Thesis (M.S. in mechanical engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 11, 2010). "Department of School of Engineering and Computer Science, Vancouver." Includes bibliographical references (p. 58-59).

No description available.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 129-136).

No description available.

There is a current trend towards the use of wearable biomedical devices for the purpose of recording various biosignals, such as electrocardiograms (ECG). Wearable devices have different issues and challenges compared to nonwearable ones, including motion artifacts and contact characteristics related to body-conforming materials. Due to this susceptibility to noise and artifacts, signals acquired from wearable devices may lead to incorrect interpretations, including false alarms and misdiagnoses. This research addresses two challenges of wearable devices. First, it investigates the effect of applied pressure on biopotential electrodes that are in contact with the skin. The pressure affects skin–electrode impedance, which impacts the quality of the acquired signal. We propose a setup for measuring skin–electrode impedance during a sequence of applied calibrated pressures. The Cole–Cole impedance model is utilized to model the skin–electrode interface. Model parameters are extracted and compared in each state of measurement with respect to the amount of pressure applied. The results indicate that there is a large change in the magnitude of skin–electrode impedance when the pressure is applied for the first time, and slight changes in impedance are observed with successive application and release of pressure. Second, this research assesses the quality of ECG signals to reduce issues related to poor-quality signals, such as false alarms. We design an algorithm based on Deep Belief Networks (DBN) to distinguish clean from contaminated ECGs and validate it by applying real clean ECG signals taken from the MIT-BIH arrhythmia database of Physionet and contaminated signals with motion artifacts at varying signal-to-noise ratios (SNR). The results demonstrate that the algorithm can recognize clean from contaminated signals with an accuracy of 99.5% for signals with an SNR of -10 dB. Once low- and high-quality signals are separated, low-quality signals can undergo additional pre-processing to mitigate the contaminants, or they can simply be discarded. This approach is applied to reduce the false alarms caused by poor-quality ECG signals in atrial fibrillation (AFib) detection algorithms. We propose a signal quality gating system based on DBN and validate it with AFib signals taken from the MIT-BIH Atrial Fibrillation database of Physionet. Without gating, the AFib detection accuracy was 87% for clean ECGs, but it markedly decreased as the SNR decreased, with an accuracy of 58.7% at an SNR of -20 dB. With signal quality gating, the accuracy remained high for clean ECGs (87%) and increased for low SNR signals (81% for an SNR of -20 dB). Furthermore, since the desired level of quality is application dependent, we design a DBN-based algorithm to quantify the quality of ECG signals. Real ECG signals with various types of arrhythmias, contaminated with motion artifacts at several SNR levels, are thereby classified based on their SNRs. The results show that our algorithm can perform a multi-class classification with an accuracy of 99.4% for signals with an SNR of -20 dB and an accuracy of 91.2% for signals with an SNR of 10 dB.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed Dec. 5, 2007). PDF text: XI, 201 p. : ill. ; 7 Mb. UMI publication number: AAT 3271928. Includes bibliographical references. Also available in microfilm and microfiche formats.

Includes bibliographical references (p. 115-120).

Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 02/25/2010). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Gamani Karunasiri, James Luscombe. Includes bibliographical references (p. 59-61). Also available online.

Switchable polar properties of ferroelectric and multiferroic nanostructures are ideal to further diversify applications of mainstream semiconductors. Recent breakthroughs in Scanning Probe Microscopy (SPM) have enabled tailoring of polar domain structures at the nanoscale, which is critical to fabricate polarization-based devices. However, highly inhomogeneous electric fields of biased SPM-tips complicate polarization physics in ferroelectrics and multiferroics. Also, typical diffused phase transition in relaxor bulks originates from coupled inhomogeneities of intrinsic polar nanoregions (PNRs). In this thesis, anisotropic and time-dependent mechanisms were developed to study SPM-tip poled polarization switching in ferroelectric and multiferroic thinfilms. Moreover, frequency-related PNR thermodynamics and its effect on electrocaloric effect of locally disordered relaxors were modeled. Firstly, a three dimensional model was established to clarify tip-poling effect on ferroelectric domain nucleation and growth. The concept of “domain shape invariance” was confirmed through constant aspect ratio obtained for conic ferroelectric nucleus. This domain aspect ratio was found to abruptly decrease under the depolarization effect, saturating domain radius. Further increasing tipvoltage could drive longitudinal breakdown of already reverted domains throughout film thickness. Subsequently, tip-activated evolution of domain wall width in ferroelectric and multiferroic thinfilms was studied via extended Kittle’s law, which included anisotropic and dynamic effects arising from tip-fields. Our calculation results showed that wall width in LiNbO3 varied slightly in an initial stage, followed by a drastic change. This wall variation corresponded to three varying regions of coercive field. Besides, we highlighted three polarization switching modes in BaTiO3 - absence, activation and nonactivation mode. Importantly, distinct switching modes, i.e., breakdown mode of 71° domain switching and activation mode of 180°/109° switching, were revealed to fundamentally control filmorientation dependent multipolarization switching sequence in BiFeO3. Thirdly, Pauli’s mater theory was utilized to bridge microscopic evolution of PNRs and characteristic properties of Pb(Mg1/3Nb2/3)O3 (PMN) relaxors. Temperature dispersion and frequency dependence of PMN dielectric susceptibility were related to nonlinear PNR dynamics over a broad temperature interval. We could not validate PNR-volume predictions of percolation theory above the freezing temperature, but suggest a gradual saturation of PNR volume at lower temperatures. Besides, observed deviations of relaxor permittivity from the Curie-Weiss law were attributed to thermal effects on PNR dynamics and resultant polarization rotations. Furthermore, time-dependent PNR dynamics was proposed to study strong frequency dependence of typical relaxor behaviors. It was implied that frequency effect on PNR coercive field was governed by classic Merz’s-switching, leading to suitability of Vogel-Fulcher law for relaxors bulks. Last but not least, above-mentioned framework for PMN relaxors was incorporated with Landau-Ginzburg-Devonshire thermodynamics and Maxwell relation to better understand recently observed giant electrocaloric (EC) effect of relaxor thinfilms, which is promising for solid-state refrigeration. Three contributions were found to dominate relaxor EC response: temperature-dependent dielectric dispersion, inverse pyroelectric effect and thermally enhanced dielectric stiffness. We emphasized that the EC material with larger dielectric stiffness and smaller correlation length could extend its enormous EC response above Curie temperature. Finally, potential approaches, e.g., by manipulating shape, volume and density of PNRs, were suggested to engineer the EC enhancement in relaxor nanostructures. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy