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1
Silva, Igor. "Propriétés des matériaux isolants pour application dans les appareillages moyenne tension à tension continue". Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALT043.
Testo completoAbstract (sommario):
Les récentes avancées dans la technologie du courant continu, du côté du transport à haute tension et de la consommation à basse tension, ont propulsé le courant continu de moyenne tension (MVDC) au premier plan. Cette thèse explore les propriétés isolantes en courant continu de deux matériaux couramment utilisés dans l'équipement de distribution : de l'époxy chargé en micro-silice et le silicone elastomère.Dans une configuration monocouche, chaque matériau a fait l'objet d'une enquête approfondie, mettant l'accent sur les caractéristiques de sorption d'eau et la conduction électrique. Des mesures de courant ont été effectuées pour analyser la conduction dans divers niveaux de champs, à différentes températures et conditions d'absorption d'eau. De plus, la méthode Laser Pressure Pulse (LIPP) a été utilisée pour des mesures de charge d'espace en tant que technique complémentaire. L'étude s'est étendue à une configuration bicouche, combinant les deux matériaux, nous permettant ainsi de confirmer un modèle prédisant les propriétés du multicouche et sa distribution de champs en fonction des valeurs des monocouches.La conduction en courant continu dans l'époxy a montré une forte dépendance à l'absorption d'eau, l'humidité influençant la non-linéarité et modifiant le mécanisme de conduction. À l'inverse, le silicone a démontré une conduction limitée par l'électrode, avec des variations de courant liées à la sorption d'eau par le biais d'un mécanisme limité par saturation. Dans une configuration bicouche hypothétique, où l'époxy représente un manchon et le silicone sert de terminaison de câble, le champ est censé se concentrer dans l'époxy dans des environnements secs, passant au silicone à mesure que l'humidité augmente. La thèse se conclut par des discussions sur les stratégies de sélection des matériaux et la conception de configurations multicouchesRecent advancements in direct-current technology from the high-voltage transport and low-voltage consumption have brought medium-voltage DC (MVDC) to the forefront. This thesis delves into the insulating DC properties of two commonly used materials in distribution equipment: epoxy filled with silica and silicone rubber.In a monolayer configuration, each material underwent extensive investigation, focusing on water sorption characteristics and electrical conduction. Current measurements were conducted to analyze conduction under various fields, temperatures, and water uptake conditions. Additionally, the Laser Pressure Pulse (LIPP) method was employed for space charge measurements as a complementary technique. The study extended to a bilayer configuration, combining both materials, with insights from monolayer experiments informing the properties of the bilayer and predicting field distribution.The DC conduction in epoxy exhibited high dependence on water absorption, with moisture influencing non-linearity and altering the conduction mechanism. Conversely, silicone demonstrated electrode-limited conduction, with current variations tied to water sorption through a saturation-limited mechanism. In a hypothetical bilayer configuration, where epoxy represents a type-C bushing and silicone serves as the cable termination, the field is expected to concentrate in the epoxy in dry environments, shifting to silicone as humidity increases. The thesis concludes with discussions on material selection strategies and the design of multi-layer configurations
2
Hu, Chuan. "Study of the thermal properties of low k dielectric thin films /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p9992820.
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3
Duong, Danny. "The complex dielectric properties of aqueous ammonia from 2 GHz - 8.5 GHz in support of the NASA Juno mission". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42891.
Testo completoAbstract (sommario):
A new model for the complex dielectric constant, ε, of aqueous ammonia (NH4OH) has been developed based on laboratory measurements in the frequency range between 2-8.5 GHz for ammonia concentrations of 0-8.5 %NH3/volume and temperatures between 277-297 K. The new model has been validated for temperatures up to 313 K, but may be consistently extrapolated up to 475 K and ammonia concentrations up to 20 %NH3/volume. The model fits 60.26 % of all laboratory measurements within 2σ uncertainty. The new model is identical to the Meissner and Wentz (2004) model of the complex dielectric constant of pure water, but it contains a correction for dissolved ammonia. A description of the experimental setups, uncertainties associated with the laboratory measurements, the model fitting process, the new model, and its application to approximating jovian cloud opacity for NASA's Juno mission to Jupiter are provided.
4
Farnsworth, Kimberly Dawn Richards. "Variable frequency microwave curing of polymer dielectrics". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/10928.
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5
Patel, Kaushal Sharad. "Technique for determining through-plane modulus of thin polymer dielectrics". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/10993.
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6
Moulart, Alexandre Marc. "High dielectric and conductive composites for electromagnetic crystals". Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17092.
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7
Manepalli, Rahul Nagaraj. "Electron beam curing of thin film polymer dielectrics". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11036.
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8
Tear, Gareth Richard. "Shock properties of homogeneous anisotropic dielectrics". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/53828.
Testo completoAbstract (sommario):
Anisotropy, the directional dependence of a physical quantity, is present in numerous physical processes involved in the shock compression of solid materials. The effect that a particular property’s anisotropy has on the propagation of a shock wave is obscured by other effects such as those from strain rate and material heterogeneity. Recent studies have focussed on single- and bi-crystal metals to understand the effect of crystal anisotropy on the mechanics of shock wave propagation. This thesis extends this work to optically transparent non-metallic dielectric single crystals by developing an optical model for anisotropic dielectrics and performing experimental measurements to test the validity of that optical model. Current optical models for shock compressed materials use an isotropic Gladstone- Dale model or isotropic modifications of the Gladstone-Dale model. This thesis extends the isotropic Gladstone-Dale model to an anisotropic photoelastic model for the optical behaviour of linear anisotropic materials under shock compression in the elastic regime. The model uses static photoelastic tensor values available in the literature to predict material response under uniaxial strain in an arbitrary crystal orientation. The effect of varying photoelastic tensor values is studied using Monte Carlo techniques, and confidence intervals on dynamic predictions are presented. Polarimetry is applied to experimentally measure birefringence under shock compression delivered using plate impact on a single stage light gas gun. This method is used to validate the linear photoelastic model developed in this thesis. Experiments were performed on < 10-10 > (a-cut) sapphire up to 15 GPa longitudinal stress and < 10-10 > (a-cut) calcite up to 2 GPa longitudinal stress. It was found that the birefringence of a-cut sapphire under shock compression behaved in agreement with the model in the elastic regime for a 5% error on the photoelastic tensor. Furthermore it was found that birefringence predictions for a-cut calcite as given by the same model did not agree with experimentally measured results. The discrepancy was 0.3% at 1.2 GPa, in excess of 5 standard deviations. Possible reasons for the discrepancy are put forward. Current optical models for shock compressed materials use an isotropic Gladstone-Dale model or isotropic modifications of the Gladstone-Dale model. This thesis extends the isotropic Gladstone-Dale model to an anisotropic photoelastic model for the optical behaviour of linear anisotropic materials under shock compression. The model uses static photoelastic tensor values available in the literature to predict material response under uniaxial strain in an arbitrary crystal orientation. The effect of varying photoelastic tensor values is studied using Monte Carlo techniques, and confidence intervals on dynamic predictions are presented. Polarimetry is applied to experimentally measure birefringence under shock compression. This method is used to validate the linear photoelastic model developed in this thesis. Experiments were performed on ⟨1 0 1 0⟩ (a-cut) sapphire and ⟨1 0 1 0⟩ (a-cut) calcite. It was found that the birefringence of a-cut sapphire under shock compression behaved in agreement with the model. Furthermore it was found that birefringence predictions for a-cut calcite as given by the same model did not agree with experimentally measured results. Possible reasons for the discrepancy are put forward.
9
Boon, Dirk Francois. "The link between daily rainfall and satellite radar backscatter data from the ERS-2 scatterometer in the Free State Province, South Africa". Diss., Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-10272008-132211.
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10
Ben, ghzaiel Tayssir. "Synthèse, caractérisation et étude des propriétés magnétiques et diélectriques de nanocomposites Polyaniline/hexaferrite pour l'absorption des micro-ondes". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN003/document.
Testo completoAbstract (sommario):
Ces travaux de thèse consistent à élaborer des nanocomposites Polyaniline/hexaferrite pour l’absorption des micro-ondes. L’idée principale est la mise en œuvre de matériaux composites à base de polymères conducteurs intrinsèques telle la Polyaniline que nous avons dopée avec différents types d’acides (HCl, CSA, NSA et TSA…) et l’hexaferrite de baryum de type magnétoplombite (M) stœchiométrique ou substitué. Au niveau de l’hexaferrite de baryum, la substitution du Fe3+ s’est faite par les ions Al3+, Bi3+, Cr3+ et Mn3+.L’hexaferrite de baryum et les hexaferrites substitués par les différents ions cités ci-dessus ont été synthétisés par voie hydrothermale dynamique en faisant varier divers paramètres au cours de la synthèse (pH, température, temps, rapport [OH-]/[NO3-]…).L’élaboration des composites Polyaniline/hexaferrite (pur ou substitués) a été effectuée par polymérisation oxydative en utilisant plusieurs techniques de synthèse : la polymérisation chimique en solution (en tenant compte de la nature de l’acide utilisé) avec ou sans agitation (Aqueous-Based Polymerization with or without stirring) et la polymérisation oxydative par voie solide (Solid-Based Polymerization). L’optimisation de ces différentes techniques de synthèse après caractérisations physicochimiques (DRX, FTIR, ATG, MEB, EDX), diélectriques (ε’, ε’’, σdc) et magnétiques (Mr, Ms, Hc, Tc, µ’, µ’’) des échantillons, a montré que la polymérisation par voie solide se trouve la méthode la plus facile, économique et respectueuse de l’environnement. Elle est aussi adaptée à la production du composite Pani/BaFe12O19 avec de bonnes propriétés structurales, physiques et magnétiques. L’étude de la substitution du Fe3+ dans le BaFe12O19 par Al3+, Bi3+, Cr3+ et Mn3+ a montré une forte dépendance des propriétés structurales et magnétiques avec la distribution de ces ions dans la maille cristalline hexagonale. En effet, les ions Al3+, Cr3+ et Mn3+ ont une tendance à occuper les sites tétraédriques, alors que le Bi3+ occupe les sites octaédriques. Une augmentation de Hc associée à la taille des cristallites a été observée pour les particules substituées avec l'Al et le Cr alors qu’une modification de l'anisotropie magnetocristalline (fort terme d'ordre supérieur) a été mise en évidence pour les substitutions Bi et Mn, dû à leur grand rayon ionique. L’incorporation des hexaferrites substitués dans la Polyaniline pour obtenir des composites Pani/BaMeFe11O19, où Me = Al, Bi, Cr et Mn, révèle une variation des propriétés électromagnétiques dans la gamme de fréquences allant de 1 à 18 GHz. En effet, ces variations sont dues à la formation de dipôles entre l’ion de substitution et les cations O2- dans le ferrite qui sont responsables de la résonance ferromagnétique, de l'anisotropie magnétocristalline et des interactions avec la matrice polymérique. Le composite Pani/BaFe12O19 présente des absorptions dans la bande X qui se déplacent vers la bande Ku avec la substitution du fer confirmantThis thesis deals with the formulation of Polyaniline/hexaferrite nanocomposite for absorbing electromagnetic waves. The main idea is the process of composite materials based on polymers intrinsic conductors such as polyaniline that we doped with different types of acids (HCl, CSA, NSA, and ... TSA) and barium hexaferrite with magnetoplumbite structure with or without substitution according to desired stoichiometries. In the barium hexaferrite, the substitution of Fe 3+ is made by Al3+, Bi3+, Cr3+ and Mn3+ ions.The barium hexaferrite and its substitutions by different ions mentioned above were synthesized dynamic hydrothermal method by varying various parameters during the synthesis (pH, temperature, time, ratio [OH-]/[NO3-] ...).The elaboration of polyaniline/hexaferrite composite (pure or substituted) was carried out by oxidative polymerization using various synthesis techniques: Aqueous-Based Polymerisation with or without agitation (taking into account the nature of the acid used) (ABP) and Solid-Based Polymerization (SBP). The optimization of these various synthesis techniques after physicochemical (XRD, FTIR, TGA, SEM, EDX), dielectric (ε ', ε' ', σdc) and magnetic (Mr, Ms, Hc, Tc, µ', µ'') characterizations of the samples showed that the solid route is the easiest method, economical and environmentally friendly. It is also suitable for the production of composite Pani/BaFe12O19 with good structural, physical and magnetic properties.The study of the substitution of Fe 3+ in the BaFe12O19 by Al3+, Bi3+, Cr3+ and Mn3+ showed a strong dependence of the structural and magnetic properties with the distribution of these ions in the hexagonal crystal lattice. In fact, Al3+, Cr3+ and Mn3+ ions tend to occupy the tetrahedral sites, while the Bi3+ favoured the octahedral sites. An increase in Hc associated with the small crystallite size observed for particles substituted with Al and Cr and the enhancement magnetocristalline anisotropy (strong higher order term) for Bi and Mn due to their high ionic radius.The incorporation of the substituted hexaferrite in the polyaniline to obtain Pani/BaMeFe11O19 composite, where Me = Al, Bi, Cr and Mn, reveals a variation in electromagnetic properties in the frequency range from 1 to 18 GHz. In fact, these variations are due to the formation of dipoles between the substituting ion and surrounding O2- cations in the ferrite which are responsible for the ferromagnetic resonance, the magnetocrystalline anisotropy and the exchange interaction with the polymer. The composite Pani/BaFe12O19 shows absorption bands at the X-band that shift to the Ku-band with the substitution of iron, confirming the potential of these materials for microwave applications
11
Paz, Ana Marta. "The dielectric properties of solid biofuels". Doctoral thesis, Mälardalens högskola, Akademin för hållbar samhälls- och teknikutveckling, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-10500.
Testo completoAbstract (sommario):
The use of bioenergy has been increasing due to efforts in fossil fuels replacement. Modern bioenergy technologies aim for high efficiency and low pollution levels, which increases the need for methods for the on-line characterization of biofuels. Dielectric methods have been identified as useful for the sensing of solid biofuels because they allow for rapid, nonhazardous, nondestructive, and bulk determination of material properties. The dielectric properties describe the interaction between the material and the electromagnetic waves. Dielectric properties are intrinsic of the materials and can therefore be used for the development of prediction models that can be applied regardless of the measurement technique. The study of the dielectric properties is also important as it improves the understanding of the dielectric behavior of the materials. This thesis focuses on the dielectric properties of solid biofuels and their use in the characterization of these materials. The work presented includes the development of new methods permitting the determination of the dielectric properties of solid biofuels with large particle size (waveguide method), broadband measurement of the dielectric properties (coaxial-line probe), and the use of a previously developed method for the accurate determination of the dielectric properties (free-space method). The results includes the dielectric properties of solid biofuels and their dependence on parameters such as frequency, moisture, density, and temperature. This thesis also presents semi-theoretical models for the determination of moisture content, which obtained a RMSEP of 4% for moisture contents between 34 and 67%, and an empirical model that resulted in a RMSEC of 0.3% for moisture contents between 4 and 13%. Finally, this thesis includes measurements of the influence of salt content on the dielectric properties and a discussion of its use for estimation of the ash content of solid biofuels.
12
Hawkes, J. J. "Hydration dependent dielectric properties of proteins". Thesis, Bucks New University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383159.
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13
Raj, N. "Dielectric and magnetic properties of superlattices". Thesis, University of Essex, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381931.
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14
Giatti, Brandon. "Optical Properties of Nanostructured Dielectric Coatings". PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1940.
Testo completoAbstract (sommario):
Solar cells have extrinsic losses from a variety of sources which can be minimized by optimization of the design and fabrication processes. Reflection from the front surface is one such loss mechanism and has been managed in the past with the usage of planar antireflection coatings. While effective, these coatings are each limited to a single wavelength of light and do not account for varying incident angles of the incoming light source. Three-dimensional nanostructures have shown the ability to inhibit reflection for differing wavelengths and angles of incidence. Nanocones were modeled and show a broadband, multi-angled reflectance decrease due to an effective grading of the index.
Finite element models were created to simulate incident light on a zinc oxide nanocone textured silicon substrate. Zinc oxide is advantageous for its ease of production, benign nature, and refractive index matching to the air source region and silicon substrate. Reflectance plots were computed as functions of incident angle and wavelength of light and compared with planar and quintic refractive index profile models. The quintic profile model exhibits nearly optimum reflection minimization and is thus used as a benchmark. Physical quantities, including height, width, density, and orientation were varied in order to minimize the reflectance. A quasi-random nanocone unit cell was modeled to better mimic laboratory results. The model was comprised of 10 nanocones with differing structure and simulated a larger substrate by usage of periodic boundary conditions. The simulated reflectance shows approximately a 50 percent decrease when compared with a planar model. When a seed layer is added, simulating a layer of non-textured zinc oxide, on which the nanocones are grown, the reflectance shows a fourfold decrease when compared with planar models. At angles of incidence higher than 75 degrees, the nanocone model outperformed the quintic model.
15
Castro, Armando Josà Neves de. "Estudo das Propriedades DielÃtricas da Matriz CerÃmica FeNbTiO6:(ZnO)x para aplicaÃÃes em Radio-FrequÃncia (RF) e Micro-ondas". Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=11535.
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16
Nealon, Thomas Anthony. "The properties of ferroelectric relaxors". Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329982.
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17
Butcher, Steven John. "Relaxor ferroelectricity in (Pbâ†xBaâ†1â†-â†x)(Mgâ†1â†/â†3Nbâ†2â†/â†3)Oâ†3 ceramics". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329474.
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18
Payton, Gerald C. "An investigation into the dielectric properties of selenium". DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 1987. http://digitalcommons.auctr.edu/dissertations/2840.
Testo completoAbstract (sommario):
The nature of chalcogenides as electrets is virtually an unexplored arena. Electrets now exist in a variety of forms such as the electroelectret, thermal electret, photoelectret, radioelectret and magnetelectrets. An investigation of selenium as a dielectric is employed using the method necessary for the preparation of thermal electrets. The effect of the various parameters such as charging time, charging temperature and sample dimensions are investigated and observed. From these observations a conclusion can be made to the type of preferred orientation taking place in the material; be it dipole orientation, ion transfer or carrier displacement.
19
Hinedi, Mohamad Fahd 1964. "HIGH FREQUENCY DIELECTRIC PROPERTIES OF POLYIMIDES FOR MULTILAYER INTERCONNECT STRUCTURES". Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276497.
Testo completoAbstract (sommario):
One of the most important electrical requirements in high performance electronic systems or high speed integrated circuits, is to process larger numbers of electrical signals at much higher speeds. Signal propagation delay must be minimized in order to maximize signal velocities. Therefore, material with low dielectric constant and low dissipation factor is being sought. In this thesis research measurements of dielectric constant and dissipation factor were performed on commercially available polyimides that are used in multilayer interconnect structures. Capacitor structures with a polyimide dielectric were measured up to a 1GHz frequency and 220°C temperature. Polyimides were concluded to be compatible for use in high performance systems such as multilayer interconnect structures.
20
Rajgadkar, Ajay. "Characterization of Dielectric Films for Electrowetting on Dielectric Systems". Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3607.
Testo completoAbstract (sommario):
Electrowetting is a phenomenon that controls the wettability of liquids on solid
surfaces by the application of electric potential. It is an interesting method to handle tiny
amounts of liquid on solid surfaces. In recent times, researchers have been investigating
this phenomenon and have reported some unexplained behavior and degradation in the
Electrowetting system performance. Electrowetting systems include the presence of
electric field and different materials from metals to dielectrics and electrolytes that create
an environment in which corrosion processes play a very important role. With the small
dimensions of the electrodes, corrosion can cause failure quickly when the dielectric fails.
In this work, commonly used dielectric films such as silicon dioxide and silicon
nitride were deposited using Plasma Enhanced Chemical Vapor Deposition and
characterized on the basis of thickness uniformity, etch rate measurements, Dry current –
voltage measurements and Wet current – voltage measurements. Sputtered silicon
dioxide films were also characterized using the same methods. The correlation between
Dry I – V and Wet I – V measurements was studied and a comparison of dielectric
quality of films based on these measurements is presented. Also, impact of different
liquids on the dielectric quality of films was studied.
21
Hinchcliffe, Claire. "Processing and properties of nanocomposite dielectric films". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437011.
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Lisachuk, G. V., R. V. Kryvobok, Y. M. Pitak, O. Lapuzina, N. A. Kryvobok e N. S. Maystat. "Radio-absorbing materials with adjustable dielectric properties". Thesis, Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/38982.
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Chung, Colin. "Dielectrophoretic investigations of internal cell properties". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10044.
Testo completoAbstract (sommario):
Dielectrophoresis (DEP) is a term which describes the motion of polarisable particles induced by a non-uniform electric field. It has been the subject of research into a variety of fields including nanoassembly, particle filtration and biomedicine. The application of DEP to the latter has gained significant interest in recent years, driven by the development of microfluidic “Lab-on-a-chip” devices designed to perform sophisticated biochemical processes. It provides the ability to characterise and selectively manipulate cells based on their distinct dielectric properties in a manner which is non-invasive and label free, by using electrodes which can be readily integrated with microfluidic channels. Under appropriate conditions a biological cell will experience a DEP force directing it either towards or away from concentrations in the electric field. At a so-called “crossover frequency” the cell is effectively invisible to the field resulting in no DEP force, a response typically observed in the 1 kHz to 1 MHz range. Its value is a function of cell membrane dielectric properties and has been the subject of research directed at devices capable of using it to both characterise and sort cells. The aim of this work was to investigate the behaviour of a higher frequency crossover referred to as fxo2, predicted to occur in the 1 MHz to 1 GHz range. At these frequencies the electric field is expected to penetrate the cell membrane and behave as a function of intracellular dielectric properties. Standard lithography techniques have been used to fabricate electrodes carefully designed to operate at these frequencies. The existence of fxo2 was then confirmed in murine myeloma cells, in good agreement with dielectric models derived from impedance spectroscopy. A temperature dependent decrease in its value was observed with respect to the time that cells were suspended in a DEP solution. This decrease is consistent with previous studies which indicated an efflux of intracellular ions under similar conditions. An analytical derivation of fxo2 demonstrates its direct proportionality to intracellular conductivity. Direct control of the crossover was achieved by using osmotic stress to dilute the intracellular compartment and thereby alter its conductivity. By using a fluorophore which selectively binds to potassium, a strong relationship has been demonstrated between the value of fxo2 and the concentration of intracellular potassium. Measurements of fxo2 for an unfed culture demonstrated a correlation with viability and subtle shifts in its distribution were caused by the early stages of chemically induced apoptosis.
24
Humbert, William R. "A new technique for measuring the elctromagnetic properties of rotationally symmetric materials". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/14941.
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Li, Wensheng. "Dielectric properties and defects structure of lead tungstate crystal". HKBU Institutional Repository, 2000. http://repository.hkbu.edu.hk/etd_ra/222.
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Xu, Jianwen. "Dielectric Nanocomposites for High Performance Embedded Capacitors in Organic Printed Circuit Boards". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11525.
Testo completoAbstract (sommario):
Conventionally discrete passive components like capacitors, resistors, and inductors are surface-mounted on top of the printed circuit boards (PCBs). To match the ever increasing demands of miniaturization, cost reduction, and high performance in microelectronic industry, a promising approach is to integrate passive components into the board during PCB manufacture. Because they are embedded inside multilayer PCBs, such components are called embedded passives.
This work focuses on the materials design, development and processing of polymer-based dielectric nanocomposites for embedded capacitor applications. The methodology of this approach is to combine the advantages of the polymer and the filler to satisfy the electric, dielectric, mechanical, fabrication, and reliability requirements for embedded capacitors. Restrained by poor adhesion and poor thermal stress reliability at high filler loadings, currently polymer-ceramic composites can only achieve a dielectric constant of less than 50. In order to increase the dielectric constant to above 50, effects of high-k polymer matrix, bimodal fillers, and dispersing agent are systematically investigated. Surface functionalization of nanofiller particles and modification of epoxy matrix with a secondary rubberized epoxy to form sea-island structure are proposed to enhance the dielectric constant, adhesion and high-temperature thermal stress reliability of high-k composites. To obtain photodefinable high-k composites, fundamental understanding of the photopolymerization of the novel epoxy-ceramic composite photoresist is addressed. While the properties of high-k composites largely depend on the polymer matrix, the fillers can also drastically affect the material properties. Carbon black- and carbon nanotubes-filled ultrahigh-k polymer composites are investigated as the candidate materials for embedded capacitors. Dielectric composites based on percolation typically show a high dielectric constant, and a high dielectric loss which is not desirable for high frequency applications. To achieve a reproducible low-loss percolative composite, a novel low-cost core-shell particle filled high-k percolative composite is developed. The nanoscale insulating shells allow the electrons in the metallic core to tunnel through it, and thereby the composites exhibit a high dielectric constant as a percolation system; on the other hand, the insulating oxide layer restricts the electron transfer between filler particles, thus leading to a low loss as in a polymer-ceramic system.
27
Miller, Stuart M. "Electrical measurement of sucrose in sugar beet". Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294156.
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Calay, Rajnish Kaur. "Electromagnetic heating processes : analysis and simulations". Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/9846.
Testo completoAbstract (sommario):
Electromagnetic heating (EMH) processes are being increasingly used in
the industrial and domestic sectors, yet they receive relatively little
attention in the thermal engineering domain. Time-temperature
characteristics in EMH are qualitatively different from those in
conventional heating techniques due to the additional parameters (viz
dielectric properties of the material, size and shape of the product
and process frequency). From a unified theory perspective, a
multi-purpose model has been developed in order to obtain the heating
characteristics for an arbitrary processing situation. Theoretical
analyses of various EMH processes in materials of various regular
geometries and a range of physical properties have been undertaken.
Despite the wide spread usage of microwave energy in the food
engineering sector. few understand microwaves and their interactions
with foods. Much of the published research is largely focussed from the
view point of an electrical engineer and aimed at the oven designer.
However, trial-and-error methods are usually employed when developing
microwavable food products and when using microwave ovens. The
presented thesis is focussed from the view-point of the thermal
engineer and aimed primarily at food developers and end users.
The multi-purpose model was then modified specifically for simulating
the heating of food materials in a microwave oven. The validity of the
commonly made assumptions was investigated; in particular the variation
of dielectriC properties during the heating processes and their likely
influence on the model's predictions. Experimental data available in
the literature were compiled and analysed to form a set of equations
for predicting the dielectric properties of various food materials.
Also available correlations for thermal properties were evaluated for a
selected set of experimental data of different food materials. Analyses
were undertaken to demonstrate and evaluate the effects of various
parameters on the heating characteristics of different food materials
commonly heated/cooked in microwave ovens. A qualitative comparison of model predictions and experimental measurements is provided to validate
the physical basis of the model. Findings from the model lead to a
better understanding of the interactions between foods and microwaves. [...cont.]
29
Al, Kabsh Asma. "Optical properties and energy applications of MoS2". OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1636.
Testo completoAbstract (sommario):
Transition metal Dichalcogenide MoS2in the monolayer and few-layer form have generated intense interest in the fundamental and applied research community due to its surprisingly strong light-matter interactions, strong excitonic effect, and unique elec-tronic and chemical activity at the edges. In this thesis work, I have conducted a series of synergistic experimental and computational investigations focused on understanding the fundamental optical properties of few-layer MoS2(experiment with supporting computational calculations) and its potential application into the electrochemical reduction of CO2(computational)In the first part of the thesis, I show that sulfur vacancies affect the optical properties of few-layer thin films deposited using magnetron sputtering. In particular, I show that sulfur vacancies can obscure the well-defined A/B excitons in MoS2. Next, while contributing with the process of developing high-quality MoS2films, I designed an approach to accurately determine the optical constants by combining transmission spectroscopy with spectroscopic ellipsometry. The method, which we call Transmission-assisted spectroscopic ellipsometry (TASE), is demonstrated on high-quality MoS2films deposited on transparent and absorbing substrates. Next, Transmission spectroscopy combined with the Kramers-Kronig consistent optical model was employed to determine the complex dielectric function of few-layer MoS2in the broadband energy range of 0.7-6.5 eV. Optical transitions leading to peaks in the dielectric functions are assigned to the band structure. In particular, a new peak is observed and assigned at 4.5 eV in few-layer MoS2. Finally, I have examined the effectiveness of doped MoS2on the catalytic activity for CO reduction using density functional theory method. The structural calculation shows that doping Mo edge site of MoS2with transition metals that have higher work function than Mo atom results a lowering in the CO adsorption energy which suppresses the dissociation reaction and enhances the hydrogenation reaction. The Bader charge analysis shows that the dopant atom does not contribute to CO adsorption directly but it reduces the charge density at the edge atom that is indicated from the Density of states.
30
Al-Dhhan, Z. T. "Dielectric properties of thin films based on CeO2̲". Thesis, Brunel University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380605.
Testo completo
31
Tseng, Jung-Kai. "Enhanced Dielectric Properties of Multilayer Capacitor Film via Interfacial Polarization". Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1449137228.
Testo completo
32
Hasegawa, Keisuke. "The effect of geometry and surface morphology on the optical properties of metal-dielectric systems /". Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2008. http://hdl.handle.net/1794/8581.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of Oregon, 2008.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 127-133). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.
33
Dutta, Saikat Swapan. "Water absorption and dielectric properties of Epoxy insulation". Thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9723.
Testo completoAbstract (sommario):
Characterization of Epoxy (diglycidyl ether of Bis-phenol A cured with Tri ethylene Tetra amine) without fillers was done. The Water absorption test at 95°C shows that at saturation the epoxy contains a water concentration of 2.089%. The diffusion coefficient of absorption is calculated as 0.021 cm2/s. The diffusion coefficient of desorption is calculated as 0.0987 cm2/s. The diffusion is almost 5 times faster than absorption. Also the material looses weight as the hydrothermal aging progresses. The water in the sample leads to chain scission which leads to the weight loss. The weight loss is more incase of absorption followed by desorption than only absorption. The chain scission leads to decrease in the mechanical strength by around 45%. The diffusion of water from the samples doesnt affect the mechanical strength of the materials. The glass transition temperature reduces by 20°C with water inside the sample. The diffusion of water out of the sample only increases by around 10°C. The Dielectric response of the material shows that after the water absorption the sample shows high losses at lower frequencies. Also the increase in the real part of the permittivity increases with low frequency. The rapid increase in the real art of the permittivity of the material at lower frequencies can be attributed to a polarization at the electrode due both to accumulation of the charge carriers and to chain migrations. The breakdown test of the samples shows that with water in the sample the breakdown strength of the material decreases by 10 KV, but the material regains its dielectric strength when the water is diffused out. This shows that the chain scission and weight loss of the samples has no or minimum effect on the dielectric strength of the sample
34
Mallinson, Phillip Martin. "Perovskite Microwave Dielectric Ceramics: Structure, Properties and Processing". Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490899.
Testo completoAbstract (sommario):
Perovskite Microwave Dielectric Ceralnics: Structure, Properties and Processing PhD thesis, Phillip M. Mallinson, University of Liverpool This thesis describes the synthesis and characterisation of several new hexagonal perovskite materials and the investigation into the processing of a commercial microwave dielectric. Chapter 1 is in two parts, the first gives an introduction to the perovskite and hexagonal perovskite structural types, and reviews the structure and properties of reported hexagonal perovskites with the AnBn-\03n general formula. The second part reviews the literature on the microwave dielectric material Ba3ZnTa209 (BZT). In Chapter 2 the details of the synthetic and analytical techniques employed are described. Chapter 3 describes the synthesis and characterisation of a number of new hexagonal perovskite materials. The eight layer compounds BagCoNb60 24 and BagCoTa6024 were found to crystallise with different structures in the space groups P 3ml and P63c11l respectively. A detailed structural description and comparison of the structures of the materials is given along with the dielectric and magnetic properties. The structure and dielectric properties of the six layer material Ba6Ca1l3Nb\4/30\g are also presented. Chapter 4 describes the synthesis and characterisation of two isostructural ten layer hexagonal perovskites with the formulas BalOMgo.25Ta7.903o and BaIOCoO.25Ta7.903o. Refinement of combined synchrotron X-ray and neutron powder diffraction data is used to determine the structures of the materials. The dielectric properties of the materials are reported and the links between dielectric loss and ordering and microstructure discussed. In Chapter 5 the results of an in-situ X-ray powder diffraction study of the ordering and domain growth ofBZT at temperatures between 1200 and 1500 °C is presented. The degree of ordering is quantified using two different methods and a rate of ordering calculated at each of the temperatures studied, from the rates of ordering the activation energy for cation transport is calculated. The ordered domain size is also quantified from the diffraction data and the dynamics compared to domain growth in other systems. Supplied by The British Library - 'The world's knowledge'
35
Ieta, Adrian C. "Charge transfer & dielectric properties in hydrocarbon mixtures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ39835.pdf.
Testo completo
36
Stevenson, Paul John. "High field dielectric properties of hard PZT ceramics". Thesis, University of Manchester, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556653.
Testo completoAbstract (sommario):
At the present time there is an increasing demand for higher acoustic and electric power densities in piezoelectric transducers. The preferred material for such acoustic sources is hard (acceptor doped) lead zirconate titanate (PZT) ceramic due to a combination of desirable properties including high piezoelectric coupling factors, high ~, low electrical losses and good temperature stability. Four commercially available materials from two independent suppliers have been characterised; PZ26 and PZ28, obtained from Ferroperm Ltd, and PC4 and PC8 obtained from Morgan Matroc. The use of Mn as the acceptor dopant was found for the F erroperm materials, and Fe for the Morgan Matroc materials. A finer grain size was also observed in the Morgan Matroc materials by comparison with those from Ferroperm. Various dielectric properties of each material were investigated as a function of field amplitude, ageing time after poling and with regard to the effect of grain size and temperature. A 'threshold field' type of behaviour was observed for all materials followed by a linear increase in permittivity with field level. Such behaviour is related to the Rayleigh law, first introduced to model the behaviour of ferromagnetic materials. The most encouraging results were observed for the Morgan Matroc material with the PC8 exhibiting the most stable performance under high drive conditions. Linear plots of the real versus imaginary parts of the dielectric permittivity were observed for all materials as a function of field amplitude or ageing time an related to a ferroelectric domain wall translation mechanism. The corresponding values of tan Odw, the loss associated with domain wall translation were compared. Evidence was also found for intrinsic and reversible domain wall vibration contributions to the permittivity in the 'low field' region, while partial domain switching was observed on approaching the coercive field Ee. Field-driven de-ageing studies of poled and unpoled PZ26 ceramICS revealed a gradual reduction in the effective internal bias field Ei with time. For poled materials the reduction followed a logarithmic time law, whereas for unpoled materials an exponential decrease was observed.
37
Farsari, Maria. "Dielectric and optical properties of organic photorefractive materials". Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5226/.
Testo completoAbstract (sommario):
The work presented in this thesis is derived from experimentation in the field of polymeric photorefractive materials. Low T(_g) polymeric composites were prepared, based on the well-known photoconductive polymer PVK (maximum 50% w/w), sensitized with TNF (2% w/w) and C(_60) (0.2% w/w), plasticized with ECZ (maximum 49.3% w/w) and doped with the nonlinear optical materials NPP (50% w/w), DAN (20% w/w), DED (5% w/w), DCNQI (0.5% w/w), ULTRA-DEMI (5% w/w) and DI-DEMI (2% w/w), and their dielectric, linear and non linear optical properties were investigated. All the materials, except DCNQI, exhibited good solubility and sample processibility. The dielectric properties of the composites at 1 KHz and 1 MHz were determined using a parallel-plate capacitance bridge. The dielectric constant and loss at 10 GHz were measured using a novel adaptation of the resonant cavity technique, which was designed for measurements at ambient and elevated temperatures. The method was used to measure of the dielectric constant and loss of two novel, high T(_g), electro-optic polymers at temperatures up to 100 ºC. The dielectric properties measured were typical of polymeric materials. The absorption coefficient and the refractive index at different wavelengths were measured using a spectrophotometer. For the refractive index, an interference fringe analysis was used. The nonlinear measurements consisted of second harmonic generation, to prove the nonhnearity of the composites, two-beam coupling measurements, to prove their photorefractivity and degenerate four-wave mixing to measure their diffraction efficiency. The NPP, DAN, DED and ULTRA-DEMI doped investigated composites exhibited second order nonlinearity with highest the one of ULTRA-DEMI, at 292 pm/V for 19 kV of corona poling field. The photorefractivity of the NPP, DAN and DED doped composites was proven at 632.8 nm, while ULTRA-DEMI doped composites photooxidized before any measurements were possible. The two-beam coupling coefficients measured were lower than 20 cm(^-3), while net gain was observed only in the NPP doped composite. The diffraction efficiencies of the NPP, DAN and DED doped composites were measured at 632.8 nm, and were found to be l0(^-5)-l0(^-6).
38
Kenmuir, S. V. J. "Dielectric properties of some oxide and oxynitride glasses". Thesis, Durham University, 1986. http://etheses.dur.ac.uk/7083/.
Testo completoAbstract (sommario):
The main part of this thesis describes dielectric studies on a series of oxynitride glasses prepared at Wolfson Centre for High Strength Materials, University of Newcastle upon Tyne. Bridge techniques were used to determine the room temperature values of permittivity (ε') and dielectric loss (ε") for some Y-Al-Si and Nd-Al-Si oxynitride glasses and for further compositions in the Mg-Al-Sl and Ca-Al-Si systems. Over the range 500 Hz to 10 KHz the frequency dependencies of ε' and conductivity (σ) were found to be in good agreement with the Universal law of dielectric response i.e. (ε'- ε (_∞)) oc ω((^n-1) and σ (ω) oc ω(^n) giving n = 1.0 ± 0.1 for all compositions examined. In all four systems the addition of nitrogen increased the permittivity while, at each concentration of nitrogen (including the oxide glasses) the permittivity increased with cation type in the order magnesium, yttrium, calcium, neodymlum. As regards the higher frequency regime coaxial line techniques were used to determine, at room temperature, both ε' and ε" for some Mg-Al-Si, Ca-Al-Si and Y-Al-Si oxynitride glasses over the frequency range 500 MHz to 5 GHz. Here the frequency dependencies of ε' and ε" are also consistent with the Universal Law of dielectric response in that (ε'- ε(_∞)) oc ω((^n-1)) and ε" oc ω((^n-1)) for all glass compositions. The high experimental value of the exponent (n = 1.0 ± 0.1) suggested the limiting form of lattice loss situation. In this frequency range (as also at the lower frequencies) the addition of nitrogen increased the permittivity and it was confirmed that in both the oxide and oxynitride glasses ε' is influenced by the cation, being increased with cation type in the order magnesium, yttrium, calcium as at lower frequencies. At still higher frequencies, in the microwave region, special cavity perturbation methods of measurement were developed and used. Preliminary studies are also reported on the temperature dependencies of ε' and ε" for a similar range of glass compositions and on the optical behaviour of the oxynitride glasses both in the visible and infra-red regions of the spectrum. In the Appendices summaries are given of published papers on oxynitride glasses (Appendix I) and also on single crystal MgO, Fe/MgO, Cr/MgO and Co/MgO (Appendix II) a study which formed an addendum to the main work.
39
Waters, Cecilia Anne. "Optical, spectroscopic and dielectric properties of metal nanoparticles". Thesis, University of Liverpool, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433996.
Testo completo
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Groenewald, Nico Albert. "Measuring the dielectric properties of crushed copper ore". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5230.
Testo completoAbstract (sommario):
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Previous work has shown that microwave heating of mineral ores induces micro cracks within the ore structure, which can be attributed to the difference in the adsorption of microwaves amongst the different mineral phases. This reduces the energy required during subsequent grinding and enhances the liberation of valuable minerals. In order to design microwave applicators for this purpose, knowledge of the effective dielectric properties of the crushed ore is required. Of particular interest is the effective complex permittivity of the bulk crushed ore. The measurement of the effective permittivity of a large volume of crushed ore is most readily accomplished using the waveguide measurement technique. In this method a representative sample of the material is placed in a defined and fixed volume in a standard size rectangular section metallic waveguide. The magnitude and phase angle of the transmitted and reflected low power microwaves through and from the sample are measured. The complex permittivity can be extracted from these so-called scattering, or Sij parameters. In this study the effective complex permittivities for two porphyry copper ores and a copper carbonatite ore were determined as a function of particle size distribution (-26.5+2mm) using two sizes of waveguide (WR284 and WR340). The sample holders incorporate dielectric windows for the location of the material under test. The extraction of dielectric properties from Sij parameter measurements is problematic using standard algorithms in such cases. Accordingly a new Database Extraction (DBE) Algorithm has been developed. In this method, a database of scattering parameters is established through electromagnetic modelling of the measurement system. A search algorithm is used to determine the effective complex permittivity of the modelled load whose scattering parameters provide the best fit to the experimental data. The goodness of the experimental fit of the simulated to the measured Sij parameters is determined by a root mean squared deviation minimisation metric. Results show that the method can be used successfully to determine an effective complex permittivity for a bulk volume of the crushed material. It is concluded that the dielectric property extraction over the full operational frequency interval (2.3-3 GHz) is preferred as it has a larger degree of extraction confidence and hence reliability. Results show that with increasing particle size, the experimental fit between the simulated and measured Sij parameters becomes increasingly poor, as wall effect become more prominent. The effect is most prominent for the smaller WR284 waveguide size. It is shown that for a waveguide size of similar size to the particle size, the Sij parameter fitting is poorer compared to when a larger waveguide size is used. The extracted complex permittivity reproducibility between repeated dielectric property measurements is improved for the WR340 waveguide size, as the extractions in the WR284 waveguide is dominated by the combined particle size and wall-effects of the sample holder. Ore mineralogy is identified as a key parameter that influences the dielectric properties of the crushed ore. For ores with a dominant microwave absorbent mineral phase, the dielectric constant and loss factor is found to be larger, compared with ores with a more dominant microwave transparent gangue mineral phase.
AFRIKAANSE OPSOMMING: Navorsing toon dat die verhitting van mineraal erts, met mikrogolwe, mikroskaal frakture in die mineraalstruktuur teweeg bring weens die verskil in die adsorpsie van mikrogolwe in die verskillende mineraalfases. Gevolglik verminder die energievereiste vir die vergruising van die erts en verbeter die vrystelling van waardevolle minerale wat vasgevang is in die mineraalmatriks. Vir die ontwerp van mikrogolfapplikators vir dié doel, word die effektiewe diëlektriese eienskappe van die vergruisde erts benodig. Van spesifieke belang is die effektiewe komplekse permittiwiteit van die erts. Die effektiewe permittiwiteit van `n vergruisde materiaal monster word met behulp van die golfgeleier tegniek gemeet. Vir dié tegniek word `n verteenwoordigende monster van die materiaal in `n rigiede volume in `n standaard grootte reghoekige golfgeleier geplaas. Die grootte en fasehoek komponente van die deurgelate en weerkaatste mikrogolwe deur en van die oppervlak van die materiaal word gemeet. Die komplekse permittiwiteit van die vergruisde materiaal kan geëkstrakteer word vanaf hierdie sogenaamde verspreide, of Sij parameters. In hierdie studie word die effektiewe permitiwiteit van twee porforie koper ertse en `n koper karbonatiet erts bepaal as funksie van partikel grootte (-26.5+2 mm) deur gebruik te maak van twee standaard grootte golfgeleiers. Die monster houers inkorporeer diëlektriese vensters om die vergruisde materiaal monster in posisie te hou. In so `n geval is die ekstraksie van die diëlektriese eienskappe vanuit die Sij parameter metings problematies. Gevolglik is ‘n nuwe Databasis Ekstraksie Algoritme ontwikkel wat `n databasis van verspreide parameters opstel deur die elektromagnetiese simulasie van die metingsisteem. `n Soek-algoritme word gebruik om die effektiewe komplekse permitiwiteit van die gesimuleerde monster te bepaal wat die beste ooreenstem met dié van die gemete eksperimentele Sij parameter data. Die mate van ooreenstemming tussen die parameters, word bepaal aan die hand van die minimaliserings prosedure. Resultate toon dat dié metode geskik is vir die bepaling van die effektiewe komplekse permitiwiteit van die vergruisde monster. Dit word vasgestel dat die betroubaarheid van die geëkstraeerde Sij parameters, en gevolglik die diëlektriese eienskappe van die erts, toeneem indien die algoritme oor `n groter frekwensie band uitgevoer word. Resultate toon verder dat met toenemende partikel grootte, die mate waartoe die absolute grootte en fasehoek komponente van die gesimuleerde en gemete Sij parameters ooreenstem, versleg. Dit word toegeskryf aan wand-effekte. Hierdie verskynsel is veral opmerklik vir die kleiner grootte golfgeleier. Dit word getoon dat vir metings waar die golfgeleier dieselfde orde grootte geometriese afmetings het as die vergruisde erts self, die passing tussen die gesimuleerde en gemete Sij parameters swakker is, wanneer dit vergelyk word met metings waar dit nie die geval is nie. Die reproduseerbaarheid van die geëkstraeerde diëlektriese eienskap waardes verbeter vir lesings wat uitgevoer word in `n groter grootte golfgeleier. Laasgenoemde word toegeskryf aan die meer dominante wand-effekte wat kenmerklik is vir `n kleiner golfgeleier. Erts mineralogie word geïdentifiseer as `n sleutel parameter wat die diëlektriese eienskappe van die vergruisde materiaal beïnvloed. Beide die diëlektriese konstante en verliesfaktor is groter vir ertse met `n oorheersende mikrogolf absorberende mineraalfase.
41
Ayoob, Raed. "Dielectric properties of hexagonal boron nitride polymer nanocomposites". Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/417272/.
Testo completoAbstract (sommario):
There is a growing research interest in polymer nanocomposite materials due to their potential in enhancing dielectric properties. However, a considerable amount of variability exists in the literature regarding the electrical performance of polymer nanocomposites, and therefore the underlying mechanisms underpinning their electrical properties are still far from fully understood. Possible reasons for the existing inconsistencies could be due to different material preparation techniques, different nanoparticle dispersion states, unknown filler content, inconsistent sample storage conditions, and unknown water level content in the samples. Determining the principal factors that dominate the electrical behaviour of polymer nanocomposites could allow engineers to tailor the electrical properties of dielectrics for their specific application. As a result, the work reported in this thesis was mainly set out to explore the factors governing the electrical properties of polymer nanocomposites such that the inconsistencies in the literature can be better understood, and consequently eliminated. This thesis investigated the performance of hexagonal boron nitride (hBN) nanocomposites based on two thermoplastic polymers: polystyrene and polyethylene. Prior to producing any nanocomposites, the hBN particles were characterised using different techniques. The characterisation primarily revealed that the boron nitride particles are in the hexagonal form and the surface of hBN contains a scarce amount of hydroxyl groups. Polystyrene nanocomposites were prepared containing identical amounts of hBN dispersed in different solvents in an attempt to obtain different dispersion states, as a result of different hBN/solvent interactions. The effect of solvent processing was negligible on the dispersion state of the hBN in the polystyrene; no observable difference in the dispersion and electrical properties was reported although the presence of hBN resulted in a slight increase in the breakdown strength relative to the unfilled polystyrene. A range of polyethylene nanocomposites were produced containing different amounts of hBN to understand the effect of the dispersion or aggregation state of the hBN on the breakdown strength. The results revealed that the nanocomposites, regardless of the morphology, exhibited a monotonic increase in breakdown strength with increasing hBN content from 2 wt % to 30 wt %, while maintaining the low dielectric losses of the unfilled polyethylene. While the hBN was found to have a strong nucleating effect on the polyethylene, it was determined that the local change in morphology was not the cause of the enhanced breakdown strength as both the polyethylene nanocomposites obtained by rapid crystallisation, where the development of spherulites was suppressed, and the amorphous polystyrene nanocomposites, also exhibited an improved breakdown strength. Further experiments indicated that the polyethylene nanocomposites did not absorb any moisture from the environment in ambient conditions, and absorbed a very small amount of water even in the 30 wt % polyethylene/hBN nanocomposite when completely immersed in water. Dielectric spectroscopy measurements revealed that the surface hydroxyl groups on the hBN are most likely located only on the edge surfaces of the hBN rather than basal surfaces. The water was most likely loosely bound to the hBN particles, where local water clusters formed. It was remarkable that a percolating water network was not formed in a nanocomposite consisting of an already percolating hBN network, which was largely attributed to the surface chemistry of hBN. Despite the presence of water in the system, the hBN nanocomposites continued to exhibit an enhanced breakdown strength in comparison to the unfilled polyethylene. Therefore, this thesis demonstrated that the electrical behaviour of polymer nanocomposites is most likely dominated by the surface state of the nanoparticles and how the particles interact with the charge carriers; any other effects due to local morphological changes or nanoparticle dispersion are considered to be secondary reasons for changes in the electrical properties.
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Liu, Huijin. "The elastic and dielectric properties of structural ceramics". Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285312.
Testo completo
43
Abbas, Zulkifly. "Determination of the dielectric properties of materials at microwave frequencies using rectangular dielectric waveguide". Thesis, University of Leeds, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569541.
Testo completo
44
Borthakur, Swarnal Ho P. S. "The effects of post-ash cleaning and chemical treatments on the dielectric properties and reliability of Cu/low-k interconnect structures". 2005. http://repositories.lib.utexas.edu/bitstream/handle/2152/1826/borthakurs44073.pdf.
Testo completo
45
Borthakur, Swarnal. "The effects of post-ash cleaning and chemical treatments on the dielectric properties and reliability of Cu/low-k interconnect structures". Thesis, 2005. http://hdl.handle.net/2152/1826.
Testo completo
46
Jayanthi, S. "Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications". Thesis, 2006. https://etd.iisc.ac.in/handle/2005/392.
Testo completoAbstract (sommario):
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by the A/B cationic ratio. The role of transition metals of the 3d series from vanadium (Z=23) to zinc (Z=30) in modifying the crystallographic phase content, microstructure and the dielectric properties of BaTiO3 ceramics containing 10 at% impurities were studied. All the transition metals brought about the phase conversion to hexagonal BaTiO3, although no systematics could be arrived at relating the hexagonal content to the 3d electronic configuration of the impurities. The relaxor dielectrics arising from the titanate solid solution with uncommon substitution and its interconversion to normal ferroelectrics is studied. The effects of cationic substitutions of iron and niobium for titanium in BaTiO3 pervoskite lattice in crystal symmetry and dielectric properties were investigated. The above dielectric characteristics are comparable in a converse way to those of the well known Pb(Mg1/3Nb2/3)O3-PbTiO3 system wherein the relaxor behaviour occurs within the lower lead titanate compositional limits. The modification in -T characteristics of positive temperature coefficient in resistance (PTCR) by the addition of segregative additives such as B2O3, Al2O3 etc in BaTiO3 and its conversion to grain boundary layer capacitance is studied. The presence of Al-related hole centers at the grain boundary regions resulted in charge redistribution across the modified phase transition temperatures due to symmetry-related vibronic interactions, which result in broad PTCR characteristics extending to higher temperatures. The processing of high permittivity ceramics by the manipulation of microstructural features in semiconducting BaTiO3 is studied wherein the grain boundary layer effect superimposed with the contributions from the barrier layers formed during electroding related to microstructure is proposed to be responsible for the unusual high permittivity in semiconducting BaTiO3. The influence of Mg2+ as a substituent in modifying the crystallographic phase contents, microstructure and the dielectric properties of (Ba1-xMgx)TiO3 ceramics, (x ranging from zero to 1.0 ) is studied. The results point to the dual occupancy of Mg2+ both in A and B sublattice and the role of oxygen vacancy as well as (Ti3+ –VO) defects in stabilization of hexagonal phase to lower temperatures. The microwave dielectrics of the BaMg6Ti6O19 phase formed in the compositional range of x=0.4 to 0.7 was investigated for suitable application in microwave dielectrics. Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ and La3+. The resulting Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The elemental distribution reveals the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. Microwave dielectric property of Mg4Al2Ti9O25 which is detected as secondary phase is studied in detail.
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Jayanthi, S. "Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications". Thesis, 2006. http://hdl.handle.net/2005/392.
Testo completoAbstract (sommario):
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by the A/B cationic ratio. The role of transition metals of the 3d series from vanadium (Z=23) to zinc (Z=30) in modifying the crystallographic phase content, microstructure and the dielectric properties of BaTiO3 ceramics containing 10 at% impurities were studied. All the transition metals brought about the phase conversion to hexagonal BaTiO3, although no systematics could be arrived at relating the hexagonal content to the 3d electronic configuration of the impurities. The relaxor dielectrics arising from the titanate solid solution with uncommon substitution and its interconversion to normal ferroelectrics is studied. The effects of cationic substitutions of iron and niobium for titanium in BaTiO3 pervoskite lattice in crystal symmetry and dielectric properties were investigated. The above dielectric characteristics are comparable in a converse way to those of the well known Pb(Mg1/3Nb2/3)O3-PbTiO3 system wherein the relaxor behaviour occurs within the lower lead titanate compositional limits. The modification in -T characteristics of positive temperature coefficient in resistance (PTCR) by the addition of segregative additives such as B2O3, Al2O3 etc in BaTiO3 and its conversion to grain boundary layer capacitance is studied. The presence of Al-related hole centers at the grain boundary regions resulted in charge redistribution across the modified phase transition temperatures due to symmetry-related vibronic interactions, which result in broad PTCR characteristics extending to higher temperatures. The processing of high permittivity ceramics by the manipulation of microstructural features in semiconducting BaTiO3 is studied wherein the grain boundary layer effect superimposed with the contributions from the barrier layers formed during electroding related to microstructure is proposed to be responsible for the unusual high permittivity in semiconducting BaTiO3. The influence of Mg2+ as a substituent in modifying the crystallographic phase contents, microstructure and the dielectric properties of (Ba1-xMgx)TiO3 ceramics, (x ranging from zero to 1.0 ) is studied. The results point to the dual occupancy of Mg2+ both in A and B sublattice and the role of oxygen vacancy as well as (Ti3+ –VO) defects in stabilization of hexagonal phase to lower temperatures. The microwave dielectrics of the BaMg6Ti6O19 phase formed in the compositional range of x=0.4 to 0.7 was investigated for suitable application in microwave dielectrics. Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ and La3+. The resulting Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The elemental distribution reveals the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. Microwave dielectric property of Mg4Al2Ti9O25 which is detected as secondary phase is studied in detail.
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Sheu, Jeng-Dong, e 許正東. "A Study of the Properties of Plasma-Deposited Fluorine-Doped SiO2 for Low Dielectric Constant Interlevel Dielectrics". Thesis, 1996. http://ndltd.ncl.edu.tw/handle/18848492960420935220.
Testo completoAbstract (sommario):
碩士國立交通大學
電子研究所
84
We have studied the properties of fluorine-doped silicon dioxide (SiOF)deposited by adding CF4 to conventional tetraethylorthosilicate(TEOS)-basedplasma-enhanced chemical vapor deposition (PECVD). Dielectric constants of SiOF films are reduced from 3.8 to 3.2 by the addition of CF4. Si-F bond formation in the films is detected by chemical bonding structural studies using Fourier Transform Infrared Spectroscopy (FTIR). Low dielectric constants are caused by Si-F bond formation. The reduction of the dielectric constant apparently results from a decrease of the ionic polarization. As thefluorine content increases, the SiOF films becomes more unstable to moistureabsorption. The moisture absorption of SiOF with high fluorine content are caused by the porosity and formation of Si-F2 in the films. The thermal stability of SiOF films is investigated by rapid thermal annealing (RTA). The fluorine contents of SiOF films decrease with increasing RTA temperature.However, the dielectric constants of the SiOF films remain the same up to 600C under low moisture absorption condition. Atomic force microscopic(AFM)pictures reveal the densification and the reduction in surface roughness ofSiOF films after RTA treatments. In order to stabilize dielectric constants of SiOF films which increase with the increase of moisture absorption, a surface oxynitridation is required. We find that N2O-plasma annealing in an effective way to block moisture. The dielectric constants of SiOF films treated by the N2O-plasma annealing rarely change.
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"Studies on thermal stabilities of transparent dielectrics/ZnO heterostructures". 2007. http://library.cuhk.edu.hk/record=b5893211.
Testo completoAbstract (sommario):
Wang, Ranshi = 透明电解质/氧化锌异质结热稳定性的研究 / 王然石.Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.
Includes bibliographical references (leaves 130-134).
Abstracts in English and Chinese.
Wang, Ranshi = Tou ming dian jie zhi/yang hua xin yi zhi jie re wen ding xing de yan jiu / Wang Ranshi.
Chapter I. --- Abstract
Chapter II. --- Acknowledgement
Chapter III. --- Table of contents
Chapter IV. --- List of figures
Chapter V. --- List of tables
Chapter 1 --- Introduction
Chapter 1.1 --- Motivations
Chapter 1.2 --- Outline of thesis
Chapter 2 --- Experimental Conditions and Techniques Used
Chapter 2.1 --- Sample preparation
Chapter 2.1.1 --- Radio frequency magnetic sputtering
Chapter 2.1.2 --- ITO glass
Chapter 2.1.3 --- Thermal evaporation
Chapter 2.1.4 --- Thermal annealing
Chapter 2.2 --- Optical characterization of ZnO
Chapter 2.2.1 --- Photoluminescence (PL) measurement
Chapter 2.2.2 --- SEM and cathodoluminescence spectroscopy
Chapter 2.3 --- Time-of-FIight Secondary Ion Mass Spectroscopy (TOF-SIMS )
Chapter 2.4 --- Electrical measurements
Chapter 3 --- Calibrations
Chapter 3.1 --- Sample Thickness
Chapter 3.2 --- Calibrations of cathodeluminescence measurements
Chapter 3.2.1 --- Probe current and specimen current
Chapter 3.2.2 --- Sample uniformity in CL measurement
Chapter 3.2.3 --- Mirror position
Chapter 3.2.4 --- Non-linear relation between CL emission and current
Chapter 3.2.5 --- CL band-edge emission stability
Chapter 3.2.6 --- Effect of magnification
Chapter 3.2.7 --- Effect of electron beam shift
Chapter 3.2.8 --- Conclusions
Chapter 3.3 --- C-V measurement
Chapter 4 --- Experimental Results and Data Analysis
Chapter 4.1 --- Optical properties
Chapter 4.1.1 --- Luminescence of ZnO
Chapter 4.1.2 --- Light emitting thermal stability of A10x (MgO) capped ZnO film
Chapter 4.1.2.1 --- Emission degradations in annealing treatment by PL
Chapter 4.1.2.2 --- Evidence about the interface degradation
Chapter 4.1.2.3 --- CL studies of the emission from sample surface
Chapter 4.2 --- Secondary Ion Mass Spectroscopy (SIMS) studies of AIOx-capped ZnO
Chapter 4.2.1 --- Data processing
Chapter 4.2.2 --- Diffusion width
Chapter 4.3 --- Simulation of Zn out diffusion to the dielectric layer
Chapter 4.3.1 --- Structure and assumptions
Chapter 4.3.2 --- Calculations of diffusion by Fick's Law
Chapter 4.3.3 --- Simulation of PL reduction from diffusion
Chapter 4.3.4 --- Short-time PL
Chapter 4.4 --- Simulation of defects generation in emission reduction process
Chapter 4.4.1 --- Some calculations of continuity equation
Chapter 4.4.2 --- First order equation for defect generation
Chapter 4.5 --- Electrical measurements
Chapter 4.5.1 --- Theory of C-V measurement for MOS structure
Chapter 4.5.1.1 --- MOS Structure
Chapter 4.5.1.2 --- Discussions about surface charge and energy level in C-V experiments of MOS
Chapter 4.5.1.3 --- Useful formulations
Chapter 4.5.2 --- Experimental results of C-V and parameter extraction
Chapter 4.5.2.1 --- Effect of series resistance correction
Chapter 4.5.2.2 --- Effect of thermal annealing to C-V curves on dielectric/ZnO/ITO
Chapter 4.5.2.3 --- Doping concentration (ND)
Chapter 4.5.2.4 --- Discussion about the fixed and mobile charge
Chapter 4.5.3 --- Simulation of C-V relation in dielectric/ZnO
Chapter 4.5.4 --- Current-voltage (I-V) measurements
Chapter 4.5.5 --- Conductance-voltage measurements (G-V) and interface trap density
Chapter 4.5.6 --- DLTS measurements for extracting interface trap density
Chapter 5 --- Discussions and Conclusion
Chapter 5.1 --- Mechanism
Chapter 5.2 --- Conclusions
Chapter 5.3 --- Future plan
Chapter 6 --- References
50
"Dielectric microspheres as optical cavities". Chinese University of Hong Kong, 1988. http://library.cuhk.edu.hk/record=b5885964.
Testo completo