The objective of this thesis is to develop a complex dielectric properties sensor using interdigitated capacitor (IDC) structure. IDCs are easy to fabricate and because of its planar structure, it can be easily integrated with other sensing components and signal processing electronics. The design, fabrication, modeling, and testing of IDC sensors are presented in this thesis. Design parameters and their influence on sensor's output signals are discussed. Previous IDC models are reviewed and the limitations are studied. A new equivalent circuit model based on the fringing electric field distribution and a novel iterative data extraction algorithm combining Finite-Element Method (FEM) and the equivalent circuit model is studied. Results suggest that the algorithm can accurately extract relatively low dielectric constant and conductivity of material under test (MUT) from measured impedance data. / text

New VLSI and VHSIC devices require increased performance from electronic packages. The major challenge that must be met in materials/process development for high complexity and high speed integrated circuits is the processing of even larger amounts of signals with low propagation delay. Hence, materials with low dielectric constant and low dissipation factor are being sought. In this investigation the dielectric properties of the most commonly used composite materials for printed circuit boards, Teflon-glass and Epoxy-glass, were measured in the frequency and temperature intervals of 100 HZ-1 GHZ and 25-260°C, respectively. From the measured results, it is concluded that Teflon-glass is more suitable for the board level packaging of high performance circuits due to its lower dielectric constant and low dissipation factor.

This thesis studies two important carbon structures, graphene and carbon nanotubes, with the purpose of understanding how their three-dimensional electron density distribution affects the way fast ions interact with them. <br /><br /> A brief introduction to research in pure carbon structures is made. We then use different models to calculate the equilibrium electron density distribution in graphene and carbon nanotubes. <br /><br /> In the second part of the thesis we investigate fast ions moving parallel to a graphene sheet and experiencing forces due to the dynamic polarization of carbon valence electrons. Using the three-dimensional electron density distribution of graphene, we calculate the force directly opposing the ion's motion (stopping force), as well as the force which bends the ion's trajectory towards the sheet (image force). It is our purpose to compare these results with those based on a two-dimensional hydrodynamic model of graphene, which approximates the electron distribution of graphene by a charged fluid confined to the two-dimensional plane of the sheet. <br /><br /> The results obtained for interactions of ions with a single graphene sheet should be useful for a further analysis of ion channeling through carbon nanostructures.

Approved for public release; distribution is unlimited / A general study of conductor backed coplanar waveguide is presented. The impedance (Z(0)) and effective dielectric constant (ɛ(reff)) of conductor-backed coplanar waveguide (CBCPW) have been calculated by using a variational method and the boundary point matching method. In this present work only the TEM dominant low frequency propagation mode of coplanar line has been considered. Experimental facilities are vector network analyzer (HP8409) and bench-instrument measurements. / http://archive.org/details/evaluationofcopl00jeon / Captain, Korean Air Force

Master of Science / Food Science Institute / Karen A. Schmidt / Radio frequency dielectric heating (RFDH) can provide rapid and uniform heating throughout the products' mass, and can be used to bake, dry, and defrost foods. Studies have shown that when RFDH induced a 5-log reduction of Salmonella spp. in nonfat dry milk (NDM), whey protein nitrogen index (WPNI) decreased, suggesting that functional properties of the NDM might be impacted. This research was conducted to determine if RFDH affected the functional properties of NDM [high-heat (HH) and low-heat (LH)]. Nonfat dry milk were treated to 75, 80 and 85°C in the RFDH unit, then were held for 125, 63 and 43 min for LH-NDM or 115, 52 and 43 min for HH-NDM, and cooled to ~23 ± 1°C. Powders were evaluated for WPNI , nitrogen solubility index, and color. Maillard browning and functional properties of NDM samples were evaluated after NDM was rehydrated to 3.5% protein with deionized water, and adjusted to pH 7.00. Glucono-delta-lactone was added in rehydrated NDM (3.5% protein; natural pH) as an acidifying agent to form milk gels, and the physical properties of the gels were determined. Two replications were conducted and data were analyzed with two-way ANOVA (RFDH and NDM) and Tukey mean differentiations (p ≤ 0.05). Results showed that LH-NDM (collapsed for RFDH treatments) had 5.7% less viscosity, 20.9% less overrun, 27.4% less foam stability, as well as 15% less water holding capacity compared with HH-NDM (collapsed for RFDH treatments). This can be explained by the natural whey protein denaturation differences in the HH-NDM and LH-NDM. Viscosity and surface tension were impacted by the RFDH treatment. NDM (HH and LH) treated to 85°C had 10% greater viscosity than the control, and the NDM treated to 75°C had less surface tension compared with samples treated to 80°C, 85°C and the control. Overall, RFDH decreased WPNI in LH-NDM, but not HH-NDM. The SDS-PAGE gel images provided supportive evidence to the WPNI results. RFDH is a processing technology that could change a few functional properties of NDM in this study, which makes it a promising method that may be further exploited for various food applications, such as emulsifiers, foaming agents, etc. However, potential negative impacts, such as color change caused by Maillard reaction, loss of WPNI in LH-NDM, cannot be neglected.

<p>Nature is challenged to move charge efficiently over many length scales. From sub-nm to μm distances, electron-transfer proteins orchestrate energy conversion, storage, and release both inside and outside the cell. Uncovering the detailed mechanisms of biological electron-transfer reactions, which are often coupled to bond-breaking and bond-making events, is essential to designing durable, artificial energy conversion systems that mimic the specificity and efficiency of their natural counterparts. Here, we use theoretical modeling of long-distance charge hopping (Chapter 3), synthetic donor-bridge-acceptor molecules (Chapters 4, 5, and 6), and de novo protein design (Chapters 5 and 6) to investigate general principles that govern light-driven and electrochemically driven electron-transfer reactions in biology. We show that fast, μm-distance charge hopping along bacterial nanowires requires closely packed charge carriers with low reorganization energies (Chapter 3); singlet excited-state electronic polarization of supermolecular electron donors can attenuate intersystem crossing yields to lower-energy, oppositely polarized, donor triplet states (Chapter 4); the effective static dielectric constant of a small (~100 residue) de novo designed 4-helical protein bundle can change upon phototriggering an electron transfer event in the protein interior, providing a means to slow the charge-recombination reaction (Chapter 5); and a tightly-packed de novo designed 4-helix protein bundle can drastically alter charge-transfer driving forces of photo-induced amino acid radical formation in the bundle interior, effectively turning off a light-driven oxidation reaction that occurs in organic solvent (Chapter 6). This work leverages unique insights gleaned from proteins designed from scratch that bind synthetic donor-bridge-acceptor molecules that can also be studied in organic solvents, opening new avenues of exploration into the factors critical for protein control of charge flow in biology.</p> / Dissertation

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017 / This research has considered an idealistic non-interleaved planar transformer wherein only the electromagnetic parasitic capacitive and inductive elements arising out of the transformer geometry are taken into account, without considering material limitations. A suitable model for the planar transformer is used to analyse its frequency and power transfer characteristics; this model was validated by three dimensional electromagnetic simulations of various planar transformer structures in FEKO simulation software. The capacitive and inductive parasitics in this model have been found to be functions of the dielectric thickness. The theoretical bandwidth for the planar transformer is defined in this research as a function of dielectric thickness. The effect of dielectric thickness of the transformer windings on the bandwidth of the transformer is analysed, based on the premise that the inherent parasitic capacitive and inductive elements would affect the transfer characteristics of the transformer. Upon conclusion of this analysis, it is found that the dielectric thickness of a planar transformer can be optimised such as to present an optimised bandwidth. A closed form analytic expression for the optimum dielectric thickness value is derived and presented in this research. In a design example of a 4:1 50W transformer presented in this research, it has been shown that the bandwidth can be improved by 384%, along with a power density improvement of 45%, upon choosing of an optimum dielectric thickness of 0.156mm to replace a standard 0.4mm thick dielectric. It should be noted that the results derived in this research are purely theoretical, justified by many idealisations and assumptions that are argued throughout the research. It is thus expected that practical results should at best approach the theoretical results, due to the known non-ideal nature of reality. / CK2018

Ionômeros são polímeros carregados que possuem uma variedade de propriedades elétricas e que recentemente vêm sendo aplicados como camadas de transporte em dispositivos poliméricos. Em particular, camadas ultrafinas de ionômeros são depositadas entre o eletrodo e o polímero eletrônico em OLEDs para aumentar a eficiência da injeção de cargas. Entretanto o sucesso desta aplicação envolve fenômenos de armazenamento e mecanismos de transportes de cargas dentro do ionômero que ainda não são claramente entendidos. Neste trabalho foi utilizada a técnica da corrente despolarização termoestimulada (TSDC) com o propósito de esclarecer alguns efeitos relacionados a esse fenômeno. Nós utilizamos o poliestireno sulfonado (X-SPS) com lítio (X = Li) ou potássio (X = K) como contraíon. Foram obtidos filmes ultrafinos com 50 nm de espessura por spincoating obtendo a estrutura metal-polímero-metal para estudo, tendo como metal o alumínio. A técnica de TSDC consiste no aquecimento de uma amostra previamente polarizada a um taxa de aquecimento constante e a corrente de despolarização é medida em função da temperatura da amostra. Os resultados experimentais mostraram que cada termograma apresenta dois picos, sendo que um dos deles mostrou-se fortemente dependente das condições de polarização, ou seja, dependendo da temperatura de polarização e da intensidade do campo de polarização. Os picos foram estudados através da cinética de primeira ordem para a dinâmica de armazenamento e transporte, e dos ajustes teórico-experimental foram obtidos importantes parâmetros, tal como, a energia de ativação e concentração de espécies ativas. / Ionomers are charged polymers that exhibit a great variety of electrical properties and more recently they have been applied as transport layers at polymer devices. In particular, thin films of ionomer have been deposited between the electrodes and the electronic polymers in OLEDs to improve the efficiency of the charge injection. Despite the success of such application, the involved phenomena related to the charge storage and transport mechanisms inside the ionomer thin layer are not clear yet. In this work we used thermal stimulated depolarization current technique (TSDC) with the purpose to elucidate such phenomena. We used for this a sulfonated polystyrene (X-SPS) having lithium (X = Li) or potassium (X = K) as cation counter-ions, and we make structure of metal-polymer-metal in which the polymer is a thin film of SPS, at about 50 nm thick and deposited by spincoating, having aluminum as metal. TSDC technique consists of warm up a previously polarized sample at a constant rate of heating and measure the depolarization current in function of the temperature. The experimental results showed that each thermogram presents two peaks, one of them very dependent on the polarization conditions, i. e., it depends on the polarization temperature and the intensity of the polarization bias. The peaks were studied by considering first order trapping-detrapping (or dipole relaxation) kinetics, from which important parameters, as the activation energy, were obtained.

Realizamos medidas dielétricas a baixas freqüências (10-2-40Hz) em cristais de KCN empregando uma ponte de ultra-baixas freqüências, bem como a altas freqüências (50-104 Hz) empregando uma ponte de capacitância comercial (General Radio). As curvas de perda dielétrica mostraram um bom ajuste entre altas e baixas freqüências. Obtivemos picos de perda dielétrica num intervalo de cinco décadas e entre 53 e 78K. Os picos destas curvas foram ajustados segundo uma equação de Arrhenius, e obtivemos uma energia de ativação de 0,148 eV e um tempo de relaxação característico de 6,53 x 10-15s para os dipolos CN-. Para temperaturas entre 53 e 59K observamos o aparecimento gradual de um segundo pico de perdas de 25Hz. Sua origem ainda não é conhecida, mas isto sugere que o cristal de KCN pode apresentar propriedades de um dielétrico composto, com dois mecanismos de relaxação distintos. / Dielectric measurements were performed at low frequencies (10-2- 40Hz) with an ultra-low frequency bridge in KCN crystals , as well as at high frequencies (50-10-4 Hz) employing a commercial capacitance bridge (General Radio). The dielectric loss curves show a good adjustment between the high and low frequencies. We obtain dielectric loss peaks in a window of five decades and in the range of 53 and 78 K. The peaks of these curves were fitted with an Arrhenius expression giving for the CN- dipoles an activation energy of 0,148eV and an attempt relaxation time of 6,53x10-15. At temperatures between 53 and 59K we observed the gradual appearing of a second loss peak for frequency of 25Hz. Its origin is not yet known butt his suggestt that the KCN, crystal may present compound dielectric properties , with - two distinct relaxation mechanisms.

Estudos do comportamento dielétrico, viscoelástico e fisico-químico, em função do tempo de envelhecimento, foram realizados no polietileno reticulado (XLPE). Neste trabalho, utilizaram-se amostras comerciais de cabos isolados, envelhecidas em condições definidas no laboratório e amostras envelhecidas em campo durante 25 anos. As amostras foram cortadas com aproximadamente 150 ?m de espessura, desde a camada mais externa até a camada mais interna do polietileno. A espectroscopia dielétrica foi realizada no intervalo de 10 ?Hz a 1 MHz e mostra a presença de picos de relaxação, obedecendo as formas assintóticas da função susceptibilidade de Dissado-Hill. Com o envelhecimento em laboratório a temperatura ambiente (RT) e campo, a região mais externa mostra processo de condução quase permanente, dominando com o envelhecimento. Por outro lado, com o envelhecimento em temperaturas superiores, observou-se um processo tipo perda plana (\"flat-loss\") de relaxação dipolar dominando em regiões mais internas. O comportamento viscoelástico foi investigado, através de análise dinâmico-mecânica, e indica que um envelhecimento de natureza eletroquímica gera diferentes processos como: quebra de cadeias, variações na cristalinidade e reticulação, com o envelhecimento. Além disso, estes resultados foram confrontados com outros resultados, obtidos através de técnicas adicionais, como: espectroscopia de infravermelho por transformada de Fourier, difratometria de raios-X, grau de reticulação, microscopias ópticas e de varredura eletrônica. / Dielectric, viscoelastic and physical-chemical studies have been performed in cross- Linked polyethylene (XLPE) as a function of the aging time. This work was carried out in insulation cables field aged for twenty five years and XLPE cables laboratory aged under multi-stressing conditions. The samples, field and laboratory aged, were peeled with approximately 150 ?m thickness, at the surface just below the outer layer just above the inner layer. The dielectric spectroscopy, carried out in the frequency range 1 ?Hz to 1 MHz, show the presence of relaxation peaks obeying the asymptotic foms of Dissado and Hill susceptibility functions. For the aged samples, obtained from the outer layer position, conduction near pemanent process with aging time was observed. On the other hand, at middle and inner layer positions, was observed a Flat-loss process, which becomes dominant with aging time. In addition, viscoelastic properties have also been investigated through dynamic mechanical analysis, suggesting that eletrochemical aging effects generates different processes involving: chains breakage, changes cristallinity and cross-linking with aging time. Furthermore, the previous results have been confronted with other results obtained with additional techniques such as: Fourier transform infrared spectroscopy, X-rays measurements, cross-link degree, optical and scanning electronic microscopies.