Quarter-wave switched oscillators (SWOs) are an important technology for the generation of high-power, moderate bandwidth (mesoband) wave forms. The use of SWOs in high power microwave sources has been discussed for the past 10 years [1-6], but a detailed discussion of the design of this type of oscillators for particular waveforms has been lacking. In this dissertation I develop a design methodology for a realization of SWOs, also known as MATRIX oscillators in the scientific community.A key element in the design of SWOs is the self-breakdown switch, which is created by a large electric field. In order for the switch to close as expected from the design, it is essential to manage the electrostatic field distribution inside the oscillator during the charging time. This enforces geometric constraints on the shape of the conductors inside MATRIX. At the same time, the electrodynamic operation of MATRIX is dependent on the geometry of the structure. In order to generate a geometry that satisfies both the electrostatic and electrodynamic constraints, a new approach is developed to generate this geometry using the 2-D static solution of the Laplace equation, subject to a particular set of boundary conditions. These boundary conditions are manipulated to generate equipotential lines with specific dimensions that satisfy the electrodynamic constraints. Meanwhile, these equipotential lines naturally support an electrostatic field distribution that meets the requirements for the switch operation.To study the electrodynamic aspects of MATRIX, three different (but interrelated) numerical models are built. Depending on the assumptions made in each model, different information about the electrodynamic properties of the designed SWO are obtained. In addition, the agreement and consistency between the different models, validate and give confidence in the calculated results.Another important aspect of the design process is understanding the relationship between the geometric parameters of MATRIX and the output waveforms. Using the numerical models, the relationship between the dimensions of MATRIX and its calculated resonant parameters are studied. Finally, I present a comprehensive design methodology that generates the geometry of a MATRIX system from the desired specification then calculates the radiated waveform.

International Telemetering Conference Proceedings / October 30-November 02, 1989 / Town & Country Hotel & Convention Center, San Diego, California / During high-power microwave (HPM) testing, where the item under test is subjected to power levels up to several thousand W/cm , the RF energy present will make typical 2 telemetry RF links useless. Therefore, other means must be used to retrieve the data during the tests. One method to accomplish data retrieval is to replace the RF data link with a fiber-optic link. This is done by replacing the transmitter with a fiber-optic transmitter on the sending end and the RF receiver with a fiber-optic receiver on the receiving end. Although this sounds simple, it is not always so. Solutions for PCM and FM-FM systems are relatively straightforward, whereas PAM systems present a unique set of problems. This paper addresses possible solutions for PCM and FM-FM and three possible solutions for PAM, one being by using a PAM-to-PCM converter.

The free electron laser (FEL) is among the latest technologies of interest to the U.S. military, in particular, the Navy. In naval applications, FEL laser would serve as a self-defense weapon system, protecting the ship from an array of threats including anti-surface cruise missiles and small boats. This system's potential range and deep magazine makes it ideal as point defense against incoming missiles. Its inexpensive cost of only a few dollars per engagement and multi-mission capability makes this future weapon system superior to the short-range missile-defense systems employed today. The most powerful FEL is currently located in Jefferson Lab, operating at 10 kW, two orders of magnitude short of the 1 MW power level required for weapons application. This thesis will describe the components and theory of operation of the FEL, as well as analyze two competing designs for the next step in the evolution of the future weapon system, the 100 kW FEL, proposed by Brookhaven and Los Alamos National Labs. Due to advances in NPS simulation techniques for the amplifier configuration, a more in depth analysis including the effects of electron beam tilt and shift is performed for the first time on these proposed designs.

The outstanding features of modular multilevel converters (MMC) have recently gained much attention in the high-voltage direct-current (HVDC) transmission field. Power quality, converter cost and system performance are three crucial aspects of HVDC MMCs which are directly linked to the converter modulation and switching schemes. High power quality and performance require high switching frequency and large cell capacitor whereas low switching frequency and small cell capacitor are needed to reduce the converter cost. The main objective of this thesis is to propose a practical switching method for HVDC MMCs which balances the aforementioned contradictory requirements. A mathematical analysis of the converter switching pattern, against the power quality and converter cost, has been conducted to formulate an optimization problem for MMCs. Different objective functions are studied for the formulated optimization problem such as converter loss minimization, voltage imbalance minimization and computational burden minimization. This thesis proposes three methods to address different objective functions. Ultimately, a real-time simulator has been built to practically verify and investigate the performance of the proposed methods in a realistic point-to-point HVDC link. The most significant outcome of this thesis is the tolerance band-based switching scheme which offers a direct control of the cell capacitor voltage, low power losses, and robust dynamic performance. As a result, the converter switching frequency can reach frequencies as low as 70 Hz (with the proposed cell tolerance band (CTB) method). A modified optimized CTB method is proposed to minimize the converter switching losses and it could reduce the converter switching losses by 60% in comparison to the conventional phase shifted carrier modulation method. It is concluded intelligent utilization of sorting algorithm can enable efficient HVDC station operation by reducing the converter cost. / <p>QC 20160916</p>

No description available.

Energy storage is currently gaining considerable attention due to the current energy crisis and severe air pollution. The development of new and clean forms of energy and related storing devices is in high demanded. Dielectric capacitors, exhibiting high power density, long life and cycling life, are potential candidates for portable devices, transport vehicles and stationary energy resources applications. However, the energy density of dielectric capacitors is relatively low compared to that of traditional batteries, which inhibits their future development. In the current work, three types of dielectrics, namely antiferroelectric samarium-doped BiFeO3 (Bi1-xSmxFeO3), linear dielectric (potential antiferroelectric) BiNbO4 and incipient ferroelectric TiO2, have been investigated to develop their potential as energy storage capacitors. For the samarium-doped BiFeO3 (Bi1-xSmxFeO3) system, the effect of samarium content in the A-site (x=0.15, 0.16, 0.165 and 0.18) on the structural phase transitions and electrical properties across the Morphotropic Phase Boundary (MPB) were studied. A complex coexistence of rhombohedral R3c, orthorhombic Pbam and orthorhombic Pnma was found in the selected compositions. The R3c phase is the structure of pure BiFeO3, the Pbam phase has a PbZrO3-like antiferroelectric structure and the Pnma phase has a SmFeO3-like paraelectric structure. The presence of the PbZrO3-like antiferroelectric structure was confirmed by the observation of the 14{110}, 14{001}, 12{011} and 12{111} superlattice reflections in the transmission electron microscopy diffraction patterns. The weight fractions of the three phases varied with different calcination conditions and Sm substitution level. By increasing the calcination temperature, the weight fractions of the Pbam increased, while that of the R3c decreased. The fraction of the Pnma phase is mainly derived by the Sm concentration and is barely affected by the calcination temperature. The increase of Sm concentration, determined an increase of the weight fraction of the Pnma phase and a decrease of the Pbam and the R3c phases. Temperature dependent dielectric measurements and high temperature XRD of Bi0.85Sm0.15FeO3 revealed several phase transitions. The drastic weight fraction change between the Pbam and the Pnma phase around 200 °C is assumed as the Curie transition of the antiferroelectric Pbam phase. The transition at 575 °C is related to the diminishing of the R3c phase and is suggested as the Curie transition of the ferroelectric R3c phase. The Curie point of the antiferroelectric Pbam phase and the ferroelectric R3c phase in the Bi1-xSmxFeO3 ceramics shifted towards lower temperature with an increase of the Sm concentration. Current peaks were obtained in current-electric field loops in Bi0.85Sm0.15FeO3, which are correlated to domain switching in the R3c phase. The ferroelectric behavior was suppressed in Bi1-xSmxFeO3 (x=0.16, 0.165, 0.18), which is due to the gradually diminished contribution from the R3c phase. The system Bi0.82Sm0.18FeO3 showed the highest energy density of 0.64 J cm-3 (error bar ±0.02). For the BiNbO4 system, single phase α-BiNbO4 (space group Pnna) and β-BiNbO4 (space group P-1) powder and ceramics were produced. The longstanding issue related to the sequence of the temperature-induced phase transitions has been clarified. It is demonstrated that the β phase powder could be converted back to the  phase when annealed in the temperature range 800 °C -1000 °C with certain incubation time. The β to  phase transition is a slow kinetic process because sufficient temperature and time are required for the transition. In bulk ceramics with β phase, this transformation is impeded by inner stress, while it is favored by graphite-induced reducing atmosphere. A high temperature  phase has been revealed and the structure has been resolved. The structure of the  phase is monoclinic with a space group of P21/c. The lattice parameters are: a = 7.7951(1) Å, b = 5.64993(9) Å, c = 7.9048(1) Å,  = 104.691(2) Z=4. The volume is 336.76 (2) Å3. The calculated density is 7.217 g cm-3. The phase relationships among ,  and  phases have been clarified. It was found that the  phase (for both powder and ceramic) transforms into the  phase at 1040 °C on heating, and that the  phase always transforms into the  phase at 1000 °C on cooling. Meanwhile, a reversible first-order  to  phase transition is observed at ca. 1000 °C for both powder and ceramic if no incubation is processed on heating. The electric properties of both α- and - BiNbO4 have been investigated. The breakdown field of both ceramics were too low to observe any possible field-induced transition. As a result, linear P-E loops were obtained in each phase. The energy densities of α- and - BiNbO4 ceramics are 0.03 and 0.04 J cm-3 (error bar ±0.001), respectively. For the TiO2 system, ceramics were produced by conventional sintering and spark plasma sintering (SPS). Compared to conventional sintering, SPS technique produced dense ceramics without using sintering aids and avoided abnormal grain growth. Relaxation behavior related to the oxygen hopping among vacant sites is observed in the temperature range of 200 to 600 °C. TiO2 exhibits ultra-low loss at terahertz frequencies due to the reduced contribution of oxygen vacancies relaxation. TiO2 has a high breakdown field, but still has low polarization. The highest energy density obtained inTiO2 ceramics is 0.3 J cm-3 (error bar ±0.01).

With the increasing interest in offshore wind power, the related technologies, including HVDC networks, are gaining similar levels of attention. For large scale wind farms far from shore, high voltage DC transmission can provide several advantages over traditional high voltage AC transmission. This thesis focuses on DC/DC converters, a core part of the HVDC network, especially for use in the high voltage, high power and offshore wind environment. The thesis examines a wide range of possible DC/DC converter topologies for the application. Different topologies are compared and evaluated in detail for use in a high power situation. Based on these results, three DC/DC converter topologies are selected for more detailed modelling. The simulation processes and results are presented in the thesis, which reveals the limitations and behaviour of the topologies when they are used at the MW level. In addition, the high power semiconductor switching devices are discussed and evaluated for each topology. To assess the suitability of the DC/DC converter topologies in the offshore wind application, the selected converter topologies are also analysed and modelled combined with a PMSG wind turbine. Finally, a down-scaled DC/DC converter prototype is built to verify the analysis and simulation results.

No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, December 1997. / Includes bibliographical references. Also available on the Internet.

Recently, the high-power light-emitting diodes (LEDs) have been used from the traditional indicator purpose to general illumination purpose. The operating environment and requirement has been more severe. The long operating life high efficiency and high reliability are its main feature attracting the lighting community to this technology. The effect of operating temperature on the degradations of high-power blue LEDs is studied in this thesis. The experiment, measurements, and finite element simulations were conducted to investigate the possible causes of LED degradation. The influence of LED material degeneration on the radiometric pattern was analyzed by tracing rays simulation. Different groups of sample LEDs produced by Lumileds, Unity opto technology Co., and Everlight electronics Co. were studied. Different operating ambient temperatures, e.g. 80oC, 100 oC, and 120 oC, were considered in the accelerated aging test. Experimental results indicated that yellowing, carbonization, gel degeneration, lens chapping and deformation were observed during the test. Results also indicated that the operating temperature is the key factor for LED failure mechanism, that is, different operating ambient temperature may lead to different degradation phenomenon. Numerical simulation results shown that the creep caused by high temperature and thermal stress would cause solder takeoff. This takeoff defects were observed in experimental results. Through ray tracing simulation, it is assured that gel degeneration would change the radiometric pattern of the LED significantly.