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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Development of a computational method for inverting dynamic moduli of multilayer systems with applications to flexible pavements

Xu, Qinwu 17 September 2014 (has links)
Most existing computational methods for inverting material properties of multilayer systems have focused primarily on elastic properties of materials or a static approach. Typically, they are based on a two-stage approach: (I) modeling structural responses with a computer program, and (II) estimating layer properties mathematically using the response outputs determined in stage I without interactions with the governing state partial-differential-equation (PDE) of stage I. This two-stage approach may not be accurate and efficient enough for inverting larger scale model parameters. The objective of this research was to develop a computational method to invert dynamic moduli of multilayer systems with applications to flexible pavements under falling weight deflectometer (FWD) tests, thereby advancing existing methods and fostering understanding of material behaviors. This research first developed a finite-element and Newton-Raphson method to invert layer elastic moduli using FWD data. The model improved the moduli seeds estimation and achieved a satisfactory accuracy based on Monte Carlo simulations, addressing the common back-calculation issue of no unique solutions. Consequently, a time-domain finite-element method was developed to simulate dynamic-viscoelastic responses of the multilayer systems under loading pulses. Simulation results demonstrated that the dynamic-viscoelastic-damping-coupled model could emulate structural responses more accurately, thereby advancing existing simulation approaches. By using the dynamic-viscoelastic-response model as one computation module, this research led to the development of a PDE-constrained Lagrangian optimization method to invert dynamic moduli and viscoelastic properties of multilayer systems. The Lagrangian function was used as an objective function, with a regularization term and governing-state PDE constraint. Both the first-order (gradient) and second-order variation (Hessian matrix) of the Lagrangian were computed to satisfy necessary and sufficient optimality conditions, and Armijo rule was modified to determine a stable step length. The developed method improved computation speed significantly, and it is superior for large-scale inverse problems. The model was implemented for evaluating flexible pavements under FWD tests and for inverting the master curve of dynamic moduli of the asphalt layer. Independent computer coding was developed for all numerical methods. The computational methods developed may also be applied to other multilayer systems, such as tissues and sandwich structures at different time and length scales. / text

Deformation Mechanism and Shear Banding Behavior in Amorphous/Nanocrystalline Multilayer System

Lin, I-Chin 26 July 2010 (has links)
Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests because of their unique physical and chemical properties such as good corrosion resistance, larger elastic elongation limit and high strength and hardness. They are also seen as the potential material for micro-electro-mechanical systems (MEMS). However, despite many extraordinary properties in BMGs, BMGs might be difficult to be made into MEMS, different from thin film metallic glasses (TFMGs). Compared with BMGs, few studies have been carried out on TFMGs and their application for MEMS. In this study, efforts have been made to study the properties of multilayered TFMGs. The multilayer thin film selected in this thesis is amorphous/nanocrystalline nanolaminate systems. The micro-pillars of multilayered TFMGs with diameter of 1 £gm are fabricated by using focus ion beam (FIB) and tested in microcompression at room temperature. On nano-indentation test, the phenomenon of strain burst decreases by way of multilayer system. It means that the multilayer system can retard the shear band propagation initiated from the amorphous layers. Under the microcompression test, the deformation of both ZrCu (100 nm)/Cu (50 nm) and ZrCu (100 nm)/Cu (10 nm) multilayer micro-pillars are still dominated by the emission of shear bands in a manner of strain burst to release the energy, but the ZrCu (100 nm)/Cu (100 nm) multilayer thin films reveal continuous deformation and smooth stress-strain curve with no strain burst. First, the sufficient thick of copper layer can absorb more energy from shear deformation of amorphous layer. Second, the copper layer exhibits plastic flow along the transverse direction under the iso-stress deformation. The transverse plastic flow acts as a shear force at interface causing non-stress concentration at amorphous layer. It means that the amorphous layer can be deformed to large plastic strain without stress concentration, causing a homogeneous deformation. According to these two deformation mechanisms, it is possible that the ZrCu (100 nm)/Cu (100 nm) multilayer thin film is better system for improving the ductility of amorphous alloy with a good strength.

Design and characterization of GaAs multilayer CPW components and circuits for advanced MMICs

Lu, Jiaping January 2011 (has links)
With the demand of modern wireless communications, monolithic microwave integrated circuit (MMIC) has become a very promising technique as it is mass-productive, low loss and highly integrated. Microstrip and Coplanar Waveguide (CPW) are both widely used in MMIC. Particularly, CPW has seen a rapid increase on research works recent years due to its unique capability including having less parasitic contribution to the circuit. In this thesis, a novel 3-D multilayer CPW technique is presented. Semi-insulating (S.I.) GaAs substrate, polyimide dielectric layers and Titanium/Gold metal layers are employed in this five-layer structure. The active devices are based on GaAs pHEMTs technology provided by Filtronic Compound Semiconductor Ltd. The fabricated components are simulated and characterized by Agilent Advanced Design System (ADS) and Momentum E.M simulator. A novel Open-short-through de-embedding technique is developed and applied to the passive circuits in order to reduce the impact of pads on probing. A new library of components and circuits are built in this work. Various structures of 3-D CPW transmission lines are designed and characterized to demonstrate the low-loss and highly compact characters. Meanwhile, the influence of various combinations of metal and dielectric layers is studied in order to provide designers with great flexibility for the realization of novel compact transmission lines for 3D MMICs. The effect of temperature on the performance of the transmission lines has also been investigated. Moreover, a set of compact capacitors are designed and proven to have high capacitance density with low parasitics. Finally, based on the extraction of pHEMT parameters from circuit characterization and analysis program (IC-CAP), RF switch and active filter MMICs have been designed and simulated to provide references for further development of 3-D multilayer CPW circuits.

Fabrication and characterisation of 3D multilayer circuits for compact mmic applications

Kyabaggu, Peter Kalemeera Balwayo January 2015 (has links)
The expansion of the market for wireless communications and sensors has led to the recent increase in demand for highly integrated MMICs for millimetre-wave wireless applications. These applications require MMICs that offer low cost, high integration, high functionality and high performance as well as simpler, more rapid development. An effective way of meeting these requirements and realising highly integrated MMICs is by employing multilayer three-dimensional (3-D) MMIC technology. The research work described in this thesis presents the modelling and characterisation of newly developed passive components such as coplanar waveguides (CPWs), thin-film microstrips (TFMSs) and transition transmission line structures using 3-D multilayer technology. These structures have been developed with low losses in mind, along with variable characteristic impedances and miniaturised size. With the knowledge obtained from the design and optimisation of CPW and TFMS transmission lines, new and improved compact CPW-to-TFMS transitions have been successfully achieved. Accurate electromagnetic modelling was carried out using the 2.5-dimensional ADS Momentum simulator. Newly improved fabrication techniques were employed to produce reported compact microwave components and circuits, in order to lower cost and simplify the process. Compact MMIC components were fabricated using a seven-layer fabrication procedure on semi-insulating GaAs substrate where pseudomorphic high electron mobility transistors (pHEMTs) pre-fabricated by the manufacturer. High frequency on-wafer RF measurements were carried out using Agilent 8510 series vector network analysers (VNAs). In-depth analysis and comparisons between the simulated and measured results are provided. Analysis of active MMIC components was achieved by developing small-signal equivalent circuits of the GaAs pHEMTs, and knowledge extracted from this analysis was employed in the development of large signal models of the pHEMT devices. Furthermore, the design and characterisation of a few MMIC circuits, such as limiters and amplifiers, demonstrates the integration of multilayer CPW passive components with prefabricated pHEMTs. These components are compatible with RF systems-on-chip sub-systems providing low cost, low loss performance with their ease of fabrication.

Template-assisted multilayer electrodeposition: An approach to top-down designable, surface/volumetric hierarchical nanostructures

Kim, Min Soo 27 May 2016 (has links)
Driven by the emerging interest in the design and realization of structures with co-existing micro- and nanoscale features, various nanofabrication approaches are being developed. We show that the selective, conformal growth of a multilayer structure is a promising route for the controlled realization of various structures with size-hierarchy, including both surface (i.e., the structures of which functionalities are characterized by the interaction between their surface, and external systems, such as self-cleaning, superhydrophic substrates with dual-scale topography), and volumetric (i.e. composite materials of which functionalities rely on the intrinsic properties of nanostructures distributed throughout their volume, such as giantmagnetoresistance sensors) structures. This is realized based on a sequential multilayer electrodeposition guided by an insulating substrate with predesigned topography, referred to as template-assisted multilayer electrodeposition process. Various multiscale, multidimensional surface and volumetric hierarchical structures are demonstrated of which size scale of the nanostructures are defined by the individual layer deposition parameters, while their position and overall geometry are defined by that of the template. These structures include (1) large area (> 1 cm^2), planar, or non-planar surfaces comprised of anisotropic, nanoscale surface relief structures of wide-ranging size scale (10 nm-1 micron); and (2) thick (10-100 micron), volumetric composite material in which individual metallic layers of micron, or submicron scale thicknesses are electrically insulated from the adjacent layers by interlamination insulating layers of similar thicknesses. The utility of the fabricated structures is evaluated in a few potential application domains, i.e., nanolithography, self-cleaning, and high frequency magnetic devices.

Multilayer scalable coupler with high directivity

Basta, Nina Popovic 21 September 2015 (has links)
This thesis addresses the design, analysis, and experimental validation of a high-directivity and high coupling microwave directional coupler. The motivating application is in broadband signal routing between cores of multi-core processors, where the delay of simple wire interconnects introduces unacceptable latency. The performance goals include scalability with frequency, a coupling coefficient of 3 dB, directivity larger than 40 dB, high return loss, low insertion loss below 3 dB at the center frequency, and small footprint. The approach to this problem taken in the thesis is a combination of edge and broad-side coupling in a multi-layer, multi-conductor microstrip coupled-line system. The two coupling mechanisms between neighboring pairs of coupled lines, along with appropriate end interconnections, allow for reduced size and design that achieves equal propagation velocities for the different modes supported by the five-conductor guiding structure that contribute to coupling. To validate the approach, a coupler designed for operation at 1 GHz is demonstrated to have a isolation of -22 dB with a coupling coefficient of 3\,dB and a return loss of -20 dB. The coupler is implemented on a FR-408 substrate with a permittivity of 3.66 and 1.17mm and 0.17mm thicknesses, and a total area of 12.65 cm^2. Three metalization layers are used in the design, with edge and broad-side coupled pairs of lines on the top two layers and diagonal end interconnects between the top and bottom lines. The coupler design is then scaled to 3 GHz by shortening the coupled-line length, and established -24 dB isolation, coupling of 3 dB, return loss of -20 dB, and has a total area of 6.9 cm^2. The analysis of the coupler shows that full-wave electromagnetic modeling agrees well with measurements and is necessary during the design process, while circuit analysis with built-in coupled-line models shows poorer agreement with experimental data. A tolerance analysis shows that the coupler performance is most sensitive to milling precision and separation between coupled-lines. Based on the measured and simulated results, it is shown that this type of coupler can be further scaled to higher frequencies and on-chip implementations for signal distribution in multi-core processors, or any other application where a number of components need to be interconnected with low latency and no reflection.

Effect of MgO doping on the microstructure development of BaTiO3

Lee, Hwan-Wen 06 August 2008 (has links)
Commericially available BaTiO3 powder was die-pressed to discs, and sintered by a two-stage firing consisting of reducing in low oxygen partial pressures (pO2) and re-oxidizing in a higher pO2 to simulate the industrial process of manufacturing the multi-layer ceramic capacitors(MLCC). Both undoped and MgO-doped discs as well as commercial MLCC chips, provided by Ferro Electronic Material Systems, have been investigated for sintered microstructures using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), crystalline phases using the X-ray diffractometry (XRD), and dielectric properties using the frequency response analysis. A comparison between the microstructures is made in order to look for the microstructure origin of the macroscopic behaviour, e.g. dielectric properties.It is found that the crystalline phases have changed frompredominantly tetragonal to pseudo-cubic with MgO > 0.5 mol.%. Apart from grain growth being effectively suppressed in MgO-doped compositions, grains containing the characteristic ferroelectric domains in undoped samples have decreased significantly in number. The indication is that Mg2+ dissolving into the BaTiO3 lattice, substituting for the Ti4+ site reduces the c/a ratio. However, unlike what was reported before, no direct experimental evidence is found to support that grain growth inhibition is effected by Mg2+ segregation to grain boundaries.Dislocation loops are observed ubiquitously in all samples, although bothMgO doping and low pO2 have decisive effect on their density in sintered grains. In MLCC chips, the microstructure is characterised by core-shell grains representing the dissolution of solutes, and modulated grains representing the ordering of chemical defects, e.g. substitutional defects and oxygen vacancies forming defect clusters.Residual pores located intragranularly in the MLCC chips are also observed, and its origin discussed. The formation of such pores is attributed to vacancy condensation which is enhanced by the increased oxygen vacancies due to MgO doping, as an acceptor, and by low pO2 firing.

The Growth of the Magnetic Multilayer and Relative Properties

Ho, Yen-Hsun 22 August 2008 (has links)
From the discovery of GMR effect since 1988,spintronic has been extensively developed. Research and application of relative GMR, CMR and TMR topics have progressed rapidly. In the year of 2007, the Nobel prize of physics was awarded to Albert Fert and Peter Grünberg for the great achievement on the research of GMR. The application of development on MRAM is a very hot subject recently and the main operating constructions of MRAM are MTJ. In this thesis, La0.67Ca0.33MnO3¡BLa0.67Sr1.33MnO4 and La0.8Ba0.2MnO3 of CMR materials were growth to multilayer to investigate the properties and characters of the films, in order to built up the MRAM based on CMR MTJ¡¦s.

Preparation of LB films of alkyl-amine complexes and their optical ellipsometric and X-ray mirror properties

Hariyadi January 1999 (has links)
No description available.

High power rotary microgenerator with multipole and multilayer planar microcoil

Wu, Tsung-Tien 01 July 2005 (has links)
MEMS process offers many advantages that the microsystem can be downscaled and can be combined with integrated circuit (IC). This technique has been successfully applied to micromotor, micropump, and microelectric apparatus but there has been existing problems of independent and compact power supply system. Hence this study presents an electromagnetic rotary microgenerator, mainly consisting of multilayer planar Cu microcoil and multipolar hard magnet of Nd/Fe/B by sintering. The layout of the microgenerator is 9 9 1 mm3 in volume. The paper also presents design and analysis of a multipolar rotary electromagnetic microgenerator. Theoretical mathematic model is derived to predict the power generation. Experimental results are compared with simulations. The experimental result shows good agreement with simulations. The preliminary experimental result reveals that this microgenerator with eight magnet poles and four-layer Cu planar microcoil generates an output voltage of 569 mV at 213.7 Hz frequency.

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