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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

Avaliação de técnicas alternativas para o manejo da antracnose da banana em pós-colheita

PESSOA, Wagner Rogério Leocádio Soares 13 March 2009 (has links)
Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-27T16:34:00Z No. of bitstreams: 1 Wagner Rogerio Leocadio Soares Pessoa.pdf: 794895 bytes, checksum: fa791ef69e88320cf4072254f9211112 (MD5) / Made available in DSpace on 2017-03-27T16:34:00Z (GMT). No. of bitstreams: 1 Wagner Rogerio Leocadio Soares Pessoa.pdf: 794895 bytes, checksum: fa791ef69e88320cf4072254f9211112 (MD5) Previous issue date: 2009-03-13 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The banana is the second fruit more consumed in the world, being the fruit fresh holder of larger world market. Brazil, answers as second producing adult, using the varieties Silver and Pacovan in approximately 60% of area harvestd. However, several factors can cause losses in the production. In the powder-crop to the anthracnose, caused by Colletotrichum musae, it is the main and more destructive, harming the commercialization. Before that, the present work concerns the evaluations of alternative methods of control that seek to the reduction of the losses powder-crop in bananas caused by the C. musae. The first work is had the effect of resistance inductors in the control powder-crop of the anthracnose in banana.Among the tested inductors they are had the Acibenzolar-S-methyl (ASM), Agriculture-Mós®, Ecolife®, Crop-Set®, methyl jasmonate, were applied in the dosage recommended by the manufacturer (DR) and DR added of 50% there is plus, for five minutes of immersion, the inoculations were accomplished under the times of zero, six and 12 hours after the induction. In the second rehearsal the production of the enzymes was evaluated: peroxidase, polifenoloxidase, quitinase, β-1,3-glucanase and β -1,4-glucanase under bananas induce with biotic elicitores and abióticos. The third experiment, concerns the thermotherapy (TH) associate to ASM in the control of the anthracnose. Where bouquets were treated by immersion in warm water to 40, 45, 50 and 55 ± 1 ºC, for the times of zero, five, 10 and 15 minutes, parallel to these treatments the bouquets were immersed in syrup containing ASM, for five minutes, in the DR for the manufacturer. In relation to the fourth work, the effect of dosages zero 50, 150, 300 and 450 nL.L-1 of 1-MCP on the banana anthracnose was verified. The inoculations of all of the works were accomplished with a suspension of conidial of C. musae in the concentration 106 con./mL, deposited on the epidermis previously wounded. At the end of each rehearsal they were appraised the banana's physiochemical characteristics except for the second. ASMapplied 12 hours before the inoculation in the added of 50% commercial dosage there is plus, it was the most efficient in the control of the disease. In relationship, to enzymes peroxidase, polifenoloxidase β -1,3-glucanase and β -1,4-glucanase, AGM and MJ the most efficient inductors were in the production of these enzymes, in relation to the quitinase AGM did just stand out in relation to the others. To the temperatures around of 40 and 45 ºC in all of the times of exhibition tested were the most expressive in the reduction of the severity in relationship á testifies. In TH + ASM, for the temperatures from 45 to 50 °C in all of the times of exhibition and 40 °C in the times of 10 and 15 minutes presented smaller severity of the disease in relation to isolated TH. In the 1-MCP, the dosages of 150 and 50 nL.L-1 they presented the smallest severity values with 9,57 and 9,67 mm, respectively, following for the dosage of 300 and 450 nL.L-1 with 10,18 to 10,5 mm. The witness presented the largest severity with 32,04 mm being reduced in the progressive largest way for to smallest dosage.It didn't happen significant changes in the pH, SST and ATT, that commit the commercialization and the banana's consumption in natura. / A banana (Musa spp.)é a segunda fruta mais consumida no mundo, sendo a fruta fresca detentora de maior mercado mundial. O Brasil, responde como segundo maior produtor, utilizando as cvs. Prata e Pacovan em aproximadamente 60 % de sua área cultivada. Contudo, diversos fatores podem ocasionar perdas na produção. Na pós-colheita à antracnose, causada por Colletotrichum musae, é a principal e mais destrutiva, prejudicando a comercialização. Diante disso, o presente trabalho tem por objetivo avaliar métodos alternativos de controle que visem à redução das perdas pós-colheita em bananas causada por C. musae. O primeiro artigo tem-se o efeito de indutores de resistência no controle pós-colheita da antracnose em banana. Foram avaliados os indutores acibenzlar-S-metil (ASM), Agro-Mós®, Ecolife®, Crop- Set®, metil jasmonato, sendo aplicado na dosagem recomendada (DR) pelo fabricante e DR acrescido de 50 %, por cinco minutos de imersão. As inoculações com o isolado Cm 10 foram realizadas sob os tempos de zero, seis e 12 horas após a indução. No segundo artigo, avaliou-se a produção das enzimas peroxidase, polifenoloxidase, quitinase, β-1,3-glucanase e β-1,4- glucanase sob bananas induzidas com elicitores bióticos e abióticos. O terceiro artigo, diz respeito ao tratamento hidrotérmico (TH) associado ao ASM no controle da antracnose. Onde buquês foram tratados por imersão em água aquecida a 40, 45, 50 e 55 ± 1 ºC, pelos tempos de zero, cinco, 10 e 15 minutos. Paralelo ao tratamento TH, os buquês foram imersos em calda contendo o ASM, por cinco minutos, na DR do fabricante. Em relação ao quarto artigo, verificou-se o efeito de dosagens 0, 50, 150, 300 e 450 nL.L-1 de 1-MCP sobre a antracnose da banana. As inoculações de todos os trabalhos foram realizadas com suspensão de conídios de C. musae na concentração de 106 con./mL, depositado sobre a epiderme previamente ferida. Ao final de cada ensaio foram avaliadas as características físico-químicas da banana com exceção do segundo experimento. O ASM e o AGM aplicado 12 horas antes dainoculação na dosagem comercial acrescido de 50 %, foram o mais eficientes no controle da doença. Em relação as enzimas peroxidase, polifenoloxidase, β-1,3-glucanase e β-1,4- glucanase, o AGM e o MJ foram os indutores mais eficientes em sua produção. Para a quitinase apenas o AGM destacou-se em relação aos demais. Às temperaturas ao redor de 40 a 45 ºC em todos os tempos de exposição testados foram as mais expressivas na redução da severidade da doença em relação á testemunha. No TH + ASM, para as temperaturas de 45 a 50 °C em todos os tempos de exposição e 40 °C nos tempos de 10 e 15 minutos apresentaram menor severidade da doença em relação ao TH isolado. No 1-MCP as dosagens de 150 e 50 nL.L-1 apresentaram os menores valores de severidade com 9,57 e 9,67 mm, respectivamente. Não ocorreram mudanças significativas no pH, SST e ATT, que comprometessem a comercialização e o consumo in natura da banana.
112

Digital average-current control for the dual interleaved boost converter

Villarruel-Parra, Alejandro January 2015 (has links)
This Thesis addressed the challenge of ensuring balanced currents in the phases of a multi-kW, interleaved dc-dc converter by means of closed-loop digital control. The Thesis examines uniformly-sampled, valley-current, peak-current and average-current control for a dual interleaved boost converter with inter-phase transformer which might form part of the power train of an electric vehicle. Also, an enhancement of the average-current control is investigated in which the transistor duty-ratio is updated more rapidly, which allows an improvement of approximately ten times in the response speed of the system. Based on the theoretical analysis, the average-current control methodology was determined to be the most suitable technique for this type of converter as it ensures well-balanced phase currents over a wide range. To provide a basis for control system analysis and design for interleaved converters, a modelling methodology is developed based on a combination of multi-rate data-sampled theory and a small-signal averaged converter model. The model is shown to represent accurately the interaction between the interleaved phases, revealing a reduced stability range compared with a non-interleaved converter. The modelling and control methods are validated using switched and average value simulations obtained with the SABER software and by experimental results from a 25 kW, 30 kHz converter prototype. The control techniques were implemented on a Texas Instruments TMS320F28335 digital signal controller.
113

Ultra compact multi-standard low-noise amplifiers in 28 nm CMOS with inductive peaking

Sobotta, Elena, Belfiore, Guido, Ellinger, Frank 04 June 2020 (has links)
This work presents the design of two compact multi-standard low-noise amplifier (LNA) in a 28 nm low-power bulk CMOS process. The transistor parameters were optimized by the Gₘ/ID method taking into account the parasitics and the behavior of highly scaled transistors. To cover the industrial science medical (ISM)-bands around 2.4 and 5.8 GHz, the WLAN band as well as the Kᵤ band a bandwidth enhancement is required. Two versions of LNAs, one with vertical inductors and one with active inductors, are implemented and verified by measurements. The noise figure (NF) exhibits 4.2 dB for the LNA with active inductors and 3.5 dB for the LNA with vertical inductors. The voltage gain reaches 12.8 and 13.4 dB, respectively, with a 3 dB-bandwidth of 20 GHz. Both input referred 1-dB-compression points are higher than 212 dBm making the chips attractive for communication standards with high linearity requirements. The chips consume 53 mW DC power and the LNA with active inductors occupies a core area of only 0.0018 mm², whereas the version with vertical inductors requires 0.021 mm².
114

Analysis of a high step-up gain DC-DC converter for fuel cell and battery application

Törngren Sato, Kaj January 2023 (has links)
In sustainable energy systems those using fuel cells, high step-up gain converters are widely used to increase the output voltage to levels that can be used by other converters, such as inverters for grid connection or powering other AC loads. In order to obtain a higher voltage gain, in comparison to a traditional boost converter, often different topologies techniques are involved. In this project a new topology is studied, cascading to half bridges, each working similar to a boost converter but with magnetic coupled inductors in-between.    The converter design is modeled in PLECS Blockset and MATLAB Simulink to simulate and evaluate the performance with proper design procedure. The results showed that a high step-up gain was achieved, and the gain could easily be adjusted by changing the duty cycle and/or the coupling factor. The converter design showed similarities and differences to a traditional boost converter. The coupled inductor has its advantage reducing the fuel cell current ripple with the effect of the duty cycle.
115

A novel DC-DC converter for photovoltaic applications

Nathan, Kumaran Saenthan January 2019 (has links)
Growing concerns about climate change have led to the world experiencing an unprecedented push towards renewable energy. Economic drivers and government policies mean that small, distributed forms of generation, like solar photovoltaics, will play a large role in our transition to a clean energy future. In this thesis, a novel DC-DC converter known as the Coupled Inductors Combined Cuk-SEPIC' (CI-CCS) converter is explored, which is particularly attractive for these photovoltaic applications. A topological modification is investigated which provides several benefits, including increased power density, efficiency, and operational advantages for solar energy conversion. The converter, which is based on the combination of the Cuk and SEPIC converters, provides a bipolar output (i.e. both positive and negative voltages). This converter also offers both step-up and step-down capabilities with a continuous input current, and uses only a single, ground-referenced switching device. A significant enhancement to this converter is proposed: magnetic coupling of the converter's three inductors. This can substantially reduce the CI-CCS converter's input current ripple - an important benefit for maximum power point tracking (MPPT) in photovoltaic applications. The effect of this coupling is examined theoretically, and optimisations are performed - both analytically and in simulations - to inform the design of a 4 kW prototype CI-CCS converter, switched at a high frequency (100 kHz) with a silicon carbide (SiC) MOSFET. Simulation and experimental results are then presented to demonstrate the CI-CCS converter's operation and highlight the benefits of coupling its inductors. An efficiency analysis is also undertaken and its sources of losses are quantified. The converter is subsequently integrated into a domestic photovoltaic system to provide a practical demonstration of its suitability for such applications. MPPT is integrated into the CI-CCS DC-DC converter, and a combined half bridge/T-type converter is developed and paired with the CI-CCS converter to form an entirely transformerless single-phase solar energy conversion system. The combination of the CI-CCS converter's bipolar DC output with the combined half bridge/T-type converter's bipolar DC input allows grounding at both the photovoltaic panels and the AC grid's neutral point. This eliminates high frequency common mode voltages from the PV array, which in turn prevents leakage currents. The entire system can be operated in grid-connected mode - where the objective is to maximise power extracted from the photovoltaic system, and is demonstrated in stand-alone mode - where the objective is to match solar generation with the load's power demands.
116

Broadband Phase Shifter Realization With Surface Micromachined Lumped Components

Tokgoz, Korkut Kaan 01 September 2012 (has links) (PDF)
Phase Shifters are one of the most important building cells of the applications in microwave and millimeter-wave range, especially for communications and radar applications / to steer the main beam for electronic scanning. This thesis includes all of the stages starting from the theoretical design stage to the measurements of the phase shifters. In detail, all-pass network phase shifter configuration is used to achieve broadband and ultra wide-band differential phase characteristics. For these reasons, 1 to 2 GHz, 2 to 4 GHz, and 3 to 6 GHz 4-bit, 22.5&deg / phase resolution phase shifter realization with surface micromachined lumped components are designed, simulated, fabricated and measured. Basic building blocks of the phase shifters, i.e., surface micromachined lumped components, square planar spiral inductors and Metal-Insulator-Metal capacitors are designed with EM simulation and lumped equivalent model extractions. The validation of the designed square planar spiral inductors is done with fabrication and measurement steps, very low error, below 1%, between the designs and fabricated samples are observed. Using this knowledge on lumped elements finally phase shifters are designed with surface micromachined lumped components, fabricated using an in house technology provided by METU-MEMS facilities, RF MEMS group. Low phase rms error, good return and insertion loss considerations are aimed, and achieved. In addition to the main work of this thesis, a generalized theoretical calculation method for 2n-1 number of stages all-pass network phase shifters is presented for the first time in literature. A different, new, broadband, and combined phase shifter topology using two-stage all-pass filters is presented. Moreover, the implementation of this idea is proved to be practical to 3 to 6 GHz 5.625&deg / and 11.25&deg / combined phase shifter. A new approach for stage numbers other than power of 2 is indicated, which is different from what is already presented in the literature. An example practical implementation results are provided for the three-stage 4-bit 1 to 6 GHz phase shifter. Also, a small improvement in SRF of the high inductance valued inductors is achieved with the mitering of the corners of square planar spiral inductors. Comparison of the measured data between the normal inductors and mitered versions shows that the first SRF of the inductors are increased about 80 MHz, and second SRF of the inductors are increased about 200 MHz.
117

Improvement of strategies for the management of fire blight (Erwinia amylovora). Evaluation and optimization of physical and chemical control methods, and use of decision support systems

Ruz Estévez, Lídia 03 November 2003 (has links)
El foc bacterià és una malaltia que afecta a plantes de la família de la rosàcies, causada pel bacteri Erwinia amylovora. El seu rang d'hostes inclou arbres fruiters, com la perera, la pomera o el codonyer, i plantes ornamentals de gran interès comercial i econòmic. Actualment, la malaltia s'ha dispersat i es troba àmpliament distribuïda en totes les zones de clima temperat del món. A Espanya, on la malaltia no és endèmica, el foc bacterià es va detectar per primer cop al 1995 al nord del país (Euskadi) i posteriorment, han aparegut varis focus en altres localitzacions, que han estat convenientment eradicats. El control del foc bacterià, és molt poc efectiu en plantes afectades per la malaltia, de manera que es basa en mesures encaminades a evitar la dispersió del patogen, i la introducció de la malaltia en regions no endèmiques. En aquest treball, la termoteràpia ha estat avaluada com a mètode d'eradicació d'E. amylovora de material vegetal de propagació asimptomàtic. S'ha demostrat que la termoteràpia és un mètode viable d'eradicar E. amylovora de material de propagació. Gairebé totes les espècies i varietats de rosàcies mantingudes en condicions d'humitat sobrevivien 7 hores a 45 ºC i més de 3 hores a 50 ºC, mentre que més d'1 hora d'exposició a 50 ºC amb calor seca produïa danys en el material vegetal i reduïa la brotació. Tractaments de 60 min a 45 ºC o 30 min a 50 ºC van ser suficients per reduir la població epífita d'E. amylovora a nivells no detectables (5 x 102 ufc g-1 p.f.) en branques de perera. Els derivats dels fosfonats i el benzotiadiazol són efectius en el control del foc bacterià en perera i pomera, tant en condicions de laboratori, com d'hivernacle i camp. Els inductors de defensa de les plantes redueixen els nivells de malaltia fins al 40-60%. Els intervals de temps mínims per aconseguir el millor control de la malaltia van ser 5 dies pel fosetil-Al, i 7 dies per l'etefon i el benzotiadiazol, i les dosis òptimes pel fosetil-Al i el benzotiadiazol van ser 3.72 g HPO32- L-1 i 150 mg i.a. L-1, respectivament. Es millora l'eficàcia del fosetil-Al i del benzotiadiazol en el control del foc bacterià, quan es combinen amb els antibiòtics a la meitat de la dosi d'aquests últims. Tot i que l'estratègia de barrejar productes és més pràctica i fàcil de dur a terme a camp, que l'estratègia de combinar productes, el millor nivell de control de la malaltia s'aconsegueix amb l'estratègia de combinar productes. Es va analitzar a nivell histològic i ultrastructural l'efecte del benzotiadiazol i dels fosfonats en la interacció Erwinia amylovora-perera. Ni el benzotiadiazol, ni el fosetil-Al, ni l'etefon van induir canvis estructurals en els teixits de perera 7 dies després de la seva aplicació. No obstant, després de la inoculació d'E. amylovora es va observar en plantes tractades amb fosetil-Al i etefon una desorganització estructural cel·lular, mentre que en les plantes tractades amb benzotiadiazol aquestes alteracions tissulars van ser retardades. S'han avaluat dos models (Maryblyt, Cougarblight) en un camp a Espanya afectat per la malaltia, per determinar la precisió de les prediccions. Es van utilitzar dos models per elaborar el mapa de risc, el BRS-Powell combinat i el BIS95 modificat. Els resultats van mostrar dos zones amb elevat i baix risc de la malaltia. Maryblyt i Cougarblight són dos models de fàcil ús, tot i que la seva implementació en programes de maneig de la malaltia requereix que siguin avaluats i validats per un període de temps més llarg i en àrees on la malaltia hi estigui present. / Fire blight, caused by the bacterium Erwinia amylovora, is a serious disease of rosaceous plants that affects fruit trees such as pear, apple or quince, and ornamental plants with great commercial and economic interest. The disease is spread and well distributed in all temperate regions of the world. In Spain, where the disease is non endemic, fire blight was first detected in 1995 in the North of the country (Euskadi) and later, several new outbreaks have appeared in other locations that have been properly eradicated. Control of fire blight is very slightly effective in affected plants and is based on measures to avoid the spread of pathogen, and the introduction of disease in non-endemic regions. In this work, thermotherapy has been evaluated as a method for eradication of E. amylovora from symptomless propagating plant material. It has been demonstrated that heat is a viable method for eradicating E. amylovora from the propagation material of the pear. Almost all rosaceous species and cultivars maintained under moist conditions survived 7 hours at 45 ºC and up to 3 hours at 50 ºC, while more than 1 hour of exposure at 50 ºC under dry heat injured plants and reduced shooting. However, 60 min at 45 ºC or 30 min at 50 ºC were enough to reduce epiphytic E. amylovora population on pear budwoods to non-detectable level (5 x 102 cfu g-1 f.w.). Phosphonate derivatives and benzothiadiazole were effective in fire blight control in pear and apple, under laboratory, greenhouse and field conditions. Plant defense inducers reduced disease levels to 40-60%. The minimal time intervals to achieve the best control of disease were 5 days for fosetyl-Al, and 7 days for ethephon and benzothiadiazole, and the optimal doses of fosetyl-Al and benzothiadiazole were 3.72 g HPO32- L-1 and 150 mg a.i. L-1, respectively. The efficacy of fosetyl-Al and benzothiadiazole in fire blight control was improved when consecutively sprayed (combined strategy) with a half-reduced dose of antibiotics. Although the mixed strategy is more practical and easier to apply in the orchard than the combined one, the best level of fire blight control was achieved with the combined strategy. The effect of benzothiadiazole and phosphonates in Erwinia amylovora-pear interaction was analyzed at histological and ultrastructural level. Neither benzothiadiazole, nor fosetyl-Al, nor ethephon induced structural changes in pear leaf tissues 7 days after their application. However, after E. amylovora inoculation structural cell disorganization was observed in fosetyl-Al and ethephon-sprayed plants, while in benzothiadiazole-sprayed plants these tissue alterations were delayed. Two predictive models (Maryblyt and Cougarblight) were evaluated in an orchard naturally affected by fire blight in Spain, to determine the accuracy of the predictions. The combined BRS-Powell model and the modified BIS95 model were also evaluated. Results showed two clearly differentiated geographical areas with high and low fire blight risk. Maryblyt and Cougarblight are easy models to use, but their implementation in disease management programs must be evaluated and validated for more seasons and in areas where the disease is present.
118

LC-tank CMOS Voltage-Controlled Oscillators using High Quality Inductor Embedded in Advanced Packaging Technologies

Yoon, Sangwoong 19 November 2004 (has links)
This dissertation focuses on high-performance LC-tank CMOS VCO design at 2 GHz. The high-Q inductors are realized using wiring metal lines in advanced packages. Those inductors are used in the resonator of the VCO to achieve low phase noise, low power consumption, and a wide frequency tuning range. In this dissertation, a fine-pitch ball-grid array (FBGA) package, a multichip module (MCM)-L package, and a wafer-level package (WLP) are incorporated to realize the high-Q inductor. The Q-factors of inductors embedded in packages are compared to those of inductors monolithically integrated on Si and GaAs substrates. All the inductors are modeled with a physical, simple, equivalent two-port model for the VCO design as well as for phase noise analysis. The losses in an LC-tank are analyzed from the phase noise perspective. For the implementation of VCOs, the effects of the interconnection between the embedded inductor and the VCO circuit are investigated. The VCO using the on-chip inductors is designed as a reference. The performance of VCOs using the embedded inductor in a FBGA and a WLP is compared with that of a VCO using the on-chip inductor. The VCO design is optimized from the high-Q perspective to enhance performance. Through this optimization, less phase noise, lower power consumption, and a wider frequency tuning range are obtained simultaneously.
119

Integrated CM Filter for Single-Phase and Three-Phase PWM Rectifiers

Hedayati, Mohammad Hassan January 2015 (has links) (PDF)
The use of insulated-gate bipolar transistor (IGBT)-based power converters is increasing exponentially. This is due to high performance of these devices in terms of efficiency and switching speed. However, due to the switching action, high frequency electromagnetic interference (EMI) noises are generated. Design of a power converter with reduced EMI noise level is one of the primary objectives of this research. The first part of the work focuses on designing common-mode (CM) filters, which can be integrated with differential-mode (DM) filters for three-phase pulse-width modulation (PWM) rectifier-based motor drives. This work explores the filter design based on the CM equivalent circuit of the drive system. Guidelines are provided for selection of the filter components. Different variants of the filter topology are evaluated to establish the effectiveness of the proposed topology. Analytical results based on Bode plot of the transfer functions are presented, which suggest effective EMI reduction. Experimental results based on EMI measurement on the grid side and CM current measurement on the motor side are presented. These results validate the effectiveness of the filter. In the second part of the work, it is shown that inclusion of CM filters into DM filters results in resonance oscillations in the CM circuit. An active damping strategy is proposed to damp the oscillations in both line-to-line and line-to-ground ac voltages and currents. An approach based on pole placement by state feedback is used to actively damp both the DM and CM filter oscillations. Analytical expressions for state-feedback controller gains are derived for both continuous-and discrete-time models of the filter. Trade-off in selection of the active damping gain on the lower-order grid current harmonics is analysed using a weighted admittance function method. In the third part of the work, single-phase grid-connected power converters are considered. An integrated CM filter with DM LCL filter is proposed. The work explores the suitability of PWM methods for single-phase and parallel single-phase grid-connected power converters. It is found that bipolar PWM and unipolar PWM with 180◦interleaving angle are suitable for single-phase and parallel single-phase power converters, respectively. The proposed configuration along with the PWM methods reduces the CM voltage, CM current, and EMI noise level effectively. It is also shown that the suggested circuit is insensitive to nonidealities of the power converter such as dead-time mismatch, mismatch in converter-side inductors, unequal turn on and turn off of the switches, and propagation delays. In the fourth part of the work, the inter-phase inductor in parallel interleaved power converters is integrated with LCL filter boost inductor. Different variant designs are presented and compared with the proposed structure. It is shown that the proposed structure makes use of standard core geometries and consumes lesser core material as well as copper wire. Hence, it reduces the overall size and cost of the power converter. In the present work, a 10kVA three-phase back-to-back connected with input LCL filter and output dv/dt filter, a 5kVA single-phase grid-connected power converter with LCL filter, and a 7.5kVA parallel single-phase grid-connected power converter with LCL filter are fabricated in the laboratory to evaluate and validate the proposed methods. The experimental results validate the proposed methods that result in significant EMI performance improvement of grid-connected power converters.
120

Development of CMOS-Compatible, Microwave-Assisted Solution Processing of Nanostructured Zine Ferrite Films for Gigahertz Circuits

Sai, Ranajit January 2013 (has links) (PDF)
The development of radio frequency integrated circuits (RFICs), especially the dream of integrating analog, digital and radio frequency (RF) components on the same chip that is commonly known as System-on-a-Chip (SoC), is crucial to mobile communications of the future. Such SoC approach offers enhanced performance, greater reliability, and substantially less power consumption of integrated circuits while reducing overall physical size and thus manufacturing cost. However, the progress has been stalled by the lack of miniaturized inductor elements. Rise of unwanted parasitic effects limits down-scaling of the inductor structures and leaves the use of magnetic coating as a viable and attractive option to enhance the inductance and thus inductance density. It is also essential to shift from perm alloy and other amorphous alloys to ferrites and hex ferrites as the core material because of their very high electrical resistivity so as to keep losses in check, a criterion that cannot be compromised on in GHz frequency applications. This is viable, however, only if the integration of the magnetic core (film), particularly a ferrite film, is fully compatible with the CMOS fabrication process. Various approaches have been taken to meet this requirement, including investigations of employing layers of ferrite materials to envelop the inductor loop. However, the deposition of thin films of ferrites, whether by PVD or CVD, usually calls for the deposited ferrite layer to be annealed at an elevated temperature to crystallize the layer so that its magnetic characteristics are appropriate for the optimum performance of the circuit element. Such annealing is incompatible with CMOS process flow required for aggressive device geometries, as the inductor element is added after the active semiconductor circuit is processed, and any exposure of the processed circuit to elevated temperatures risks disturbing precise doping profiles employed and the integrity of the inter-layer dielectrics. What is called for is a low-temperature process for the deposition of a ferrite layer on top of the patterned inductor element – a layer of thickness such that most of the fringe field is encapsulated – while ensuring that the layer comprises crystallites of uniform size that leads to uniform magnetic behaviour. Recognizing the difficulty of meeting the various stringent requirements, it has recently been remarked that such a goal is a formidable challenge. In an attempt to address this challenge, in this work, we have adopted a counter-intuitive approach - the deposition of the desired ferrite composition on a processed die (that contains the inductor structures along with active semiconductor circuits) by immersing it into a chemical (reactant) solution, followed by a brief irradiation of microwave frequency. However, to identify the desired ferrite composition and the appropriate recipe to deposit them, a systematic effort had to be made first, to understand the inter-relationship between synthesis process, structure of resulting material, and its physical and chemical properties. Therefore, at the beginning, a general introduction in which key concepts related to the magnetic-core inductors, the microwave-irradiation-assisted synthesis of nanostructures, the ‗state of the art‘ in the field of integration of appropriate magnetic material to the RFICs, are all outlined. As a proof of concept, microwave-irradiation-assisted solution-based deposition of zinc ferrite thin films on the technologically important Si (100) substrate is demonstrated. The highlight of the process is the use of only non-toxic metal organic precursors and aqua-alcoholic solvents for the synthesis, which is complete in 10 minutes @< 100 °C, without any poisonous by-products. Effects of various process parameters such as solute concentrations, surfactant types, and their concentrations are investigated. A wide range of deposition rates (10 - 2000 nm/min) has been achieved by tweaking the process parameters. The simultaneous formation of zinc ferrite nanocrystallites (ZFNC) along with deposition of thin film is the hallmark of this synthesis technique. Unlike its bulk counterpart, both film and powder are found upon investigation to be rich in magnetic behavior– owing to plausible cationic distribution in the crystal lattice, induced by the inherently quick and far-from-equilibrium nature of the process. The accurate estimation of magnetic characteristics in film is, however, found to be difficult due to the high substrate-to-film mass ratio. The simultaneously prepared ZFNC is examined to arrive at the optimized process recipe that imparts the desired magnetic properties to the zinc ferrite system. The crystallographic cationic distribution in zinc ferrite powder is, however, difficult to study due to the nanoscale dimension of the as prepared material. To enable crystal growth, slow and rapid annealing in air at two different temperatures are employed. The effects of these annealing schemes on various attributes (magnetic properties in particular) are studied. Rapid annealing turns out to be an interesting pathway to promote rapid grain-growth without disturbing the crystallographic site occupancies. The presence of inversion, i.e., the amount of Fe3+ in the ‗A‘-sites in the spinel structure that ideally is zero in normal spinel structure of zinc ferrite, is evident in all annealed ZFNC, as determined by Riveted analysis. Such partially inverted ZFNC exhibits soft magnetic behavior with high saturation magnetization, which can easily be ―tuned‖ by choosing appropriate annealing conditions. However, a few unique strategic modifications to the same microwave-irradiation-assisted solution-based synthesis technique are tried for the formation of nanocrystalline powder with desired sizes and properties without the necessity of anneal. The approach eventually appears to pave a way for the formation of oriented structures of zinc ferrite. The effects of anneal, nevertheless, are studied with the help of neutron powder diffractometry and magnetic measurements. The magnetic ordering at various temperatures is analyzed and connected to the magnetic measurements. The study shows that long-range magnetic ordering, present even at room temperate, originates from the distribution of cations in the partially inverted spinel structures, induced by the rapid and kinetically driven microwave synthesis. Keeping the mild nature (<200 °C) of the processing in mind, a large degree of inversion (~0.5) is a surprise and results in a very high saturation magnetization, as much as 30 emu/g at room temperature (paramagnetic in bulk), in the ZFNC system. Based on the knowledge of process-structure-property interrelationship, a recipe for the deposition of ferrite thin films by the microwave-assisted deposition technique is optimized. Successful deposition of smooth and uniform zinc ferrite thin films on various substrates is, then, demonstrated. The mystery behind the strong adherence of the film to the substrate - an unexpected outcome of a low-temperature process - is probed by XPS and the formation of silicates at the interface is identified as the probable reason. The uniformity and consistency of film composition is also examined in this chapter. Another salient feature of the process is its capability to coat any complex geometry conformally, allowing the possibility of depositing the material in a way to ―wrap around‖ the three-dimensional inductor structures of RF-CMOS. Integration of nanostructure zinc ferrite thin films onto on-chip spiral inductor structures has been demonstrated successfully. The magnetic-core inductors so obtained exhibit the highest inductance density (700 nH/mm2) and the highest Q factor (~20), reported to date, operate at 5 GHz and above, by far the highest reported to date. An increase in inductance density of as much as 20% was achieved with the use of just 1 µm thick film of zinc ferrite covering only the ―top‖ of the spiral structure, i.e., up to 20% of chip real estate can potentially be freed to provide additional functionality. The microwave-assisted solution-based deposition process described in this thesis is meant for ‗post-CMOS‘ processing, wherein the film deposited on some specific electronic components can add desired functionality to or improve the performance of a component (circuit) underneath. However, the effect of such ‗post-CMOS‘ processing on the active MOS devices, interconnects, and even inter-layer-dielectrics fabricated prior to the deposition has to be mild enough to leave the performance of delicate MOS characteristics intact. Such CMOS-compatibility of the present deposition process has been tested with a satisfactorily positive result.

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