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Impedance Response (impedance + response)
Selected AbstractsInterpreting Impedance Response of Silicon Carbide Whisker/Alumina Composites Through Microstructural SimulationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006David S. Mebane A three-dimensional, object-defined Monte Carlo simulation is applied to alumina-silicon carbide whisker ceramic matrix composites. The simulation takes whisker orientation and size distributions into account simultaneously, and calculates a connectivity factor that relates whisker conductivity to macroscopic conductivity. Simulation results are compared with electrical measurements taken on real samples via impedance spectroscopy. Results show that the effect of whisker clumping can be seen in the impedance response as a decrease in the overall measured conductivity. Results also show that interfacial resistance influences the overall resistivity strongly relative to connectivity at volume fractions far above the percolation threshold. The possible mechanisms for interfacial resistance in the composite and their effect on the impedance response are discussed. [source] On Selection of the Perturbation Amplitude Required to Avoid Nonlinear Effects in Impedance MeasurementsISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Bryan Hirschorn Numerical simulations of electrochemical systems were used to explore the influence of large-amplitude potential perturbations on the measured impedance response. The amplitude of the input potential perturbation used for impedance measurements, normally fixed at a value of 10 mV for all systems, should instead be adjusted for each experimental system. Guidelines are developed for selection of appropriate perturbation amplitudes. A characteristic transition frequency is defined that can be used to tailor a frequency-dependent input signal to optimize signal-to-noise levels while maintaining a linear response. [source] Interpreting Impedance Response of Silicon Carbide Whisker/Alumina Composites Through Microstructural SimulationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006David S. Mebane A three-dimensional, object-defined Monte Carlo simulation is applied to alumina-silicon carbide whisker ceramic matrix composites. The simulation takes whisker orientation and size distributions into account simultaneously, and calculates a connectivity factor that relates whisker conductivity to macroscopic conductivity. Simulation results are compared with electrical measurements taken on real samples via impedance spectroscopy. Results show that the effect of whisker clumping can be seen in the impedance response as a decrease in the overall measured conductivity. Results also show that interfacial resistance influences the overall resistivity strongly relative to connectivity at volume fractions far above the percolation threshold. The possible mechanisms for interfacial resistance in the composite and their effect on the impedance response are discussed. [source] New low profile cavity-backed Hilbert slot antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2006Guido Biffi Gentili Abstract In this paper, the use of a cavity-backed Hilbert surface as an efficient slot-like narrowband radiating aperture is suggested, to exploit its own unique electromagnetic characteristics in the context of radio frequency identification (RFID) applications. The proposed meta-slot antenna (MSA) consists of a Hilbert surface window (HSW) made of a cascade of space-filling slot inclusions of order three and backed by a very shallow cavity that contributes to its surface impedance and radiation characteristics. A straight longitudinal microstrip line printed on a thin, low permittivity substrate, whose ground plane includes the HSW, feeds the aperture through distributed electromagnetic coupling. As illustrated by simulation results and measurements, the antenna behaves as a magnetic current sheet over a ground plane, with a highly frequency-selective impedance response and unidirectional radiation pattern. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2577,2581, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21995 [source] Respiratory impedance response to a deep inhalation in children with history of cough or asthmaPEDIATRIC PULMONOLOGY, Issue 6 2002François Marchal MD Abstract The aim of this study was to describe the change in respiratory impedance induced by a deep inhalation (DI) in children who developed a positive response to inhalation of methacholine (Mch). Eighteen children aged 4.5,12.5 years, presenting with chronic cough or doctor-diagnosed asthma, were studied at baseline after inhalation of Mch and after inhalation of a bronchodilator. Respiratory resistance (Rrs) and reactance (Xrs) were measured by the forced oscillation technique, varying transrespiratory pressure at 12 Hz around the head. The tidal flow (V,) and volume (V) dependence of Rrs before and after the DI was characterized according to the equation Rrs,=,K1,+,K2,·,|V,|,+,K3,·,V. DI induced no significant change at baseline or after inhalation of a bonchodilator. During Mch challenge, Rrs and K1 were significantly lower, and K3 and Xrs significantly less negative after DI than before, during both inspiration and expiration; there was no change in K2. We conclude that DI results in a decrease in Rrs in children with induced bronchoconstriction. The associated changes in Xrs, K1, and K3, and lack of decrease in K2, suggest that dilatation of airways occurs at the bronchial level, with little contribution of the upper airways or of a change in breathing patterns. Pediatr Pulmonol. 2002; 33:411,418. © 2002 Wiley-Liss, Inc. [source] Planar aqueous electrode technique for polymer impedance spectroscopyPOLYMER ENGINEERING & SCIENCE, Issue 3 2009T. Bai In this article, we develop an aqueous electrode technique that can adapt to complex sample geometries while maintaining perfect contact between the electrodes and the measured sample. In contrast to surface deposited electrodes, the aqueous electrode technique measures the ionic conduction of the polymer sample instead of the inherent dielectric properties of the polymer. Polymer ionic conduction is often related to the polymer thermodynamic state, which itself is closely linked to many other polymer properties. As such, the aqueous electrode method provides an approach to conduct in situ monitoring of polymer samples subjected to degradation; changes in the impedance provide an indication of polymer sample degradation. This article presents the aqueous electrode setup and discusses experimental results obtained using it. Changes in the impedance response of PVC and polyimide films due to moisture absorption, ionic conduction, pinholes, chemical degradation, and temperature are presented. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] |