­^¤åºK­n Electro-optic probing techniques are advancing rapidly in recent years. These techniques have been proven to be an effective tool in parameter extraction of semiconductor devices such as response time, delay time as well as scattering parameters. Not only the magnitude of the electric field but also the direction of the corresponding E-field direction are measured in several developed electro-optic probing system. By incorporated these techniques, the near-field electric field vectors can be estimated and they are valuable information for the analysis of RF circuit devices, e.g., micro-strip transmission line, patch antenna, etc. When probing the 2-D E-field vectors, one can only measure 1-D E-field direction, then rotate the device under test by 90¢X for another orthogonal tangential E-field direction. However the process not only reduces the probing accuracy but also increases the time interval for achieving measurement and lead to obstacles in use. In the thesis, 2D E-field can be obtained without rotating the DUT by using two kinds of modulation schemes, i.e., compressed/stretched deformation modulation(CSDM) and rotational deformation modulation(RDM). These novel techniques provide a total solution for the above bottleneck and improve the sensitivity for different E-field direction. Besides, a heterodyne method is developed to measure the high frequency near-field 2D E-field distribution. By the heterodyne method, the EO probing system can incorporate the CW laser instead of the pulse laser for reducing the cost and enhancing the merits when applied.

This research presents a detection scheme for analyzing the temperature distribution produced by the Joule heating effect nearby the channel wall in a microfluidic chip utilizing a temperature-dependent fluorescence dye. An advanced optical microscope system¡Xtotal internal reflection fluorescence microscope (TIRFM) is used for measuring the temperature distribution on the inner channel wall at the point of electroosmotic flow in an electrokinetically driven microfluidic chip. In order to meet the short working distance of the objective-type TIRFM, microscope cover glass are used to fabricate the microfluidic chips. The short fluorescence excitation depth from a TIRFM makes the intensity information obtained is not sensitive to the channel depth variation which ususally biases the measured results while using conventional epi-fluorescence microscope (Epi-FM). Therefore, a TIRFM can precisely describe the temperature profile of the distance within hundreds of nanometer of the channel wall where consists of the Stern layer and the diffusion layer for an electrokinetic microfluidic system. In order to investigate the temperature distribution produced by the Joule heating effect for electrokinetically driven microchips, this study not only measures the temperature on the microchannel wall by the proposed TIRFM but also measures the temperature inside the microchannel by an Epi-FM. In addition, this research presents a method to reduce the Joule heating effect and enhance the separation efficiency of DNA biosamples in a chip-based capillary electrophoresis (CE) system utilizing pulse DC electric fields. Since the average power consumption is reduced by the pulse electric fields, the Joule heating effect can be significantly reduced. Results indicate the proposed TIRFM method provides higher measurement sensitivity over the Epi-FM method. Significant temperature difference along the channel depth measured by TIRFM and Epi-FM is experimentally observed. In addition, the measured wall temperature distributions can be the boundary conditions for numerical investigation into the Joule heating effect. The proposed method gives a precise temperature profile of microfluidic channels and shows the substantial impact on developing a simulation model for precisely predicting the Joule heating effect in microfluidic chips. Moreover, in the research of reducing the Joule heating effect and enhancing the separation efficiency in a chip-based CE system utilizing pulse electric fields, the experimental and numerical investigations commence by separating a mixed sample comprising two fluoresceins with virtually identical physical properties. The separation level is approximately 2.1 times higher than that achieved using a conventional DC electric field. The performance of the proposed method is further evaluated by separating a DNA sample of Hae III digested £XX¡V174 ladder. Results indicate the separation level of the two neighboring peaks of 5a (271 bp) and 5b (281 bp) in the DNA ladder is as high as 120% which is difficult to be achieved using a conventional CE scheme. The improved separation performance is attributed to a lower Joule heating effect as a result of a lower average power input and the opportunity for heat dissipation during the zero-voltage stage of the pulse cycle. Overall, the results demonstrate a simple and low-cost technique for achieving a high separation performance in CE microchips.

Renewable forms of energy are becoming increasingly important as the world quickly depletes its current energy reserves, and rapidly increases the concentration of pollutants in our environment. Solar technology based on organic semiconductors provides a promising candidate to fulfill a portion of our future energy needs in an environmentally sustainable manner. Organic semiconductors are a collection of pi-conjugated small molecules and polymers which can be implemented in photovoltaic cells that are potentially quite low cost. Currently, however, their commercial applications are limited due to a relatively low efficiency in converting sunlight into usable power. The fundamental physics of such devices must be clarified if these materials are to compete with traditional inorganic solar cells. In this dissertation, two emerging experimental tools are implemented in investigations of the internal electric fields present within operating organic photovoltaic cells. The first set of investigations utilizes the vibrational Stark effect to quantify the electric fields which often form at the interfaces between two organic semiconducting materials. Such interfaces are at the heart of the photocurrent generation process in these devices and any electric fields formed crucially alter device performance. We quantitatively determine the interfacial field present in blends of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) and show that this field depends strongly on annealing conditions. Finally we discuss a correlation between this interfacial electric field, crystalinity and device performance. The second set of investigations take advantage of electric field induced second harmonic generation microscopy to examine the electric potential across active organic solar cells. We again investigate blends of PCBM and P3HT as well as poly(4,4-dioctyldithieno(3,2-b:2',3'-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT) and PCBM. In the former we find that the potential drop across the device shifts dramatically over time under illumination, while in the latter we find a nearly linear drop which remains constant through device operation. We then extend our examinations of PSBTBT:PCBM with EFISH by quantifying the extent of space charge accumulation throughout such devices. / text

The noise in the Langmuir Probe and Plasma Wave Instrument (LP-PWI) on board ESA:s future Jupiter satellite JUICE (Jupiter ICy Moons Explorer) was investigated. Thermal Johnson-Nyquist noise and shot noise, caused by fluctuations in the probe-plasma currents, were combined with the quasi-thermal noise (QTN) due to thermal fluctuations in the electric field in the plasma, using a small signal equivalent circuit model. The contributions and effects of each of the considered noise sources were examined and compared for a number of representative space plasma conditions, including the cold dense plasma of Ganymede's ionosphere and the hot tenuous plasma out in the Jovian magnetosphere. The results showed that in the cold dense plasma of Ganymede's ionosphere, the antenna was long compared to the Debye length and the quasi-thermal noise had a clearly pronounced peak and a steep high-frequency cut-off. For an antenna biased to 1 V with respect to the plasma, the shot noise due to the ambient plasma was the dominant source of noise. For a an antenna at the floating potential the photoelectron shot noise coalesced with the shot and Nyquist noises of the ambient plasma to form almost a single curve. In the hot tenuous plasma out in Jupiter's magnetosphere, the antenna was short compared to the Debye length and the QTN spectrum was much flatter, with little or no peak at the plasma frequency and a very weak high-frequency cut-off. For an antenna biased to 1 V, the shot noise due to photoelectron emission dominated at Callisto's orbital position whereas at Ganymede's and Europa's orbital positions the Nyquist and shot noises of the ambient plasma particles were the dominant noise components. For an antenna at the floating potential, the shot and Nyquist noises of the ambient plasma also dominated the output noise, except at Europa's orbital position, where the quasi-thermal noise was the largest noise component for frequencies at and above the plasma frequency. The numerical calculations were performed using MATLAB. The code was made available in a Git repository at https://github.com/eliasodelstad/irfuproj_JUICE_noise.

This thesis studies the application of a multi-objective niched Pareto genetic algorithm on the design optimization of an electric field mill sensor. The original sensor requires resonant operation. The objective of the algorithm presented is to optimize the geometry eliminating the need for resonant operation which can be difficult to maintain in the presence of an unpredictable changing environment. The algorithm evaluates each design using finite element simulations. A population of sensor designs is evolved towards an optimal Pareto frontier of solutions. Several candidate solutions are selected that offer superior displacement, frequency, and stress concentrations. These designs were modified for fabrication using the PolyMUMPs abrication process but failed to operate due to the process. In order to fabricate the sensors in-house with a silicon-on-glass process, an anodic bonding apparatus has been designed, built, and tested.

No description available.

2012 IEEE International Symposium on Electrical Insulation (ISEI), June 10-13, 2012, Ritz Carlton Hotel, San Juan, PR, USA

The results of a solid-state 11B NMR study of a series of boronic acids, boronic esters, and boronic acid catechol cyclic esters with aromatic substituents are reported in this thesis. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 T and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. It can be concluded that when adequate electronic variation is present in the compounds being studied, Ω is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters. Importantly, these data are only reliably accessible in ultrahigh magnetic fields. The experimental span values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of the dihedral angle, and the type of aromatic ring system present.

This thesis studies the application of a multi-objective niched Pareto genetic algorithm on the design optimization of an electric field mill sensor. The original sensor requires resonant operation. The objective of the algorithm presented is to optimize the geometry eliminating the need for resonant operation which can be difficult to maintain in the presence of an unpredictable changing environment. The algorithm evaluates each design using finite element simulations. A population of sensor designs is evolved towards an optimal Pareto frontier of solutions. Several candidate solutions are selected that offer superior displacement, frequency, and stress concentrations. These designs were modified for fabrication using the PolyMUMPs abrication process but failed to operate due to the process. In order to fabricate the sensors in-house with a silicon-on-glass process, an anodic bonding apparatus has been designed, built, and tested.

Nanofibres have been the subject of recent intensive research due to their unique properties, especially their large surface-area-to-volume ratio, which is about one thousand times higher than that of a human hair. They also have several other remarkable characteristics, such as flexibility in surface functionality, superior mechanical properties such as stiffness and tensile strength, their capacity to be formed into a variety of shapes, and the fact that they can be produced from a wide range of organic and inorganic polymers. These outstanding properties make polymer nanofibres the optimal candidates for providing significant improvement in current technology and for opening the door to novel applications in many research areas. Electrospinning is a straightforward and inexpensive process that produces continuous nanofibres from submicron diameters down to nanometre diameters. Many researchers have successfully electrospun a variety of polymer solutions into nanofibres. However, electrospinning any polymer solution directly is not straightforward or simple because of the number of parameters that influence the electrospinning process. The characteristics of the electrospun jet and the morphology of the resultant fibres are highly dependent on the properties of the polymer solution. In addition, what are favourable processing conditions for one polymer solution may not be suitable for another solution. A literature review revealed that there is no clear understanding of the behaviour of the electrospun jet and the way in which fibre morphology varies with variations in influential parameters. In addition, reported results contain significant inconsistencies and very little research has examined the effects of electrical parameters such as the electric field, the polarity of the electrode, and the conductivity and permittivity of the solution. Furthermore, no research has been conducted with respect to optimizing the electrospinning process. In this thesis, a comprehensive study was carried out by giving a special attention to the effects of electric field that have not been thoroughly investigated in the past. The electric field between the needle tip and the collector plate was altered by varying the applied voltage, distance between the needle tip and the collector plate, the inner diameter of the needle, and polarity of the voltage. Based on the experimental work, it was found that the behavior of Taylor cone, the length of the straight jet portion, and whipping jet region is highly influenced by the distribution of the electric field between the needle tip and the collector plate. Based on the stability of the Taylor cone, it was concluded that the stable operating region of the electrospun jet is a very narrow region and it is between 0.9 – 1.1kV/mm for the range of experiments that were carried out in this study. The length of the straight jet portion of the electrospun jet shows a linear relationship to the applied electric field at the tip of the fluid droplet and the whipping jet region is influenced by both the electric field at the tip of the fluid droplet and the distance between the needle and the collector plate. A confirmation were made that there must be enough distance between the needle tip and the collector plate (>200mm) to operate over the complete range of voltages without affecting drying of nanofibres. It was also concluded that the morphology and diameter of the collected nanofibres depend significantly on both the length of the straight jet portion and size of the whipping region. The effects of polarity of the applied voltage on the electrospinning process and nanofibre morphology were investigated using the positive, negative, and AC voltages. However, it was found that the electrospinning can not be achieved with the application of 60Hz AC voltage. It was observed that the behavior of Taylor cone, the straight jet portion, and the whipping jet region depend on the polarity of the applied voltage. During the study, it was accomplished that the reason for this different behavior is the disparity of ionization in the polymer solution with the application of positive and negative high voltages. In this thesis, the effects of multi-needle arrangements on the electrospinning process and fibre morphology were also explained. Finite element method (FEM) simulation results revealed that the local electric field strength around each needle tip weakens significantly in the case of multi-needle schemes due to the mutual influence of other needles in the arrangement compared to the single-needle system. The spacing between the needles was varied, and the effects of the needle spacing were examined. The experimental and simulation results were concealed the correlation between the degree of field distortion and the variation in the measured vertical angle of the straight jet portion for different needle spacing. It was concluded that the local field deterioration at the needle tips in multi-needle schemes degrades the electrospinning process significantly and produces considerable variation in the fibre morphology even though the influence of needle spacing on the average jet current and the fibre diameter are not very significant. In this work, the effects of conductivity and ionic carriers on the process of electrospinning and hence on the morphology of nanofibres were studied using polyethylene oxide (PEO) and polyacrylic acid (PAA) aqueous solutions. Different salts including lithium chloride (LiCl), sodium chloride (NaCl), sodium fluoride (NaF), sodium bicarbonate (NaHCO3), potassium chloride (KCl), and cesium chloride (CsCl) were added in different concentrations to the polymer solutions for introducing different ionic carriers into the solution. The results showed that the average fiber diameter decreases with increase in the conductivity of the solution. In addition, it was discovered that the formation of Taylor cone highly depends on the conductivity in the polymer solution. Formation of multi-jets at the fluid droplet when the conductivity of the polymer solution is increased during the electrospinning was also observed. These behaviors were completely explained using the distribution of the surface charge around the electrospun jet and the variation in the tangential electric field along the surface of the fluid droplet. The stretching of the polymer jet can be related to the amount of ionic carries and the size and mobility of positive and negative ions. The increasing amount of ionic carriers and smaller size positive ions enhance the stretching of the electrospun jet. In contrast, the lesser diameter negative ions decrease the stretching of the electrospun jet. The morphology of electrospun nanofibres can also be varied by altering the type of ionic carriers. A charge modifier, which is a container that is used to hold a solvent surrounding the needle tip during the electrospinning, was introduced to facilitate the electrospinning of insulating and high conductivity polymer solutions. The co-axial flow of the filled solvent on the outer surface of the polymer solution helps to induce enough surface charges during electrospinning and it also keeps the electric field tangential to the fluid surface during the process. Therefore, the introduction of charge modifier greatly enhanced the electrospinning behavior of highly insulating and conductive polymer solutions and liquids. The developed charge modifier method was verified by using sodium alginate which is a biopolymer that cannot electrospin alone due to its high electrical conductivity and silicone rubber which is an insulating liquid polymer at room temperature. One of the most commonly used theoretical model of the electrospinning process was modified to incorporate the non-uniform characteristics of the electric field at the tip of the needle. The non-uniform electric field between the needle tip (spinneret) and the collector plate was calculated based on the charge simulation technique (CST). It gives a better representation of the true electrospinning environment compared to the uniform field calculation in the existing model. In addition, a localized approximation was used to calculate the bending electric force acting on the electrospinning jet segments. It was also introduced a constant velocity to initiate the electrospinning jet during simulation. The incorporated modifications gave better results that closely match with the real electrospinning jet. The modified electrospinning model was used to understand the effects of parameters on the electrospinning process and fibre morphology.