Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 90). Also available in electronic version.

Proefschrift Universiteit Maastricht. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

In Electrical Impedance Tomography the conductivity of an object is estimated from boundary measurements. An array of electrodes is attached to the surface of the object and current stimuli are applied via these electrodes. The resulting volt ages are measured. The process of estimating the conductivity as a function of space inside the object from voltage measurements at the surface is called reconstruction. Mathematically the ElT reconstruction is a non linear inverse problem, the stable solution of which requires regularisation nwthods. Most common regularisation methods impose that the reconstructed image should be smooth. Such methods confer stability to the reconstruction process, but limit the capability of describing sharp variations in the sought parameter. In this thesis two new methods of regularisation are proposed. The first method, Gallssian anisotropic regularisation, enhances the reconstruction of sharp conductivity changes occurring at the interface between a contrasting object and the background. As such changes are step changes, reconstruction with traditional smoothing regularisation techniques is unsatisfactory. The Gaussian anisotropic filtering works by incorporating prior structural information. The approximate knowledge of the shapes of contrasts allows us to relax the smoothness in the direction normal to the expected boundary. The construction of Gaussian regularisation filters that express such directional properties on the basis of the structural information is discussed, and the results of numerical experiments are analysed. The method gives good results when the actual conductivity distribution is in accordance with the prior information. When the conductivity distribution violates the prior information the method is still capable of properly locating the regions of contrast. The second part of the thesis is concerned with regularisation via the total variation functional. This functional allows the reconstruction of discontinuous parameters. The properties of the functional are briefly introduced, and an application in inverse problems in image denoising is shown. As the functional is non-differentiable, numerical difficulties are encountered in its use. The aim is therefore to propose an efficient numerical implementation for application in ElT. Several well known optimisation methods arc analysed, as possible candidates, by theoretical considerations and by numerical experiments. Such methods are shown to be inefficient. The application of recent optimisation methods called primal- dual interior point methods is analysed be theoretical considerations and by numerical experiments, and an efficient and stable algorithm is developed. Numerical experiments demonstrate the capability of the algorithm in reconstructing sharp conductivity profiles.

The impedance realizing ability of minimal two-element kind networks is considered. As a preamble, a comprehensive survey of relevant mathematics and existing results is presented. An argument based on group theory is used to demonstrate the complex nature of the solution for non-canonic networks. The modal matrix of normal co-ordinate transformation on the cut set admittance matrix is interpreted geometrically as a set of vectors satisfying certain conditions, imposed by the topology and the parameters of the input function of the network, in two Euclidean vector spaces. The existence of the modal matrix, hence the existence of these vectors, is the necessary and sufficient condition for physical realizability. Explicit formulas are developed for third order networks and numerical algorithms for the fourth order networks. A necessary condition is given on the parameters of Z(s) for realizability for networks containing a linear tree of one kind of element. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The impedances of cables are some of the parameters needed for various studies in cable systems. In this work, the impedances of cables are calculated using the subdivisions of the conductors (including ground) in the system. Use is also made of analytically derived ground return formulae to speed up the calculations. The impedances of most linear materials are calculated with a good degree of accuracy but materials with highly nonlinear properties, like steel pipes, give large deviations in the results when they are represented by the linear model used. The method is used to study a test case of induced sheath currents in bonded sheaths and it gives very good results when compared with the measured values. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Unknown

The purpose of this research is to explore and investigate the biophysical properties of living cells using microfluidics based electrical impedance sensing (EIS) technique. It provides a non-invasive approach to detect label-free biological markers in the regulation of cellular activities even at a molecular level. We specifically focus on the development, testing, and theoretical modeling of electrical impedance spectroscopy for neuroblastoma cells and endothelial cells. First, we demonstrate that the EIS technique can be used to monitor the progressive mitochondrial fission/fusion modification in genetically modified human neuroblastoma cell lines. Our results characterize quantitatively the abnormal mitochondrial dynamics through the variations in cytoplasm conductivity. Secondly, we employ a real time EIS method to determine the biophysical properties of the junctions which join one endothelial cell with one another in a monolayer of endothelial cells. In particular, we examine the role of the protein, c-MYC oncogene, in the barrier function. Our results show that the downregulation of c-MYC oncogene enhances the endothelial barrier dysfunction associated with inflammation. Finally, we measure and find that the electrical admittance (the reciprocal of the impedance) of the monolayer of endothelial cellular networks exhibits an anomalous power law of the form, Y ∝ ωα, over a wide range of frequency, with the value of the exponent, α, depending on the severity of the inflammation. We attribute the power law to the changes of the intercellular electric permeability between neighboring endothelial cells. Thus, the inflammation gives rise to relatively smaller values of α compared to that of the no-inflammation group. Furthermore, we propose a simple percolation model of a large R-C network to confirm the emergent of power law scaling behavior of the complex admittance, suggesting that the endothelial network behaves as a complex microstructural network and its electrical properties may be simulated by a large R-C network. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

In an ideal world, unwanted or undesirable effects in a system could and would be completely ignored. In fact, this was the case in mid-80s' PC design when an 80286 microprocessor running at a "blazing" 12 MHz was considered leading-edge technology. As technology continued to push the envelope and ever-faster designs were realized, more demanding software packages were developed and utilized efficiently. These increasingly sophisticated software packages in turn allowed designers of all disciplines to test systems of escalating complexity. These more complex models placed a heavier burden on the hardware, prompting a push for better and faster hardware designs. The cycle repeats to this day. As such, we are now in an environment where a 1 GHz microprocessor is considered somewhat dated. More importantly, whereas a small 1 nH (1 billionth of a Henry) inductance in a power delivery path was considered inconsequential a decade ago, it is now a barrier to implementing a design. Similarly, the equivalent series inductance (ESL) of a capacitor plays an increasing (and detrimental) role in the behavior and design of today's VRM (Voltage Regulator Module) design. In fact, it is the ESL of the capacitor that hinders proper voltage regulation at high frequencies by increasing the output impedance beyond a desired level. This dilemma has been recognized and several topologies have been proposed to overcome this problem. One category is improved passive devices, with the latest involving array capacitors to achieve near-zero ESL. As passive devices are almost always preferable to active solutions due to their lower losses, these technologies hold great promise, though they are inherently limited in small-footprint applications. A second category is the addition of active devices, which involves the use of some filtering technique to inject or absorb current during a fast transient by the use of semiconductor switches connected to a power source. These switching-state topologies have been shown to be prone to unstable oscillations, often caused by over-reactions or over-corrections of one transient prompting the opposite switch to engage its power source. The research goal is to develop a methodology to use active filters to more-seamlessly extend the control bandwidth of today's VRM technology. A hybrid active power filter is developed which uses bipolar junction transistors (BJT) in the forward-active region to connect a power supply source to the microprocessor. In this way, the switches are used in a way analogous to a dimmer switch (vs. simply 'on' or 'off'). By proper design of the compensator in the feedback loop, the active power filter can be used to suppress transients in any desired frequency range, limited only by the amplifier's current rating and bandwidth. The compensator design's derivation shows the relationship to the output impedance of the active filter. In essence, we are 'designing' a capacitor with a very low ESL, having more desirable output impedance vs. frequency relationship than either a capacitor, or a more complicated VRM with an extended bandwidth. Using this design, however, at very high frequencies (i.e., approaching 1 GHz, or one trillion cycles per second) requires state-of-the-art packaging designs to limit unwanted impedances, and also an ultra-wide GHz bandwidth, high-current operational amplifier. Both of these barriers are outside the scope of this research. As is often the case in research efforts, we have not '˜solved' the problem, but have shifted it to a frequency range where the effect isn't problematic. Experimental results show the use of a hybrid power filter with a VRM with Adaptive Voltage Positioning (AVP) can significantly suppress voltage undershoot during fast transient load current changes. In addition, the design is modified to reduce and possibly eliminate bulk output capacitors. This provides a promising alternative to a Voltage Regulator Module with a very high control bandwidth. Lastly, simulations give an estimate of the required IC design to use an APF to augment packaging capacitors. / Master of Science

No description available.

No description available.