The ceramic composite system containing Al₂O₃ and SiCw has seen multiple uses depending on its processing method. Both the thermomechanical properties and the electrical properties have piqued the interest for potential commercial applications. These include cutting tool inserts and microwave heating elements. Composite samples made by extrusion were pressureless sintered and characterized as a function of frequency, bias, sample length, and whisker orientation. Dry pressed percolated specimens containing different amounts of sintering aids were hot pressed and spark plasma sintered. The microstructure and electrical properties were compared.

This System-on-Chip implementation is aimed at measuring small impedance with high accuracy. This system consists of an Analog sensor, Analog to Digital converter and a computational unit that is used to calculate the magnitude and phase of the impedance. The SoC can find its application in affinity based biosensors that use impedance spectroscopy to determine the properties of the analyte. Other applications include measuring impedances from probes buried in building structures to monitor the health of he buildings. / text

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: impedance spectroscopy; non-invasive instrumentation; ischemia. Includes bibliographical references (p. 146-149).

Impedance spectroscopy (IS) is an important technique for monitoring and detection of biomaterials. In order to enable point-of-care systems, low-cost IS systems capable of rapidly measuring a wide range of biomaterials are required. This thesis presents two IS systems, one in Printed Circuit Board level and the other in Integrated Circuit level. The board level system is built for preliminary experimental data collection; it is capable of measuring impedance from 1KHz to 100KHz with 200mV signal injection into cell sample. Experimental results show that magnitude and phase error are less than 6.6% and 2.2%, respectively. An IC level IS front-end is also proposed which utilizes a time-to-digital converter (TDC) and a peak detector circuit (PDC) for quick measurement of both impedance phase and magnitude, respectively. Designed in a 0.18μm CMOS process, the front-end is capable of performing impedance measurements in 6μs at frequencies ranging from 100Hz-10MHz and with a 100Ω-1MΩ dynamic range. Simulation results with cell impedance models show that the system achieves <2.5% magnitude and <2.2 degree phase error. The front-end consumes 28mW total power and occupies 0.4mm^2 area.

No description available.

Impedance spectroscopy (IS) was used to evaluate the microstructural changes of a thermally-grown oxide (TGO) layer on a nickel-based superalloy or bond coat, with or without a thermal barrier coating (TBC) system, at various temperatures. TBC is used for hot section parts of gas turbine engine, such as turbine blades and vanes. However, spallation of TBC can take place due to long-term operation at high temperature. The spallation is mainly caused by both microstructural changes and thermal stresses as a result of oxide layer (mainly alumina) formation and growth at the interface between the TBC and bond coat. The electrical resistance and capacitance of the oxide layer, formed from oxidation of IN738LC superalloy at high temperature, were obtained from fitting the results of the measured impedance diagrams based on an equivalent circuit model. The equivalent circuit model should represent the features of the oxide layer or the TBC system. The electrical resistance of the oxide layer increased with increasing oxidation time for samples exposed to air at 900°C. Similar results were obtained for the NiCrCoAIY bond coat samples and the TBC systems. The capacitance decreased with increasing thickness of the alumina layer. The activation energy of electrical conduction was used to characterise the alumina layer formed on the bond coat at 900°C, 1000°C and 1100°C. The activation energy values for the alumina layer, formed at various temperatures, decrease with increasing impurity or porosity. Changes in the electrical properties of TGOs are correlated with those in their microstructure and microchemistry. The degradation of a TBC can be identified, when the electrical resistance of the TGO decreases with increasing oxidation time. The fast decrease in resistivity corresponds to the compositional change in the TGO from cc-Al2O3 to a mixture of a-Cr2O3 and (Ni or Co)(Cr or Al)2O4 spinel. The disappearance of a-A1203 in the TGO makes the scale non-protective and leads to cracks and spallation of TBCs. Non-destructive testing of the crack formation in a TBC system is essential for predicting the failure and lifetime of TBCs in service. IS was used to evaluate the crack formation in the TBC system due to thermal cycling. During the thermal cycling, cracks initiated and propagated along the interface between the TGO and the yttrium stabilised zirconia (YSZ), used as a TBC. This caused the spallation of the TBC eventually. The propagation of cracks at the interface of TGO/YSZ was found to contribute to an increase in the interfacial impedance. The interfacial area determines the interfacial resistance corresponding to the oxygen reaction. Therefore, the crack propagation induced an increase of the interfacial resistance, whereas the interfacial capacitance showed no trend in its alteration with the propagation of the cracks. As a result, the relaxation frequency of the interface moved towards a lower frequency during the propagation of the cracks. Therefore, impedance spectroscopy has been used to examine the crack formation in TBC system non-destructively. By using scanning electron microscopy and X-ray diffraction techniques, the composition and microstructure of the oxide scales were examined. It was found that their electrical properties were determined, not only by the microstructure of the oxide scales, but also by the composition of the oxide scales. By determining the relationship between the electrical properties, microstructure and composition of the oxide scales, IS could be used as a non-destructive technique for monitoring the oxidation of metallic alloys at high temperature in gas turbine engine components.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leave 112-117) Also available in print.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 87-88).

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

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