Pulsed electric field (PEF) processing has been demonstrated to be an effective non-thermal pasteurization method for food-treatment applications. With this method, high voltage, short-duration pulses are applied to a chamber through which liquid food is passed. If the voltage applied and the corresponding electric field develops a potential higher than a critical trans-membrane potential, the pores expand, and the membrane of the living cell is ruptured. Due to the lower amount of energy consumed during a PEF process, the temperature of the liquid is kept much lower than as opposed to conventional pasteurization. The PEF method thus kills bacteria and other microorganisms while preserving the nutrition and taste of the liquid foods. Although the parameter responsible for inactivation is the voltage applied, for any given voltage, the conductivity of the liquid defines a current through the liquid that causes the temperature to rise. Therefore, preventing excessive heating of the liquid requires the application of an efficient waveform. According to the literature, the most efficient waveform is a square wave since the entire energy applied would be used for the inactivation process. Although some power supplies are capable of generating such a waveform, the generation of an efficient waveform that satisfies all the requirements for producing a viable product for PEF applications is still a challenging problem. In this research, a cascadable pulse generator, based on a Marx generator design, was designed and implemented in order to generate a pulsed waveform for the treatment of liquid food. IGBT switches were used to charge capacitors in parallel and to discharge them in series as a means of generating a high voltage at the output. The design was implemented and tested for two stages, generating up to 6 kV and 1.6 kA square pulses with a controllable pulse width from 1 µs to 10 µs. Up to 3 switches were connected in parallel to enhance the current capability of the system. Also investigated are ways to improve the transient time by enhancing the IGBT driver circuit. The effect of design parameters such as pulse width, voltage, and current on the temperature rise in the liquid was also studied. A variety of liquid foods with different conductivities were tested in order to confirm the functionality of the system.

This thesis details the design and development of a solid-state, high power modulator for driving plasma ion implantation systems. A plurality of modulators can be stacked in a Marx geometry to allow complete voltage (implantation energy) scalability. Unlike a classic Marx modulator, the design employs actively controlled charging and discharging paths. This allows maximum modulation flexibility and efficiency. A hybrid Marx bank - pulse transformer configuration was commissioned in a 20keV 12A plasma ion implantation system for the purpose of photonics research. <p>The design portion of this work is accompanied by an investigation, extension and discretization of the Lieberman analytical model of plasma ion implantation dynamics. The model predicts final implantation concentrations as well as system operational limits in specific plasma conditions. A new extension to the model accounts for subtle time-of-flight effects on accelerating ions. Agreement between modeled and measured ion currents is good.<p>Finally, a collection of material processing experiments conducted with the plasma ion implantation system since its inauguration in February 2006 is briefly presented. In it, a new silicon-based light emitting diode is introduced.

Quantifying and characterizing isolated tumor cells (ITCs) is of interest in surgical pathology and cytology for its potential to provide data for cancer staging, classification, and treatment. Although the independent prognostic significance of circulating ITCs has not been proven, their presence is gaining clinical relevance as an indicator. However, researchers have not established an optimal method for detecting ITCs. Consequently, this Ph.D. dissertation is concerned with the development and evaluation of dielectric spectroscopy as a low-cost method for cell characterization and quantification. In support of this goal, ultra-wideband (UWB), microwave pulse generator circuits, coaxial transmission line fixtures, permittivity extraction algorithms, and dielectric spectroscopy measurement systems were developed for evaluating the capacity to quantify B16-F10 tumor cells in suspension. First, this research addressed challenges in developing tunable UWB circuits for pulse generation. In time-domain dielectric spectroscopy, a tunable UWB pulse generator facilitates exploration of microscopic dielectric mechanisms, which contribute to dispersion characteristics. Conventional approaches to tunable pulse generator design have resulted in complex circuit topologies and unsymmetrical waveform morphologies. In this research, a new design approach for low-complexity, tunable, sub-nanosecond and UWB pulse generator was developed. This approach was applied to the development of a novel generator that produces symmetrical waveforms (patent pending 60/597,746). Next, this research addressed problems with transmission-reflection (T/R) measurement of cell suspensions. In T/R measurement, coaxial transmission line fixtures have historically required an elaborate sample holder for containing liquids, resulting in high cost and complexity. Furthermore, the algorithms used to extract T/R dielectric properties have suffered from myriad problems including local minima and half-wavelength resonance. In this dissertation, a simple coaxial transmission line fixture for holding liquids by dispensing with the air-core assumption inherent in previous designs was developed (patent pending 60/916,042). In addition, a genetic algorithm was applied towards extracting dielectric properties from measurement data to circumvent problems of local minima and half wavelength resonance. Finally, in this research the capacity for using dielectric properties to quantify isolated B16-F10 tumor cells in McCoy's liquid medium was investigated. In so doing, the utility of the Maxwell-Wagner mixture formula for cell quantification was demonstrated by measuring distinct dielectric properties for differing volumes of cell suspensions using frequency- and time-domain dielectric spectroscopy.

Pulsed electric field (PEF) processing has been demonstrated to be an effective non-thermal pasteurization method for food-treatment applications. With this method, high voltage, short-duration pulses are applied to a chamber through which liquid food is passed. If the voltage applied and the corresponding electric field develops a potential higher than a critical trans-membrane potential, the pores expand, and the membrane of the living cell is ruptured. Due to the lower amount of energy consumed during a PEF process, the temperature of the liquid is kept much lower than as opposed to conventional pasteurization. The PEF method thus kills bacteria and other microorganisms while preserving the nutrition and taste of the liquid foods. Although the parameter responsible for inactivation is the voltage applied, for any given voltage, the conductivity of the liquid defines a current through the liquid that causes the temperature to rise. Therefore, preventing excessive heating of the liquid requires the application of an efficient waveform. According to the literature, the most efficient waveform is a square wave since the entire energy applied would be used for the inactivation process. Although some power supplies are capable of generating such a waveform, the generation of an efficient waveform that satisfies all the requirements for producing a viable product for PEF applications is still a challenging problem. In this research, a cascadable pulse generator, based on a Marx generator design, was designed and implemented in order to generate a pulsed waveform for the treatment of liquid food. IGBT switches were used to charge capacitors in parallel and to discharge them in series as a means of generating a high voltage at the output. The design was implemented and tested for two stages, generating up to 6 kV and 1.6 kA square pulses with a controllable pulse width from 1 µs to 10 µs. Up to 3 switches were connected in parallel to enhance the current capability of the system. Also investigated are ways to improve the transient time by enhancing the IGBT driver circuit. The effect of design parameters such as pulse width, voltage, and current on the temperature rise in the liquid was also studied. A variety of liquid foods with different conductivities were tested in order to confirm the functionality of the system.

Este trabalho descreve o desenvolvimento e a construção de um gerador de pulsos de 8 canais, com interface para controle externo por microcomputador. O gerador possui 16 passos programáveis definindo a largura do pulso entre 200 ns e 10 segundos. Permite também a repetição automática de um intervalo selecionado. O microcomputador tem controle total do gerador de pulsos, incluindo programação de memórias e execução e interrupção de sequências de pulsos. Este gerador foi construído para ser usado em experiências de Ressonância Magnética Nuclear Pulsada, no controle de portas de RF e sistema de detecção / This work describes the development and construction of a 8 channel pulse generator with interface for external microcomputer control. The generator has 16 programmable steps defining pulse widths between 200 nsec and 10 seconds, with 100 nsec resolution. Automatic repeat of a selected step range is also provided. The microcomputer has full control of the pulse generator including programing of memories, execution and interruption of pulse sequences. The generator was built to be used in Pulsed Nuclear Magnetic Resonance experiments to control the high Power RF gate and the detection system

No description available.

Les procédés de traitement de surface sont utilisés à l'échelle industrielle pour améliorer les performances de pièces mécaniques en introduisant des contraintes résiduelles de compression. Cette mise en compression de surface permet de limiter l'amorçage et la propagation de fissures dans le matériau. Ceci permet d'augmenter de façon significative la durée de vie en fatigue des pièces mécaniques ainsi traitées. L'utilisation de ces procédés dans l'industrie a démontré leur efficacité, mais aussi leurs limitations et inconvénients. Les défauts récurrents consistent en une profondeur traitée faible, une dégradation de l'état de surface (rugosité), des difficultés de contrôle, une contamination du matériau traité, etc. Ces défauts ont conduit à l'élaboration de nouveaux procédés innovants qui permettent de meilleures performances en évitant certains des inconvénients succinctement évoqués. Parmi ces procédés innovants, le traitement de surface par impulsion électromagnétique semble particulièrement intéressant. Ce procédé met en œuvre un puissant champ magnétique transitoire pour engendrer des forces de Laplace dans une pièce métallique et induire des contraintes résiduelles. Il n'existe que peu d'informations dans la littérature et il n'existe aucun dispositif expérimental de ce procédé. Cette thèse est dédiée à la conception et la réalisation d'un prototype de mise en compression électromagnétique. Le premier chapitre de cette thèse est un état de l'art des technologies de mise en compression et du procédé de mise en compression par impulsion électromagnétique. Ainsi, les besoins de ce procédé sont identifiés et les technologies pouvant répondre à ces besoins sont explorées. Le deuxième chapitre, après une sélection de la structure globale du dispositif, va consister aux dimensionnements des éléments du prototype EMP. Cette étude commencera avec une étude sur l'inducteur qui va être utilisé avant de continuer sur le dimensionnement du stockage d'énergie et de l'interrupteur de décharge. Afin de valider le dimensionnement des composants précédents, une simulation électromagnétique 3D du système est réalisée. L'assemblage du prototype est présenté dans le troisième chapitre ainsi qu'une première campagne d'essai sur un alliage d'aluminium. Deux types d'éprouvettes sont testées : une éprouvette fine pour vérifier visuellement la mise en compression (essai Almen) et une éprouvette massive afin d'évaluer la profondeur traitée. Une modélisation multiphysique 3D du procédé est réalisée afin de corréler ces résultats avec l'expérience. Dans un dernier chapitre, une étude exploratoire est menée sur un matériau ferromagnétique, le mumétal, pour visualiser l'influence des contraintes résiduelles sur les propriétés magnétiques de ce dernier. / Penning processes are widely used in industries to apply compressive residual stresses into the most solicited part of mechanical pieces. In that way, the compressive residual stresses limit the priming and the propagation of micro-cracks in the material. This increases significantly the lifespan of the treated mechanical piece under fatigue stresses. These existing peening processes have proved their efficiency and also their limitations and weaknesses. The main recurrent defaults are a shallow depth of treatment, a degradation of the surface condition, a random control of the treatment, a material contamination, etc. These problems have led towards the development of news innovative peening processes which allow better performance avoiding some previous defaults briefly evoked. Among these news processes, the electromagnetic peening process seems especially interesting. This process uses high energy electromagnetic fields to induce Lorentz forces into a metallic piece and thus residual stresses. Actually, there is not much information about this process in the literature and no prototype was ever built. The work of this thesis is dedicated to development and realization of an electromagnetic peening prototype. The first chapter of this thesis adresses the state of the art of major peening processes actually in industrial use. Next, the electromagnetic peening process, or EMP process, is described and the electrical needs are exposed. A second state of the art is made about the technological solutions to respond to the EMP needs. The second chapter is about the conception of the EMP prototype with the electrical structure adopted in the previous chapter. The first step is about the inductor sizing to generate an electromagnetic field sufficient enough for a peening application. Next, the storage system is designed depending on the inductor parameters and finally the closing switch is created considering the electrical parameters used for the EMP process. To validate the previous results, a 3D electromagnetic simulation is done. The prototype assembly is presented in the third chapter and also the first experimental test on the EMP prototype. To begin with, an aluminium alloy with low yield strength is selected to be treated. Two different samples forms are used, a thin one, to realize a similar test to the Almen test and thick one to check the EMP depth of treatment. A 3D multiphysics simulation of these experiments is made and these numeric results are next correlated to the experimental ones. In the fourth chapter, an exploratory study is realized on the effects of the residual stresses on magnetic properties of ferromagnetic material, the mumetal

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work in this study covers a powerful technique to derive propagation and scattering information in an expedient fashion. Expedient because time-domain (TD) data gathers a broad spectrum in a single transmitted pulse. TD has been criticised because of a lack of dynamic range, which has now been overcome by the direct sampling system, RATTY and RTA. This study focuses on the investigation of a TD metrology system, to assist with the characterisation of MeerKAT systems. The elementary components of the system include a fast-rising impulse generator that was coupled with an impulse radiating antenna (IRA). The system was calibrated and tested before practical measurements and preliminary testing in the Karoo were done. For TDmetrology a larger bandwidth accelerates measurements without the loss of accuracy. The pulse generator’s (PG’s) fundamental components are an avalanche transistor and a step recovery diode (SRD), to sharpen the leading edge of the pulse. Improving the rise-time of a pulse increases its bandwidth in the spectrum. The external circuitry around these components is pivotal and it determines the shape, amplitude and rise-time of the pulse. In the course of the investigation, the general circuitry around the PG was improved to obtain the best possible pulse for measurements inside a reverberation chamber (RC) and for measurements in the Karoo. In light of this, a second and third PG source were obtained. For measurements in the Karoo, a larger amplitude pulse was required to increase the spectral content and this is essential for propagation measurements over distance and the shielding effectiveness (SE) of structures. Stacking avalanche transistors allow larger amplitude pulses and it improves the dynamic range of the spectrum. A PG incorporating stacked avalanche transistors, was designed, built and measured to assist with RC and small-scale field measurements in the Karoo. The third PG was bought for the practical measurements in the Karoo. The PG produces kilovolt pulses with pico-second rise-times that extend the spectral range of the current PGs at our disposal. With these PGs, an antenna is required for the radiation of impulse-like transients. The IRA is a high-gain large-bandwidth antenna. The IRA consists of a parabolic reflector, conical-plate transmission lines that are terminated through resistors onto the dish, and a feeding balun. The IRA design was thoroughly discussed and a first model for metrology was designed, measured and optimised. The IRA was also simulated with computation software code, FEKO. Before deployment of theTDsystem, calibration and characterisation measurements are required. The measuring devices used within this study were sampling oscilloscopes and direct sampling systems. The limitations of each device were explored and are discussed. The final measurements that were conducted contribute to work related to the SKA. This incorporated antenna pattern calibration, propagation over distance and the SE of a berm built from Karoo soil. The system investigated the propagation attenuation over the Karoo soil and vegetation, with great promise. A broad spectrum was measured over a few kilometres and compared to free-space loss. The SE of the berm covered the same spectral bandwidth. In this measurement, scattering effects and knife-edge diffraction were observed. / AFRIKAANSE OPSOMMING: Die werk in hierdie studie dek ’n kragtige tegniek wat gebruik kan word om die voortplanting en die verstrooiingsinligting van elektromagnetiese golwe op ’n voordelige manier af te lei. Dit is voordelig, want tydgebieddata versamel ’n wye spektrum in ’n enkele oordraagbare puls. Tydgebied is in die verlede baie gekritiseer omdat dit ’n dinamiese reikwydte kortkom en dit is nou oorwin deur die direkte steekproefnemingstelsel, RATTY en RTA. Hierdie studie fokus op die ondersoek van ’n tydgebiedmetingssisteem en dit help met die karakterisering van MeerKAT sisteme. Die elementêre komponente van die sisteem bestaan uit ’n vinnig-stygende impulsgenerator wat gekoppel is aan ’n impulsuitstralende-antenna (IRA). Die sisteem is gekalibreer en getoets voordat praktiese metings en toetse in die Karoo uitgevoer kon word. Vir tydgebiedmetings versnel ’n groter bandwydte die metings sonder om die akkuraatheid daarvan te beïnvloed. Die pulsgenerator se fundamentele komponente is ’n stortvloedtransistor en ’n stap-herstel diode (SRD) wat die voorpunt van die puls verskerp. Die eskterne stroombaan rondom hierdie komponente is noodsaaklik en dit bepaal die vorm, amplitude en die stygtyd van die puls. Deur die loop van hierdie ondersoek is die algemene stroombaan rondom die puls verbeter, om die beste moontlike puls vir metings binne in die weerkaatsingskamer en vir metings in die Karoo, te verkry. Na aanleiding van dit is ’n tweede en derde pulsgenerator bron verkry. Vir die metings in die Karoo is ’n puls met ’n groter amplitude vereis om die spektrale inhoud te vermeerder. Dit is noodsaaklik vir elektromagnetiese golf voortplantingsmetings oor afstand asook die beskermings effektiwiteit (SE) van die strukture. Stapel-stortvloed transistors skep pulse met groter amplitudes en dit verbeter die dinamiese reikwydte van die spektrum. ’n Pulsgenerator wat gestapelde stortvloedtransistors insluit is ontwerp, gebou en gemeet om te help met metings in die weerkaatsingskamer en kleinskaal veldmetings in die Karoo. Die derde pulsgenerator is gekoop vir praktiese metings in die Karoo. Die pulsgenerator vervaardig kilovolt pulse met pikosekond stygtye, wat die reikwydte van die spektrum van ons huidige puls uitbrei. Hierdie pulsgenerators vereis ’n antenna vir die uistraling van impulsagtige seine. Die IRA is ’n hoë-wins, groot-bandwydte antenna. Die IRA bestaan uit ’n paraboliese weerkaatser, konieseplaat transmissielyne wat deur weerstande op die skottel getermineer word, asook ’n voedings "balun". Die IRA ontwerp is deeglik bespreek en ’n model is ontwerp, gemeet en verbeter. Die IRA is ook gesimuleer met behulp van ’n rekenaarsagtewareprogram, FEKO. Voordat die tydgebiedsisteem benut kan word, moet dit gekalibreer word en karakteriseringsmetings moet ook daarmee uitgevoer word. Die meetinstrumente wat in hierdie studie gebruik is, is steekproefneming-ossilloskope en direkte steekproefneming-sisteme. Die tekortkominge van elke instrument is ondersoek en bespreek. Die finale meting wat uitgevoer is, dra by tot die werk wat geassosieer word met die SKA. Dit behels antennapatroonkalibrasie, voortplanting van elektromagnetiese golwe oor afstand en die SE van ’n "berm"wat gebou is uit Karoo-grond. Hierdie sisteem is gebruik om die voortplantings-verswakking oor die Karoo-grond en plantegroei te ondersoek en dit lyk baie belowend. ’nWye spektrumis oor ’n paar kilometer gemeet en dit is met wrywinglose ruimte vergelyk. Die SE van die "berm"het dieselfde spektrale bandwydte gedek. In hierdie meting is verstrooiingseffekte en mespunt-diffraksie waargeneem.

Orientador: Jose Antenor Pomilio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-06T14:09:31Z (GMT). No. of bitstreams: 1 Rondani_Bruno_M.pdf: 5870538 bytes, checksum: 69f2b2bd154400cd5b620b87a2c4fe8c (MD5) Previous issue date: 2005 / Resumo: Descreve-se neste trabalho o desenvolvimento de uma topologia de modulador de pulso estado-sólido e a linha de retardo modular, para aplicação em transmissores pulsados de alta potência que utilizem válvulas de microondas magnetron empregadas comumente em radares de trajetografia, meteorologia e controle de tráfego aéreo. A pesquisa abrange o projeto, desenvolvimento e construção de um modulador de pulso destinado à modernização do transmissor do radar de trajetografia Bearn do Centro de Lançamentos de Foguetes da Barreira do Inferno, Natal -RN. O equipamento desenvolvido fornece pulsos de até 37,5kV e 60A em três modos de transmissão, a saber: monopulso longo, monopulso curto e bipulso. No modo monopulso longo, a largura de pulso é de 1,7µs e nos outros dois modos, 0,85µs. A taxa de repetição dos pulsos é de 585,5Hz. A unidade de modulação de pulso consiste de oito módulos de chaveamento em paralelo, conectados ao primário de um transformador de pulso de razão 1:50. Cada módulo contém dois trechos de linha de retardo e duas chaves estado-sólido e é capaz de gerar pulsos de até 790V e 390A nos diferentes modos de operação. A alimentação da linha de retardo é feita através de um circuito de carga composto por um indutor de alimentação e um circuito de Clipper. O indutor de alimentação faz com que a tensão de carga na linha seja dobrada em relação à tensão contínua presente na saída da fonte de alimentação de entrada, devido à ressonância série criada entre esse indutor e a capacitância total das linhas de retardo. O circuito de Clipper garante a regulação de tensão pulso a pulso e a proteção do modulador contra surto de sobre-corrente na carga e sobre-tensão nas linhas de retardo. Esta topologia foi desenvolvida para melhorar a confiabilidade e facilitar a manutenção dos transmissores de radar com a implementação do conceito de degradação suave (graceful degradation) do modulador de pulso / Abstract: This work describes the development of a modular line-type solid-state pulse modulator topology to be applied in magnetron pulsed power radar transmitters, commonly found on tracking, weather and air traffic management radars. This research includes the design, development and assembling of a pulsed modulator for the Barreira do Inferno Launching Center (CLBI, Natal-RN) Bearn tracking radar upgrade program. The equipment developed provides pulses of 37.5 KV and 60 A in three transmission modes: single long pulse, single short pulse and bipulse. In the single long pulse the pulse width is 1.7 µs and in the other modes 0.85 µs. The pulse repetition frequency is of 585.5Hz. The modulator unit is composed by eight switching modules connected in parallel with the primary windings of a 1:50 ratio pulse transformer. Each module has two pulse-forming network and two IGBT switches and it is capable of handling 790 V and 390 A in the three operational modes. An inductor and a Clipper circuit implement the pulse-forming network charging. The charging inductor allows charging the pulse-forming network with twice the supply voltage since there is a resonance with the total modulator capacitance. The Clipper circuit assures the pulse-to-pulse charging voltage regulation and protects the modulator against load over-current and over-voltage charging. This topology was developed to improve reliability and maintainability of radar transmitters by implementing the graceful degradation (soft failure mode) in the pulse modulator / Mestrado / Sistemas e Controle de Energia / Mestre em Engenharia Elétrica

<p>Impulsni generator predstavlja jedan od najvažnijih delova bežičnog<br />primopredajnika. Pored toga što treba da generiše signal čiji<br />spektar zadovoljava odgovarajuću spektralnu masku, generator treba da<br />bude što jednostavniji, zauzima malu površinu i ima malu potrošnju.<br />Naučni doprinos ove doktorske disertacije predstavlja sedam novih<br />konfiguracija ultra-širokopojasnih impulsnih generatora<br />projektovanih u CMOS tehnologiji, od kojih su tri fabrikovane u<br />0,18 &mu;m UMC CMOS procesu. Prvi dizajn je zasnovan na principu<br />kombinovanja kratkotrajnih impulsa, sledeća tri sadrže ring<br />oscilator, naredna dva impulsna generatora koriste princip<br />filtriranja, dok poslednje novo rešenje obezbeđuje BPSK kodovanje<br />korišćenjem dva ring oscilatora.</p> / <p>Pulse generator is one of the most important parts of a wireless transceiver.<br />Besides generating a signal which spectrum has to satisfy corresponding<br />spectral mask, the pulse generator should have topology as simple as<br />possible, consume low power and occupy low die-area. Scientific contribution<br />of this dissertation are seven novel IR-UWB pulse generator architectures<br />designed in CMOS technology of which three are fabricated in 0.18 &mu;m UMC<br />CMOS process. The first design is based on combining very short pulses, the<br />next three contain a ring oscillator topology followed by two pulse generators<br />that use the filtering approach, while the last new solution enables BPSK<br />modulation by employing two ring oscillator topologies.</p>