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We developed a quantitative measurement technique using atomic force microscopy (AFM) to study the effects of both DC and AC external electric fields on the forces between two dielectric microspheres. In this work we measured the DC and AC electric field-induced forces and adhesion force between two barium titanate (BaTiO?) glass microspheres in a low humidity environment by this technique. The objective here is to find out the correlation between these measured forces and applied field strength, frequency, and the separation distance between the two spheres was studied. Since the spheres would oscillate under an AC field, the AC field-induced force was divided into dynamic component (i.e., time-varying term) and static component (i.e., time-averaged term) to investigate. The oscillatory response occurs at a frequency that is twice the drive frequency since the field-induced force is theoretically proportional to the square of the applied field. This behavior can be observed in the fast Fourier transformation (FFT) spectra of the time series of the deflection signal. The magnitude of the vibration response increases when the frequency of the drive force is near resonant frequency of the particle-cantilever probe. The amplitude of this vibration increases with proximity of the two particles, and ultimately causes the particles to repeatedly hit each other as in tapping mode AFM. The effect of the Maxwell-Wagner interfacial relaxation on the DC electric field-induced force was discovered by monitoring the variation of the field-induced force with time. The static component of the AC electric field-induced force does not vary with the applied frequency in the range from 1 to 100 kHz, suggesting that the crossover frequency may equal to or less than 1 kHz and the permittivities of the BaTiO? glass microspheres and medium dominate the field-3 induced force. The AC field-induced force is proportional to the square of the applied electric field strength. This relationship persists even when the separation between the spheres is much smaller than the diameter of the microspheres. The large magnitude of the force at small separations suggests that the local field is distorted by the presence of a second particle, and the continued dependence on the square of the field but the measured force is much larger than the theoretical results, suggesting that the local electric field around the closely spaced spheres is distorted and enhanced but the effects of the local field distortion may have not much to with the applied electric field. Compared with the calculated results from different models, our results demonstrate that the field-induced force is much more long-range than expected in theory. In addition, the DC field-induced adhesion force is larger than the AC field-induced one due to the interfacial charge accumulation, agreeing with the discovery of the Maxwell-Wagner interfacial relaxation effect on the DC field-induced force. No obvious correlation between the field-induced adhesion and the applied frequency is found. However, both the DC and AC field-induced adhesion forces display the linearity with the square of the applied electric field strength as well. / Master of Science

Microwave processing presents a relatively new heating source for a large variety of processes and materials. Depositing microwave energy volumetrically, microwave heating appears as a good alternative for sintering ceramics by decreasing the process time, offering better energy efficiency, but also diminishing thermal gradients inside the materials, producing more uniform heating, and therefore better mechanical properties. However, the strong temperature dependence of the ability to store or absorb the microwave energy of the material, and its variation of several orders of magnitude when the temperature increases, makes the control of the temperature of the material problematic and can lead to thermal runaway. The research reported in this thesis uses numerical modeling to investigate the feasibility of temperature control for continuous microwave processing of thermal runaway materials, applied specifically to alumina and zirconia fibers. Using a one-dimensional model valid for any continuous material moving through a microwave cavity, we were able to demonstrate control of the temperature inside the fiber by using a new approach of controlling the distribution of the energy deposited along the fiber. We were able to determine an electric field strength profile to generate the desired temperature profile for both fibers. / Master of Science

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / During biodiesel production, crude biodiesel and glycerin are separated in resting tanks due to gravity and differences in density, glycerin accumulates at the base of the contender; such operation is called decantation. The decantation stage, within the production of biodiesel based on recycled oil, takes from 8 to 24 h to complete. Therefore, the development of an automatic biodiesel decanting system is presented in order to optimize the production time in the line of this bio-fuel. The process consists of applying an electric field through two electrodes at 9 kV and simultaneously applying temperature. The results of the implementation showed that the production time was reduced by up to 99% without affecting the quality of biodiesel, according to the parameters of the American Society for Testing and Materials (ASTM). / Revisión por pares

To achieve higher power density, converters and components must be able to handle higher voltage and current ratings at higher percentages of efficiency while also maintaining low cost and a compact footprint. To meet such demands, medium-voltage resonant converters have been favored by researchers for their ability to operate at higher switching frequencies. High frequency (HF) operation enables soft switching which, when achieved, reduces switching losses via either zero voltage switching (ZVS) or zero current switching (ZCS) depending on the converter topology. In addition to lower switching losses, the converter operates with low harmonic waveforms which produce less EMI compared to their hard switching counterparts. Finally, these resonant converters can be more compact because higher switching frequencies imply decreased volume of passive components. The passive component which benefits the most from this increased switching frequency is the transformer. The objective of this work is to design a >400 kHz, 100 kW transformer which will provide galvanic isolation in a Solid-State Transformer (SST) based PEBBs while maintaining high efficiency, high power density, and reduced size. This work aims to present a simplified design process for high frequency transformers, highlighting the trade-offs between co-dependent resonant converter and transformer parameters and how to balance them during the design process. This work will also demonstrate a novel high frequency transformer insulation design to achieve a partial discharge inception voltage (PDIV) of >10 kV. / Master of Science / As the world's population expands and countries progress, the demand for electricity that is high-powered, highly efficient, and dependable has increased exponentially. Further, it is integral to the longevity of global life that this development occurs in a fashion that mitigates environmental consequences. The power and technology sectors have been challenged to address the state of global environmental affairs, specifically regarding climate change, carbon dioxide emissions, and resource depletion. To move away from carbon emitting, non-renewable energy sources and processes, renewable energy sources and electric power systems must be integrated into the power grid. However, the challenge lies in the fact that there is not an easy way to interface between these renewable sources and the existing power grid. Such challenges have undermined the widespread adoption of renewable energy systems that are needed to address environmental issues in a timely manner. Recent developments in power electronics have enabled the practical application of the solid-state transformer (SST). The SST aims to replace the current, widespread form of power transformation: the line frequency transformer (50/60 Hz). This transformer is bulky, expensive, and requires a significant amount of additional circuitry to interface with renewable energy sources and electric power systems. The SST overcomes these drawbacks through high frequency operation (>200 kHz) which enables higher power at a reduced size by capitalizing on the indirect proportionality between the two parameters. The realization of the SST and its implementation has the ability to greatly advance the electrification of the transportation industry which is a top contributor to carbon emissions. This work aims to demonstrate a >400 kHz, 100 kW SST with a novel magnetic design and insulation structure suited for electric ship applications.

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This thesis aims to determine the distribution of the relative permittivity for random mixtures of material using electromagnetic simulations. The algorithm used in the simulations is the FDTD method which solves Maxwell's equations numerically in the time-domain. The material is modeled as randomly shaped particles with radius 12 ± 10 micrometre in x- and y-direction and radius 3 ± 1 micrometre in zdirection. The scattering parameters from the transmitted and reflected electric field when a plane wave interacts with the material are measured. The relative permittivity is determined from the scattering parameters using the iterative Baker-Jarvis method. The simulations shows that both the distribution and the value of the relative permittivity is low when the particles have non conducting layers to force interruptions to prevent percolation, a conducting path between the particles. The most important result is of the kind where the simulations do not have any boundaries to prevent percolation. These simulations reflects how the relative permittivity distributes in real measurements. It is established that the value of the relative permittivity has a large distribution and also that percolation occurs because of the periodic structures.

The application of a theoretical framework for calculating the radial electric field in the DIII-D tokamak edge plasma is discussed. Changes in the radial electric field are correlated with changes in many important edge plasma phenomena, including rotation, the L-H transition, and ELM suppression. A self-consistent model for the radial electric field may therefore suggest a means of controlling other important parameters in the edge plasma. Implementing a methodology for calculating the radial electric field can be difficult due to its complex interrelationships with ion losses, rotation, radial ion fluxes, and momentum transport. The radial electric field enters the calculations for ion orbit loss. This ion orbit loss, in turn, affects the radial ion flux both directly and indirectly through return currents, which have been shown theoretically to torque the edge plasma causing rotation. The edge rotation generates a motional radial electric field, which can influence both the edge pedestal structure and additional ion orbit losses. In conjunction with validating the analytical modified Ohm’s Law model for calculating the radial electric field, modeling efforts presented in this dissertation focus on improving calculations of ion orbit losses and x-loss into the divertor region, as well as the formulation of models for fast beam ion orbit losses and the fraction of lost particles that return to the confined plasma. After rigorous implementation of the ion orbit loss model and related mechanisms into fluid equations, efforts are shifted to calculate effects from rotation on the radial electric field calculation and compared to DIII-D experimental measurements and computationally simulated plasmas. This calculation of the radial electric field will provide a basis for future modeling of a fast, predictive calculation to characterize future tokamaks like ITER.

<p>Electroporation is a biological cell's natural reaction to strong electric fields, where transient pores are created in the cell membrane. While electroporation holds promise of being a safe and effective tool for enhancing molecular delivery in numerous medical applications, it remains largely confined to preclinical research and clinical trials due to an incomplete understanding of the exact mechanisms involved. Muscle fibers are an important delivery target, but traditional theoretical studies of electroporation ignore the individual fiber geometry, making it impossible to study the unique transverse and longitudinal effects from the pulse stimulus. In these long, thin muscle fibers, the total reaction of the fiber to the electric field is due to fundamentally different effects from the constituent longitudinal and transverse components of the electric field generated by the pulse stimulus. While effects from the transverse component have been studied to some degree, the effects from the longitudinal component have not been considered. </p><p>This study develops a model of electroporation and delivery of small molecules in muscle tissue that includes effects from both the transverse and longitudinal components of the electric field. First, an asymptotic model of electric potential in an individual muscle fiber is derived that separates the full 3D boundary value problem into transverse and a longitudinal problems. The transverse and longitudinal problems each have their own respective source functions: the new "transverse activating function" and the well known longitudinal activating function (AF). This separation enhances analysis of the different effects from these two AFs and drastically reduces computational intensity. Electroporation is added to the asymptotic fiber model, and simplified two-compartment mass transport equations are derived from the full 3D conservation of mass equations to allow simulation of molecular uptake due to diffusion and the electric field. Special emphasis is placed on choosing model geometry, electrical, and pulsing parameters that are in accordance with experiments that study electroporation-mediated delivery of small molecules in the skeletal muscle of small mammals.</p><p>Simulations reveal that for fibers close to the electrodes the transverse AF dominates, but for fibers far from the electrodes the longitudinal AF enhances uptake by as much as 2000%. However, on the macroscopic tissue level, the increase in uptake from the longitudinal AF is no more than 10%, given that fibers far from the electrodes contribute so little to the total uptake in the tissue. The mechanism underlying the smaller effect from the longitudinal AF is found to be unique to the process of electroporation itself. Electroporation occurs on the short time scale of polarization via the transverse AF, drastically increases membrane conductance, and effectively precludes further creation of pores from charging of the membrane via the longitudinal AF. The exact value of enhancement in uptake from the longitudinal AF is shown to depend on pulsing, membrane, and tissue parameters. Finally, simulation results reproduce qualitative, and in some cases quantitative, behavior of uptake observed in experiments.</p><p>Overall, percent increase in total tissue uptake from the longitudinal AF is on the order of experimental variability, and this study corroborates previous theoretical models that neglect the effects from the longitudinal AF. However, previous models neglect the longitudinal AF without explanation, while the asymptotic fiber model is able to detail the mechanisms involved. Mechanisms revealed by the model offer insight into interpreting experimental results and increasing efficiency of delivery protocols. The model also rigorously derives a new transverse AF based on individual fiber geometry, which affects the spatial distribution of uptake in tissue differently than predicting uptake based on the magnitude of the electric field, as used in many published models. Results of this study are strictly valid for transport of small molecules through small non-growing pores. For gene therapy applications the model must be extended to transport of large DNA molecules through large pores, which may alter the importance of the longitudinal AF. In broader terms, the asymptotic model also provides a new, computationally efficient tool that may be used in studying the effect of transverse and longitudinal components of the field for other types of membrane dynamics in muscle and nerves.</p> / Dissertation