In order to improve efficiency and reliability of the world's power grids, sensors are being deployed for constant status monitoring. Placing inexpensive wireless sensors on high-voltage power lines presents a new challenge to the RF engineer. Large electric field intensities can exist around a wireless sensor antenna on a high-voltage power line, leading to the formation of a corona plasma. A corona plasma is a partially ionized volume of air formed through energetic electron-molecule collisions mediated by a strong electric field. This corona can contain large densities of free electrons which act as a conducting medium, absorbing RF energy and detuning the sensor's antenna. Through the use of low-profile antennas and rounded geometries, the possibility for corona formation on the antenna surface is greatly reduced, as compared with wire antennas. This study looks at the effects of a corona plasma on a patch antenna, which could be used in a power line sensor. The corona's behavior in the presence of an electromagnetic plane wave is analyzed mathematically to understand the dependence of attenuation on frequency and electron density. A Drude model is used to convert plasma parameters such as electron density and collision frequency to a complex permittivity that can be incorporated in antenna simulations. Using CST Microwave Studio, a 5.8 GHz patch antenna is simulated with a plasma material on its surface, of varying densities and thicknesses. Power absorption by the plasma dominates the power loss, as opposed to detuning. A wideband patch is simulated to show that the detuning effects by the plasma can be further reduced. Power absorption by the plasma is significant for electron densities greater than 10¹⁸ m⁻³. However, small point corona are found to have little effect on antenna radiation.

Made available in DSpace on 2014-06-11T19:23:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-30Bitstream added on 2014-06-13T20:50:25Z : No. of bitstreams: 1 gianelli_bf_me_bauru.pdf: 728578 bytes, checksum: 08bd745e090c422288e1a15f08401cdf (MD5) / O acúmulo de sais na superfície de isoladores acarreta a formação de arcos sobre os mesmos, aumentando o processo de corrosão por ácido nítrico. Essa corrosão pode iniciar uma falha da cadeia de isoladores. Atualmente o principal método para análise da corrosão em isoladores, baseia-se em câmaras térmicas e não se tem mostrado adequado para a detecção de defeitos por poluição salínica em seus estágios iniciais. Esse projeto propõe, a adoção de câmeras corona que operam em um comprimento de onda variando entre 240 - 280 nm, filtrando totalmente os raios solares UVA e UVB e permitindo a detecção do ponto aonde se encontra presente a anomalia. Embora as câmeras corona tenham sido amplamente utilizadas, principalmente em linhas de 135 kV até 500 kV, poucos experimentos foram realizados com as mesmas em tensões de 69 kV, tensão padrão da empresa patrocinadora do projeto. Nossa proposta é a de apresentar uma nova metodologia de inspeção utilizando esses equipamentos e possibilitando à empresa incrementar as suas atividades de inspeção. / The accumulation of salt on the surface of insulators causes the formation of arcs, increasing the corrosion process by nitric acid. This corrosion can start a fault of the insulators chain. Presently the main method for corrosion analysis of insulators is based on thermal cameras and is not adequated to detect defects caused by salt pollution on initial stages. This project proposes the adoption of corona cameras operating in wavelengths ranging from 240 to 280 nm, with filters to block UVA and UVB from sunrays and allowing the detection of anomalous spots. Although the corona cameras have been widely used, especially in lines of 135 kV to 500 kV, few experiments have been performed with such an instrument at 69 kV, that is the standard voltage of the company sponsoring of the project. Our proposal is to present a new methodology for inspection using such instrument that enables the company to improve its inspection activities.

The solar corona is a highly conductive plasma which is dominated by the coronal magnetic field. Observations show that important solar phenomena like flares or the heating of the corona are driven by magnetic energy, probably through the process of magnetic reconnection. The release of magnetic energy by reconnection requires that non-ideal processes take place in contradiction to the high conductivity of the corona. One possibility to overcome this problem is to generate strong electrical currents in strongly localised regions. In this thesis we investigate how such localised currents can be formed by slow ideal evolution of topologically simple magnetic fields. To this purpose numerical simulations are carried out using an Eulerian and a Lagrangian MHD relaxation code. We first use a simple example (twisting of a uniform field) to investigate the advantages and disadvantages of both codes and to discover possible limitations for their application. We show that for the problems addressed in this thesis the Lagrangian code is more suited because it can resolve the localised current densities much better than the Eulerian code. We then focus in particular on magnetic fields containing a so-called Hyperbolic Flux Tube (HPT). A recently proposed analytical theory predicts that HFT's are sites where under certain conditions strong current build-up can be expected. We use our code to carry out a systematic parametric study of the dependence of current growth for a typical HFT configuration. We have also developed a completely new version of the analytical theory which is directly based on the set-up of our numerical simulations. We find that the simulations agree with the analytical prediction in a quantitative way but that the analytical theory underestimates the current growth quite substantially, probably by not taking into account the non-linear character of the full problem.

Electrohydrodynamics (EHD) is a promising research field with several trending applications. Even though the phenomenon was first observed centuries ago, there is very little research until the middle 20th century, as the mechanisms behind it were very poorly understood. To this date, the majority of research is based on the development of empirical models and the presentation of laboratory experiments. This work begins with an extensive literature review on the phenomenon, clarifying conflicts between researchers throughout the history and listing the findings of the latest research. The literature review reveals that there are very few mathematical models describing even the most important parameters of the EHD fluid flow and most are either empirical or greatly simplified. As such, practical mathematical models for the assessment of all primary performance characteristics describing EHD fluid accelerators (Voltage Potential, Electric Field Intensity, Corona Discharge Current and Fluid Velocity) were developed and are begin presented in this work. These cover all configurations where the emitter faces a plane or another identical electrode and has a cylindrical surface. For configurations where the emitter faces a plane or another identical electrode and has a spherical surface, Corona Discharge Current and Fluid Velocity models have been presented as well. Laboratory experiments and computer simulations were performed and are being thoroughly presented in Chapter 4, verifying the accuracy and usability of the developed mathematical models. The laboratory experiments were performed using two of the most popular EHD electrode configurations - wire-plane and needle-grid. Finally, the findings of this research are being summarized in the conclusion, alongside with suggestions for future research. The step-by-step development of the equipotential lines mathematical model is presented in Appendix A. Appendix B covers the mathematical proof that the proposed field lines model is accurate and that the arcs are perpendicular to the surface of the electrodes and to all of the equipotential lines.

Although the solar corona is one of the most studied areas in solar physics, its activity, such as flares, prominence eruptions and CMEs, is far from understood. Since the solar corona is a low-ß plasma, its structure and dynamics are driven by the magnetic field. The aim of this PhD thesis to study the magnetic field in the solar corona. Unfortunately, high quality direct measurements of the coronal magnetic field are not available and theoretical extrapolation using the observed photospheric magnetic field is required. The thesis is mainly divided in two parts. The first part deals with the comparison between theoretical models of magnetic fields and observed structures in the corona. For any theoretical model, a quantitative method to fit magnetic field lines to observed coronal loops is introduced. This method provides a quantity C that measures how closely a theoretical model can reproduce the observed coronal structures. Using linear force-free field extrapolation, the above field line fitting method is used to study the evolution of an active region. The method is also illustrated when the theoretical magnetic field depends on more than one parameter. The second part of the thesis focuses on the linear force-free field assumption using two different geometric configurations. Firstly a vertical rigid magnetic flux tube is considered. The analytical expression of the magnetic field is obtained as an expansion in terms of Bessel functions. The main properties of this system are discussed and compared with two cylindrically symmetric twist profiles. For the second system, the photosphere is assumed to be an infinite plane. Using translational geometry, the analytical expression of the linear force-free magnetic field that matches a prescribed line of sight magnetic field component is obtained. This solution is compared with the non-linear solution obtained by Roumeliotis (1993).

Foram construídas duas montagens experimentais: Com a primeira, mediu-se o decaimento do potencial de superfície em circuito aberto, em função da temperatura; com a segunda mediu-se diretamente a corrente termo-estimulada (derivada do potencial de superfície em circuito aberto) aquecendo-se a amostra a uma taxa constante. Usando essas técnicas estudamos as propriedades de transporte e armazenamento de cargas no Teflon FEP-A, carregado com corona. Usando a segunda técnica, verificou-se que amostras descarregadas, do citado material, podem liberar portadores de cargas positivas que dão origem a uma corrente anômala, que pode interferir nas medidas de corrente termo-estimulada de amostras carregadas positivamente. Estudou-se o comportamento das curvas de corrente em amostras com e sem tratamento térmico, carregadas com corona tanto positiva como negativa. Além disto, é feita uma discussão dos resultados por nós obtidos e os publicados na literatura. / Two experimental systems were constructed: with the first the surface potential could be measured, while with the second, its derivative with respect to the time (the so called open circuit current). In both cases the measurements were performed while heating previously positive or negative corona charged FEP-A Teflon 25&#956m samples. The results gave information about charge storage and transport properties in this material. During the work it was noticed that positive ions maybe emitted from Teflon surface. This unexpected phenomenon was followed in some detail in order to know how far it influences the usual currents. This study led us to carry measurements in previously annealed samples, whose behavior was found to differ from that of virgin samples. Our results were compared with those found in the literature.

A técnica do triodo de corona com corrente constante foi utilizada para carregar amostras de PVDF na fase &#945, acompanhando a evolução do potencial de superfície durante o carregamento. Com essa técnica foi possível não só obter a fase &#945p a partir da fase &#945 como também analisar o comportamento elétrico de ambas as fases. Os resultados obtidos em ambiente úmido mostram que a forma geral das curvas de potencial nas amostras carregadas com corona positiva e negativa são similares, ou seja, no início do carregamento tem-se um salto inicial, continua crescendo numa taxa mais lenta até alcançar um valor máximo de potencial e a partir deste valor decai para um regime estacionário. Os valores de potenciais alcançados na superfície da amostra não foram suficientes para gerar campos elétricos da ordem 1.5MV/cm, requeridos para induzir uma transição para a fase &#945p. Apesar de ocorrerem mudanças no comportamento elétrico durante os carregamentos, nenhuma mudança na estrutura das amostras foi detectada, usando a técnica de difratometria de raios-X. Em ambiente seco foi verificado que, durante o carregamento, o potencial na superfície da amostra alcançava valores altos quando comparado aos obtidos em ambiente úmido. Verificou-se também, que as amostras apresentavam enrugamento, característicos de materiais poliméricos. As mudanças ocorridas devido ao carregamento foram detectadas pela técnica de raios-X, confirmando a mudança de estrutura para &#945p. O comportamento ferroelétrico das amostras na fase &#945p, foi identificado pela curva de evolução do potencial de superfície, onde se avalia a quantidade de polarização ferroelétrica adquirida. As mudanças de estrutura e das propriedades elétricas em ambiente seco foram irreversíveis. / The constant current corona triode was used for charging &#945-PVDF samples and monitoring their surface potential buildup during poling. It is shown that the method allows one to obtain the polar &#945p form of PVDF from the non-polar &#945-form and also to analuse electrical characteristics of both forms. The experimental results obtained with samples under humid conditions show a similar behavior for positive and negative corona. There is na initial steep increase in the surface potential which then increases passing through a maximum value, and decreases until a steady state is reached. The maximum values attained are not sufficiently high to attain electric fields of around 1.5MV/cm required for causing a phase change from &#945 to &#945p. Furthermore, no change in the structure of the samples is noted in X-ray diffractograms. For measurments carried out under dry conditions, on the other hand, the sample surface potential attain much higher values. The samples become wrinkled after being submitted to these high electric fields (&#62 1.5MV/cm), and this is characteristic of ferroelectric materials. The change to &#945p from samples is confirmed by the structural changes exhibited in X-ray diffractograms. The ferroelectric behavior of the &#945p samples is further identified by the surface potential buildup, from which the remanent polarization can be inferred. The structural as well as the electric changes caused by the corona charging are found to be irreversible.

Neste trabalho foi investigado o comportamento elétrico dos sistemas poliméricos preparados com o poliestireno, PS, e poli(metacri1ato de metila), PMMA, dopados com o corante vermelho disperso 1, DR1. O processo de polarização dos filmes poliméricos foi realizado usando o triodo de corona operando em duas configurações: i) carregamento com corrente de carga constante, ii) com tensão de grade constante. O processo de polarização por corona foi investigado variando-se os parâmetros do processo, tais como: corrente de carga, tempo, temperatura, campo elétrico de saturação e porcentagem de corante das amostras. As medidas da corrente elétrica no estado estacionário em função campo elétrico permitiram mostrar que o processo de condução elétrica nos dois sistemas obedecem o modelo de Poole-Frenkel. O valor da polarização elétrica induzida foi avaliada através de medidas do coeficiente piroelétrico, o qual é diretamente proporcional a polarização na amostra. No caso do PS(DR1) deu-se ênfase a investigação de medidas de corrente termo estimulada para avaliar a polarização elétrica induzida nas amostras por aplicação de uma ddp. Medidas da constante dielétrica complexa para os dois sistemas poliméricos foram realizadas em função da freqüência para diferentes temperaturas. Os resultados obtidos mostraram que a orientação e relaxação dos corantes nas amostras são associados ao movimento das cadeias poliméricas, i.e., relaxação do tipo &#945. / Some electrical properties of guest-host polymeric systems made with polystyrene, PS, and poly(methyl methacrylate), PMMA, and the disperse red 1 dye, DR1 were investigated. The poling process of films were performed with the corona triode set up operating in two modes: i) charging with constant current, ii) with a constant grid voltage. The influence of parameters such as the charging current, electric field at the s, time, temperature and the percentage of DR1 was investigated. Measurements of the steady state current versus the electric field allowed us to show that the electric conduction process in both polymeric systems follow the Poole-Frenkel model. The electric polarization induced in samples was evaluated measuring the piroelectric coefficient, which is directly proportional to the polarization value. For PS(DR1) samples thermally stimulated current measurements were performed to investigate the electric polarization obtained by application of a dc voltage. Measurements of the complex dielectric constant with the two polymeric systems as function of the frequency for different temperatures were performed. Results showed that orientation and relaxation of DR1 dye in samples are related to the chain movement, i.e., &#945 relaxation process.

Orientador: João Sinézio de Carvalho Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T16:49:59Z (GMT). No. of bitstreams: 1 Sena_HildoCostade_M.pdf: 22003439 bytes, checksum: 1eca2b2806567e926cea6f94abd18776 (MD5) Previous issue date: 2011 / Resumo: Este trabalho avalia o efeito do tratamento por descarga corona em temperatura ambiente e acima para promover aumento da energia de superfície em filmes de polipropileno (PP). Submeteram-se amostras de polipropileno ao tratamento corona em sistema com geometria ponta-plano e utilizou-se de tensão de polarização dos eletrodos em 5kV . Avaliaram-se os efeitos do tratamento corona através de medidas de ângulo de contato pelo método da gota séssil, em função dos parâmetros: tempo de tratamento corona (2s a 90s), temperatura das amostras de polipropileno (25_C e 55_C) e distância entre os eletrodos (3mm e 5mm). Os resultados indicam influência significativa do tempo de tratamento corona e da distância intereletrodos. Ademais, o tratamento corona aumenta a energia de superfície dos filmes observada através da diminuição do valor do ângulo de contato entre amostra e gota d'água (inicialmente 88_ sem tratamento e 50_ após corona com 3mm de distância entre os eletrodos). Dentre os parâmetros e condições estudadas a temperatura não apresenta influência nos valores de ângulo de contato a fim de mudar a energia de superfície dos filmes. Em adição as medidas de ângulo de contato, medem-se propriedades físico-químicas da superfície do PP através da obtenção dos espectros dos filmes por espectrometria de infravermelho com transformações de Fourier (FT-IR) e de micrografias obtidas por microscopia eletrônica exploratória (MEV). A energia de superfície (antes e após tratamento corona) foi determinada utilizando-se os seguintes métodos: tensão superficial crítica (c), equação de estado (EE) e as aproximações de Owens/ Wendt (OW), Wu (Wu) e van Oss/ Chaudhury/ Good (VCG). A partir destes métodos encontra-se que: foram observadas diferenças entre os espectros de FT-IR obtidos nas diferentes condições de tratamento estudadas quando associadas a modificação por corona sob temperatura acima da ambiente (55_C _ 2_C). Alterações na topografia dos filmes de PP foram observadas após tratamento por descarga corona através da formação de grânulos, depressões, eriçamento e protuberâncias na superfície destes. Melhorias na energia livre superficial dos filmes de PP foram observadas após tratamento corona e variou aproximadamente de 36,9mN=m para 47,9mN=m em filmes sem tratamento superficial e após 10s de tratamento por descarga corona quando determinada através da aproximação de VCG, respectivamente / Abstract: The present study evaluates the effect of corona discharge treatment at room temperature and above in order to promote an increase of surface energy of polypropylene films. Polypropylene samples were subjected to corona treatment in tip-plane geometry system using bias voltage of 5kV between the electrodes. The effects of corona treatment were assessed by contact angle measurements using the sessile drop method, taking in account the following parameters: corona treatment time (2s to 90s), temperature of polypropylene samples (25_C and 55_C) and distance between the electrodes (3mm and 5mm). The results indicate significant influence of treatment time and the distance between the electrodes. Moreover, the corona treatment increases the surface energy of the films which was observed by decreasing the value of the contact angle between thesample and drop of water (initially 88_ without treatment and 50_ after corona with 3mm gap between the electrodes). Among the parameters and conditions studied, the temperature does not influence the values of contact angle in order to change the surface energy of the films. In addition the measures of contact angle, were carried out measures of physicochemical properties of the PP surface by obtaining the spectra of the films by infrared spectrometry with Fourier transformed (FT-IR) and micrographs obtained by scanning electron microscopy (SEM). The surface energy (before and after corona treatment) was determined using the following methods: critical surface tension (c), equation of state (EE) and approaches from Owens/ Wendt (OW), Wu (Wu) and van Oss/ Chaudhury/ Good (VCG). From these methods is turning out that: there were differences between the spectra obtained at different FT-IR treatment conditions studied when associate the corona modification at above room temperature (55_C _ 2_C). Changes in the topography of the films PP were observed after treatment by corona discharge due to formation of granules, depressions, bristling and bumps on their surface. Improvements in surface free energy of the PP films were observed after corona treatment, around from about 36,9mN=m in films without surface treatment up to 47,9mN=m after 10s of corona discharge when determined by VCG approach / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

Orientador: João Sinezio de Carvalho Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T18:17:28Z (GMT). No. of bitstreams: 1 Buzeto_FabricioAndre_M.pdf: 5022514 bytes, checksum: da17a266de578a2060bb68a4ba3a873d (MD5) Previous issue date: 2007 / Resumo: Estudos das modificações superficiais de polímeros, causadas por descarga corona, são desenvolvidos com o objetivo de mudar as propriedades hidrofóbicas apresentadas por esses materiais, melhorando suas propriedades superficiais sem alterar suas propriedades mecânicas. No presente estudo, realizou-se, alterações na superfície da borracha natural, por tratamento corona de configuração ponta/plano com potência de 5 kV, visando, num segundo momento, a facilitação da incorporação de cargas com caráter hidrofílico à borracha natural. Um planejamento fatorial 22 foi utilizado para a análise dos resultados obtidos por medidas de ângulo de contato, tendo como objetivo a determinação do tempo e altura ótimos para a diminuição do ângulo de contato medido na superfície do polímero em relação à água destilada. Utilizaram-se técnicas complementares como FTIR/ATR, para a determinação das alterações físico-químicas ocorridas na superfície da borracha, bem como, análises térmicas da borracha natural visando à sustentação da não ocorrência de modificações na estrutura polimérica da borracha natural, tais como, reticulações. Através da técnica de microscopia ótica, foi possível verificar que para alturas menores que 2 mm, a superfície da borracha sofre degradação causada pela intensidade das descargas / Abstract: Studies of the superficial modifications of polymers, caused by corona discharges, are developed with the objective to change the hydrophobic properties presented by these materials, improving their superficial properties without changing their mechanical properties. In the present study, superficial modifications were carried out in the natural rubber, for corona treatment from needles-plane electrode system configuration with power of 5 kV, aiming, on a second moment, the facilitation of the incorporation of fillers with hydrophilic characteristic into the natural rubber. A factorial planning 22 was used on the analysis of the results obtained by contact angle measures, taking as an objective the determination of the best time and height for the reduction of the contact angle measured in the polymer surface regarding the distilled water. Complementary techniques were used, like the FTIR/ATR, to determine the chemical-physic alterations taken place in the rubber surface, as well, thermal studies of the natural rubber aiming for sustenance of not-incident modifications in the internal polymeric structure of the natural rubber, such as, reticulations. Through the optical microscopy technique, it was possible to confirm that, for heights less than 2 mm, the rubber surface suffers degradation caused by the intensity of the applied electric charges. / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química