonator and a realistic filter example using CFD analysis the heat transfer mechanisms can be quantified and the dominant terms can be identified. Based on these results, a simplified model for the thermal analysis can then be established. A coupled analysis including electromagnetic, thermal and structural analysis is then demonstrated that predicts the performance degradation of the filter response. It is also demonstrated how these effects can be compensated for.Inom telekomindustrin är dielektriska resonatorer vanligt förekommande i filtertillämpningar med krävande prestanda. För högeffekttillampningar i synnerhet används ofta TE01-mod resonatorer på grund av sina låga förluster och utmärkta effekttålighet. Kärnan i detta arbete kretsar kring det faktum att även små effektförluster kan leda till stora temperaturförandringar om värmetransporten är otillräcklig. En sådan temperaturökning på grund av egenuppvarmning yttrar sig i termer av en församring av filterprestandan. En förståelse för mekanismerna bakom denna prestandaförsamring är nödvandig for att lyckas kompensera bort dessa effekter. Datorsimuleringar kan framgångsrikt användas för att karraktärisera dessa komponenter såväl elektriskt som termiskt. Om filtret i fråga däremot inte är trimmat i simuleringen blir värdet av analysen begränsat eller rent av obefintligt. I detta arbete presenteras en effektiv designmetodik baserat på Port Tuning som överbryggar denna trimproblematik. Genom att sedan noggrant studera en ensam resonator och ett mer realistiskt filterexempel med hjälp av CFDanalys kan mekanismerna bakom värmeledningen kvantifieras och de dominerande termerna identifieras. Baserat på dessa resultat kan sedan en förenklad modell för den termiska analysen byggas. Det kan sedan visas hur en kopplad elektromagnetisk-, termisk- och strukturmekanisk analys kan användas fär att prediktera försämringarna av filter-responsen. Det visas också hur dessa effekter sedan kan kompenseras bort.
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Wang, Yu. "Using whey protein gel as a model food to study dielectric heating of salmon." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Thesis/Fall2006/y_wang_121506.pdf.
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Dinulovic, Mirko. "Assessment of dielectric models and their application to polymer matrix composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39105.pdf.
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Miller, Gregory A. "A circuit model for two-path cutoff waveguide dielectric resonator filters." Thesis, Monterey, Calif. : Naval Postgraduate School, 1992. http://handle.dtic.mil/100.2/ADA247785.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 1992.Thesis Advisor: Knorr, Jeffrey B. "March 1992." Includes bibliographical references (p. 58-59). Also available in print.
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Rai, Sheila. "Complex permittivity measurements by multi-mode microwave resonant cavity." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/11517.
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Pang, Shuo. "Whispering gallery modes in quantum dot-embedded dielectric microspheres for tagless remote refractometric sensing." Texas A&M University, 2008. http://hdl.handle.net/1969.1/85998.
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This thesis presents the development of a refractometric sensor based on
quantum dot-embedded polystyrene microspheres. The technique uses optical
resonances within a microsphere, known as Whispering-Gallery Modes (WGMs), which
produce narrow spectral peaks. The basic theory of WGMs is reviewed and specifically
discussed for biosensing application.
The spectral shifts of WGM peaks are sensitive to changes in the local refractive
index. In the experiments, two-photon excited luminescence from the quantum dots
couples into several WGMs within the microresonator. By optimizing the detection area,
the spectral visibility of the WGMs is improved. The spectral shifts are measured as the
surrounding index of refraction changes. The experimental sensitivity is about five times
greater than that predicted by Mie theory.
The sensor element is based on commercially available dielectric microspheres
with a diameter about 10 μm. Thus, the technique is more economic and suitable for
sensing applications, compared to microspheres of 100 μm in size which can only be
made in the laboratory.
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Ng, Matthew Y. K. "Coupling of excited molecules to surface plasmon and other modes of dielectric/metal structures." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11847.
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Song, Yi. "AC conductivity and dielectric constant of systems near the percolation threshold /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu148726754698361.
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Li, Xiang, and Yan Jiang. "Design of a Cylindrical Cavity Resonator for Measurements of Electrical Properties of Dielectric Materials." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-7687.
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In microwave communications, the main aspects for affecting the dielectric losses in the materials are relating to the dielectric properties and the radiation frequencies. Normally, the different dielectric materials will lead to the different losses and reflections for microwave frequencies. To evaluate the dielectric properties from the different materials plays an essential role in the microwave engineering. There are many approaches can be used to measure the dielectric materials, e.g. capacitor methods, transmission line methods, cavity resonator methods, open cavity methods and so on. The cavity resonator method is one of the most popular ways for measuring the dielectric materials. In this thesis, some of the techniques will be reviewed, and the TM010 mode cylindrical cavity resonator with perturbation technique will be used for determining the dielectric properties. The design and measurements will be presented in both simulations and practice. With 1.2GHz cavity resonator, in the simulations, the dielectric permittivity for Teflon is measured as 2.09-0.0023i and 2.12-0.0116 in copper cavity and ferromagnetic cavity. Finally the sample is measured as 3.83-0.12i in practice.
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Chuma, Joseph Monamati. "Compact single and dual mode dielectric resonator filters for mobile communications." Thesis, University of Essex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343502.
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Stanfield, Scott Alan II. "A SPECTROSCOPIC INVESTIGATION OF A SURFACE-DISCHARGE-MODE, DIELECTRIC BARRIER DISCHARGE." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1261582116.
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Curtis, John. "Experimental Verification for Microwave Processing of Materials in a Single Mode Rectangular Resonant Cavity." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/34627.
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The benefits of applying microwave energy to material processing techniques have been well documented and studied. The potential benefits over conventional oven heating include faster processing times, more uniform heating, more consistent product quality, and the possibility of precise control.
The actual implementation of microwave technology has been lacking and the benefits have gone largely unrealized. This is due in part to the temperature dependence of the dielectric loss of many industrial materials such as ceramics and polymers. These materials absorb more microwave energy as they heat, creating uncontrollable heating, often called 'thermal runaway'. The focus of this research is to address this challenge.
The work described here is an experimental program for the microwave processing of specific ceramic rods and polymer tows. The objective of the program is to study the thermal runaway effect, and to provide data which will be used to verify numerical models. Accurate test data are essential to the development of precise, comprehensive models that can be used in applicator design and heating control strategies for thermal runaway materials. The experimental program explores the difficulties of microwave heating and offers solutions to more efficient systems. Successful measurements of power loss and control of thermal runaway are detailed for mullite, alumina, and nylon.Master of Science
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Mrnka, Michal. "Perforovaná dielektrika a dielektrické rezonátorové antény s vyššími módy." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-320299.
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Práce se zabývá buzením vyšších módů v kvádrových a válcových dielektrických rezonátorových anténách pro účely zvýšení zisku. Pomocí numerických simulací jsou studovány vlastnosti a limity anténních prvků. Je zkoumáná vzájemní vazba mezi dielektrickými rezonátorovými anténami pracujícími s vyššími vidy a na základě výsledků je možno usuzovat o vhodnosti těchto prvků k popužití v anténních řadách. V práci je popsán analytický model efektivní permitivity perforovaných dielektrik, který respektuje anizotropní povahu tohoto materiálu. Model je založen na Maxwell Garnettové aproximácií nehomogenních materiálů. Dále jsou studovány povrchové vlny na perforovaných substrátech a je ověřena použitelnost teoretického modelu i v tomto případě. Nakonec jsou studovány dielektrické rezonátorové antény vytvořené pomocí perforací v dielektrickém substrátu a je demonstrováno zhoršení určitých vlastností takových antén.
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Crain, Bruce Richard. "Vector finite element methods for spurious-free solutions of unbounded dielectric and ferrite loaded waveguiding structures." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15501.
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Weathersby, Stephen. "Damping higher order modes in the PEP-II B-factory storage ring collider." Diss., Connect to online resource - MSU authorized users, 2007.
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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2007.Title from PDF t.p. (viewed on August 18, 2009) Includes bibliographic references (p. 175-179). Also issued in print.
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Cherenack, K. H. (Kunigunde Hadelinde). "Modelling of layered cylindrical dielectric resonators with reference to whispering gallery mode resonators." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52942.
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Thesis (MScEng)--University of Stellenbosch, 2002.ENGLISH ABSTRACT: Keywords: Dielectric Resonators, Radial Mode Matching, Whispering Gallery Modes The aim of this investigation was to develop accurate modelling techniques to determine the resonant frequencies of dielectric resonators. These resonators could be simple dielectric posts, rings or combinations of these two. To do this, a radial mode matching technique was implemented and applied to a post resonator, a ring resonator and finally a combination of the two. The resulting method was used to develop a model of a high-Q whispering gallery mode resonator consisting of a post and a ring resonator combination with an spurious free region region.
AFRIKAANSE OPSOMMING: Sleutelwoorde Dielektriese Resoneerders, Radiale Modale-Pas Tegniek, 'Whispering Gallery' Modus Die doel van hierdie navorsing was om 'n akkurate tegniek te ontwikkelom die resonante frekwensie van 'n dielektriese resoneerder vas te stel. Hierdie resoneerders kon eenvoudige resoneerders, ring resoneerders of kombinasies van die twee wees. 'n Radiale Modale-Pas tegniek is vir hierdie doel geïmplementeer en is op 'n eenvoudige resoneerder, 'n ring-resoneerder en kombinasies van die twee toegepas. Hierdie tegniek is dan gebruik om 'n hoë-Q resoneerder te ontwerp wat gebruik maak van 'n 'whispering gallery' modus. In hierdie geval is die resoneerder 'n kombinasie van 'n pil en 'n ring-resoneerder.
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York, Seth. "Microwave Characterization of Printable Dielectric Inks Using Additive Manufacturing Methods." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7385.
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Two methods of dielectric characterization are presented that offer quick and cost-effective solutions for screening complex dielectric material properties. Through Direct-Print Additive Manufacturing (DPAM) methods, a dielectric material of choice is dispensed into a capacitor structure and characterized through 1-port s-parameter measurements. The presented methods use fixtures that are modeled and validated through simulation then implemented in practice. Advanced simulations are performed to gain insights which are used to optimize the dielectric characterization performance of the fixtures. Additional investigations are performed which investigate the durability of the fixture and material within by exposing the combination to rough environmental conditions for an extended duration. The presented capacitor structures are investigated to characterize dielectric materials within the bandwidth of 0.1-15 GHz, saving the time and effort required in using multiple dielectric characterization methods that cover the same bandwidth. Both methods are compared based on the results for each method achieved in practice while considering the process required perform each method. The pros and cons of the presented characterization methods are weighed which highlights the key aspects for successfully characterizing dielectric materials with each method as well as revealing the potential limitations associated with each.
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Schneck, William Carl III. "Multi-Physics Model of a Dielectric Barrier Discharge Flow Control Actuator with Experimental Support." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/65004.
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This dissertation presents an experimentally supported multi-physics model of a dielectric barrier discharge boundary layer flow control actuator. The model is independent of empirical data about the specific behavior of the system. This model contributes to the understanding of the specific mechanisms that enable the actuator to induce flow control.
The multi-physics numerical model couples a fluid model, a chemistry model, and an electrostatics model. The chemistry model has been experimentally validated against known spectroscopic techniques, and the fluid model has been experimentally validated against the time-resolved shadowgraphy. The model demonstrates the capability to replicate emergent flow structures near a wall. These structures contribute to momentum transport that enhance the boundary layer’s wall attachment and provide for better flow control.
An experiment was designed to validate the model predictions. The spectroscopic results confirmed the model predictions of an electron temperature of 0.282eV and an electron number density of 65.5 × 10⁻¹²kmol/m³ matching to within a relative error of 12.4% and 14.8%, respectively. The shadowgraphic results also confirmed the model predicted velocities of flow structures of 3.75m/s with a relative error of 10.9%. The distribution of results from both experimental and model velocity calculations strongly overlap each other. This validated model provides new and useful information on the effect of Dielectric Barrier Discharge actuators on flow control and performance. This work was supported in part by NSF grant CNS-0960081 and the HokieSpeed supercomputer at Virginia Tech.Ph. D.
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Lau, Bobby Wing Shun. "A complete model of the infrared dielectric function of a low-density silica aerogel /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
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Kiley, Erin Marie. "Reduced-Dimensional Coupled Electromagnetic, Thermal, and Mechanical Models of Microwave Sintering." Digital WPI, 2016. https://digitalcommons.wpi.edu/etd-dissertations/212.
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In recent years, sintering of powdered materials in microwaves has emerged as a manufacturing technique with many potential advantages over conventional sintering methods, including the possibility of faster processing and finer microstructure, along with the potential for vast energy savings. However, the technique remains on the level of laboratory studies and is underutilized in industry, mostly due to the difficulty of controlling the process: the intrinsically nonuniform temperature pattern that results from microwave heating routinely induces nonuniform mechanical deformation. Mathematical models and computer simulations can help to clarify the factors that influence this process and aid experimentalists in the design of efficient processing equipment. Although a number of modelling techniques have been reported to this end, they appear to inadequately represent the entire chain of related physical phenomena, which involves interaction of the electromagnetic field with the material, heat transfer, and mechanical deformation, each of which is coupled with both of the others, and all of which occur on different time scales. In this work, we present an original comprehensive mathematical formulation that accounts for the chain of physical processes comprising microwave sintering in one- and two-dimensional scenarios. We develop models for simulating the coupled electromagnetic, thermal, and mechanical phenomena at their appropriate time and spatial scales, and in addition, we account for the temperature and density dependence of the full set of thermal and dielectric properties of the material undergoing sintering. The electromagnetic and temperature fields are approximated using finite difference methods, and the mechanical problem is solved using the Master Sintering Curve representation of the density kinetics, which gives a way of accounting for the effect of microscale transport on the macroscopic property of relative density. For constant-rate sintering trials, we use the exponential integral to compute the work of sintering, which reduces computation time. The presented algorithms are all implemented and shown in MATLAB and Python. Simulation of density and temperature evolution of the sintered sample shows processing times and shrinkage rates comparable to experimental results. This work lays a theoretical and computational foundation for modelling the general three-dimensional problem and computer-aided design of efficient sintering processes.
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Sandberg, Lars. "Solubility Modelling in Condensed Matter. Dielectric Continuum Theory and Nonlinear Response." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3351.
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Folgar, Carlos Eduardo. "Structure Evolution of Silica Aerogel under a Microwave Field." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27801.
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Structure evolution of silica aerogel was studied in microwave- and conventionally processed samples over the temperature range from 25 to 1200â °C. The samples were produced using sol-gel processing and dried under carbon dioxide supercritical conditions. After drying, the monolithic samples received a thermal treatment at different programmed temperatures in two different ovens, conventional and microwave. The microwave process was performed using a single mode microwave oven at 2.45GHz. Dielectric properties were measured using the cavity perturbation method, and structural characterization was carried out using a variety of techniques, including absorption surface analysis, Helium pycnometry, Archimedes principle, Fourier transform infrared spectroscopy, X-ray diffraction, and high resolution microscopy. The data obtained revealed that structural differences do exist between microwave- and conventionally processed samples.
Three different regions were identified from the structural characterization of the samples. Regions I exhibited a structure densification at temperatures between 25 and 850â °C. Region II was characterized by a bulk densification in the temperature range from 850 to 1200â °C. Region III was represented by the onset of crystallization above 1200â °C. Explanation and possible causes behind the structural differences observed in each region are provided. In general, the structure evolution observed in microwave- and conventionally processed samples followed the same order, but occurred at lower temperature for the microwave process.Ph. D.
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Sotomayor, Polar Manuel Gustavo. "Analysis of Microstrip Lines on Substrates Composed of Several Dielectric Layers under the Application of the Discrete Mode Matching." Thesis, University of Gävle, University of Gävle, University of Gävle, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-3106.
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Microstrip structures became very attractive with the development of cost-effective dielectric materials. Among several techniques suitable to the analysis of such structures, the discrete mode matching method (DMM) is a full-wave approach that allows a fast solution to Helmholz equation. Combined with a full-wave equivalent circuit, the DMM allows fast and accurate analysis of microstrips lines on multilayered substrates.
The knowledge of properties like dispersion and electromagnetic fields is essential in the implementation of such transmission lines. For this objective a MATLAB computer code was developed based on the discrete mode matching method (DMM) to perform this analysis.
The principal parameter for the analysis is the utilization of different dielectric profiles with the aim of a reduction in the dispersion in comparison with one-layer cylindrical microstrip line, showing a reduction of almost 50%. The analysis also includes current density distribution and electromagnetic fields representation. Finally, the data is compared with Ansoft HFSS to validate the results.
The German Aerospace Center has rights over the thesis work
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Son, Seyul. "Nonlinear Electromechanical Deformation of Isotropic and Anisotropic Electro-Elastic Materials." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28587.
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Electro-active polymers (EAPs) have emerged as a new class of active materials, which produce large deformations in response to an electric stimulus. EAPs have attractive characteristics of being lightweight, inexpensive, stretchable, and flexible. Additionally, EAPs are conformable, and their properties can be tailored to satisfy a broad range of requirements. These advantages have enabled many target applications in actuation and sensing. A general constitutive formulation for isotropic and anisotropic electro-active materials is developed using continuum mechanics framework and invariant theory. Based on the constitutive law, electromechanical stability of the electro-elastic materials is investigated using convexity and polyconvexity conditions. Implementation of the electro-active material model into a commercial finite element software (ABAQUS 6.9.1, PAWTUCKET, RI, USA) is presented. Several boundary and initial value problems are solved to investigate the actuation and sensing response of isotropic and anisotropic dielectric elastomers (DEs) subject to combined mechanical and electrical loads. The numerical response is compared with experimental results to validate the theoretical model.
For the constitutive formulation of the electro-elastic materials, invariants for the coupling between two families of electro-active fibers (or particles) and the applied electric field are introduced. The effect of the orientation of the electro-active fibers and the electric field on the
electromechanical coupling is investigated under equibiaxial extension. Advantage of the constitutive formulation derived in this research is that the electromechanical coupling can be illustrated easily by choosing invariants for the deformation gradient tensor, the electro-active fibers, and the electric field. For the electromechanical stability, it is shown that the stability can be controlled by tuning the material properties and the orientation of the electro-active fibers. The electromechanical stability condition is useful to build a stable free energy function and prevent the instabilities (wrinkling and electric breakdown) for the electro-elastic materials. The invariant-based constitutive formulation for the electro-elastic materials including the isotropic and anisotropic DEs is implemented into a user subroutine (UMAT in ABAQUS: user defined material) by using multiplicative decomposition of the deformation gradient and the applicability of the UMAT is shown by simulating a complicated electromechanical coupling problem in ABAQUS/CAE. Additionally, the static and dynamic sensing and actuation response of tubular DE transducers (silicone and polyacrylate materials) with respect to combined electrical and mechanical stimuli is obtained experimentally. It is shown that the silicone samples have better dynamic and static sensing characteristics than the polyacrylate. The theoretical modeling accords well with the experimental results.Ph. D.
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Arik, Enis. "Dielectric Properties Of Fuel Oils And Their Ethanol Mixtures Investigated By Terahertz Time-domain Spectroscopy." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615463/index.pdf.
Full textAbstract:
The purpose of this study is to investigate the dielectric properties of fuel oils and their ethanol mixtures in the THz spectral region. We presented frequency dependent absorption coefficients, refractive indices, and dielectric constants calculated from the measurements of pure and mixtures of fuel oils. As the mixing ratio changes, meaningful shifts were observed in refractive index and absorption coefficient of the mixtures. For pure liquids, we used Debye model which provides a good estimate for the dielectric parameters of pure liquids in microwave region and also in the THz region. Bruggeman model, which is used for describing the interaction between liquids in binary mixtures, did not work for ethanol mixtures of gasoline within our assumptions. However, these mixtures were modeled successfully with a modified Debye model in which the mixture behavior was described with a basic contribution approach. The results suggest that there is no strong interaction between the ethanol and the molecules in the gasoline. We concluded that this new approach offers a simple and useful method to determine the concentration of ethanol in gasoline with 3% (by volume) maximum error.