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Dissertations / Theses on the topic 'Multi-layered structures'
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Ortigoza-Guerrero, Lauro. "Resource allocation strategies for multi-layered cellular structures." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324885.
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Yildirim, Egemen. "Development Of Multi-layered Circuit Analog Radar Absorbing Structures." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614314/index.pdf.
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A fast and efficient method for the design of multi-layered circuit analog absorbing structures is developed. The method is based on optimization of specular reflection coefficient of a multi-layered absorbing structure comprising of lossy FSS layers by using Genetic Algorithm and circuit equivalent models of FSS layers. With the introduced method, two illustrative absorbing structures are designed with -15 dB reflectivity for normal incidence case in the frequency bands of 10-31 GHz and 5-46 GHz, respectively. To the author&rsquos knowledge, designed absorbers are superior in terms of frequency bandwidth to similar studies conducted so far in the literature. For broadband scattering characterization of periodic structures, numerical codes are developed. The introduced method is improved with the employment of developed FDTD codes to the proposed method. By taking the limitations regarding production facilities into consideration, a five-layered circuit analog absorber is designed and manufactured. It is shown that the manufactured structure is capable of 15 dB reflectivity minimization in a frequency band of 3.2-12 GHz for normal incidence case with an overall thickness of 14.2 mm.
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LI, GUOHONG. "Variable Kinematic Finite Element Formulations Applied to Multi-layered Structures and Multi-field Problems." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729361.
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Schneider, Tyler. "MULTI-LAYERED TUBING AND PIPING: TECHNOLOGY DEVELOPMENT AND TRANSFER LEADING TO NEW DIMENSIONS IN ANNULAR LAYERED STRUCTURES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1567782483369336.
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Koston, E. "Fatigue crack monitoring in multi-layered aircraft structures using guided ultrasonic waves." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/516138/.
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The detection of fatigue cracks at fasteners in the sub layers of multi-layered aircraft structures can be problematic using conventional nondestructive testing methods. In this thesis the sensitivity of low frequency guided ultrasonic waves to detect these defects is studied. Guided ultrasonic waves typically have energy distributed through the thickness of such structures and allow for defect detection in all sub-layers, but have wavelengths larger than commonly used in bulk wave ultrasonic testing. The model aerospace multi-layered structure investigated consists of two aluminium plate strips adhesively bonded using a paste adhesive with a fastener hole. Guided waves were excited by placing piezoelectric (PZT) transducers on the surface of the structure. Experimentally the wave propagation and scattering was measured using a laser interferometer. The wave propagation was studied numerically using Semi-Analytical Finite-Element (SAFE) calculations and 3D Finite Element (FE) simulations. Thickness and width mode shapes of the guided waves were identified from the SAFE simulations. By placing PZT discs across the width of the structure the excited exural wave modes could be controlled to an extent. The thickness mode shapes of these waves are similar to those in a large multi-layered plate structure. 3D FE simulations predict a similar amplitude change due to a defect in these structures. Fatigue crack growth monitoring on tensile specimens was realized, measuring the amplitude at a single point. The measured changes in the amplitude of the ultrasonic signal due to a defect agree well with 3D FE simulations. These investigations found that using low frequency guided ultrasonic waves defects through the thickness of a hidden sub layer can be detected from measurements on the undamaged, accessible layer.
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Ahmad, Muhammad Saeed. "Study of dynamic behaviour of multi-layered structures subjected to blast loading." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/10005.
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The objective of this research work is to assess the response of multi-layered plates in comparison to single plates to gain physical understanding of different phenomena taking place at micro level during localized blast loading. Since layered plates have been shown to give improved ballistic performance under certain circumstances, it is useful to ascertain and understand the influence of layering on blast performance. This investigation is carried out both experimentally and numerically. A finite element model was developed to design the blast experiments for two different steels of various thicknesses.
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Oun, Hatem Ahmed. "Pressure-drop studies in porous multi-layered inconel structures : potential for aero-engine sealing application." Thesis, University of Nottingham, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.716833.
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Open-cell porous metals and alloys, based on polymer foam replication techniques, have been performing significantly well and, in many cases, replacing traditional porous metals, including metal foams, in various applications because of their unique properties and structural features including high porosity, semi-uniform structure, light weight and high surface to volume ratio. In applications requiring flow of fluids (gas, liquid or both) through open-cell porous structures, for instance in multi-stage filters, heat exchangers, water purification and the storage and transfer of liquid, pressure-drop and flow characteristics of the fluid are essential parameters in application design and performance. Despite the fact that pressure-drop is often sought to be minimised, high pressure-drop is sometimes required such as when used as abradable seals in jet engines. In this work, the structure of Inconel 625, open-cell porous metals (with nominal cell sizes 450, 580, 800 and 1200 pm) were studied in detail using a series of imaging and morphological techniques. The effect of airflow velocity, in the range of 0-70 m s'1, on the pressure-drop characteristics for bulk and structurally tailored, diffusion bonded, multilayered, open-cell porous structures, as a function of thickness (affected by sectioning), density (affected by compression) and structural alterations (affected by multi-pore sized insets, porous metal stacking and air gaps), were thoroughly investigated. As the air flow velocity increases, fluid properties tend to change and drag force increases in comparison with the viscous effect causing the pressure drop data to deviate from the nonlinear, quadratic Forchheimer model into a cubic equation at a velocity value higher than 20 m s'1. The need for accurate pinpointing of the different regimes (Darcy, Forchheimer and Turbulent), which enables precise determination of the permeability (K) and form drag coefficient (C), was highlighted. Understanding the pressure-drop behaviour for multilayered, open cell porous structures will offer the possibility for combining layers with different porosities and pore sizes giving the ability to tailor the structure to achieve bespoke flow conditions for demanding applications. For example, the use of a 9 mm thick porous structure in three different configurations (bulk, stacked and gapped) causes the pressure-drop to change drastically, while having the same weight (3.38g), thus, the potential for mass-efficient porous structures is readily achievable.
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Köberle, Patrick [Verfasser]. "Ground-state structures and dynamics of dipolar Bose-Einstein condensates in single and multi-layered traps / Patrick Köberle." München : Verlag Dr. Hut, 2011. http://d-nb.info/1016531664/34.
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Li, Tianyu. "On the Formulation of a Hybrid Discontinuous Galerkin Finite Element Method (DG-FEM) for Multi-layered Shell Structures." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/82962.
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A high-order hybrid discontinuous Galerkin finite element method (DG-FEM) is developed for multi-layered curved panels having large deformation and finite strain. The kinematics of the multi-layered shells is presented at first. The Jacobian matrix and its determinant are also calculated. The weak form of the DG-FEM is next presented. In this case, the discontinuous basis functions can be employed for the displacement basis functions. The implementation details of the nonlinear FEM are next presented. Then, the Consistent Orthogonal Basis Function Space is developed. Given the boundary conditions and structure configurations, there will be a unique basis function space, such that the mass matrix is an accurate diagonal matrix. Moreover, the Consistent Orthogonal Basis Functions are very similar to mode shape functions. Based on the DG-FEM, three dedicated finite elements are developed for the multi-layered pipes, curved stiffeners and multi-layered stiffened hydrofoils. The kinematics of these three structures are presented. The smooth configuration is also obtained, which is very important for the buckling analysis with large deformation and finite strain. Finally, five problems are solved, including sandwich plates, 2-D multi-layered pipes, 3-D multi-layered pipes, stiffened plates and stiffened multi-layered hydrofoils. Material and geometric nonlinearities are both considered. The results are verified by other papers' results or ANSYS.Master of Science
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Su, Rong. "Improved inspection and micrometrology of embedded structures in multi-layered ceramics : Development of optical coherence tomographic methods and tools." Doctoral thesis, KTH, Mätteknik och optik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-144595.
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Roll-to-roll manufacturing of micro components based on advanced printing, structuring and lamination of ceramic tapes is rapidly progressing. This large-scale and cost-effective manufacturing process of ceramic micro devices is however prone to hide defects within the visually opaque tape stacks. To achieve a sustainable manufacturing with zero defects in the future, there is an urgent need for reliable inspection systems. The systems to be developed have to perform high-resolution in-process quality control at high speed. Optical coherence tomography (OCT) is a promising technology for detailed in-depth inspection and metrology. Combined with infrared screening of larger areas it can solve the inspection demands in the roll-to-roll ceramic tape processes. In this thesis state-of-art commercial and laboratory OCT systems, operating at the central wavelength of 1.3 µm and 1.7 µm respectively, are evaluated for detecting microchannels, metal prints, defects and delaminations embedded in alumina and zirconia ceramic layers at hundreds of micrometers beneath surfaces. The effect of surface roughness induced scattering and scattering by pores on the probing radiation, is analyzed by experimentally captured and theoretically simulated OCT images of the ceramic samples, while varying surface roughnesses and operating wavelengths. By extending the Monte Carlo simulations of the OCT response to the mid-infrared the optimal operating wavelength is found to be 4 µm for alumina and 2 µm for zirconia. At these wavelengths we predict a sufficient probing depth of about 1 mm and we demonstrate and discuss the effect of rough surfaces on the detectability of embedded boundaries. For high-precision measurement a new and automated 3D image processing algorithm for analysis of volumetric OCT data is developed. We show its capability by measuring the geometric dimensions of embedded structures in ceramic layers, extracting features with irregular shapes and detecting geometric deformations. The method demonstrates its suitability for industrial applications by rapid inspection of manufactured samples with high accuracy and robustness. The new inspection methods we demonstrate are finally analyzed in the context of measurement uncertainty, both in the axial and lateral cases, and reveal that scattering in the sample indeed affects the lateral measurement uncertainty. Two types of image artefacts are found to be present in OCT images due to multiple reflections between neighboring boundaries and inhomogeneity of refractive index. A wavefront aberration is found in the OCT system with a scanning scheme of two galvo mirrors, and it can be corrected using our image processing algorithm.QC 20140428
Multilayer (FP7-NMP4-2007-214122)
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Krimi, Soufiene [Verfasser]. "Non-Destructive Terahertz Sensor for In-line Contactless Thickness Measurement and Quality Control of Multi-Layered Structures / Soufiene Krimi." München : Verlag Dr. Hut, 2016. http://d-nb.info/1103872869/34.
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Grédé, Audrey. "Modélisation des chocs d’origine pyrotechnique dans les structures d’Ariane5 : développement de modèles de propagation et d'outils de modélisation." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2009. http://www.theses.fr/2009ECAP0006/document.
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La compréhension et l’amélioration de l’environnement vibratoire des charges utiles demande la mise au point de démarches prédictives maîtrisées qui permettent de comprendre les phénomènes de transmission des ondes de chocs d’origine pyrotechnique dans le lanceur Ariane5. Plus particulièrement, la maîtrise du comportement transitoire des coques sandwichs en nid d’abeilles, principaux constituants de l’Adaptateur de Charges Utiles – structure porteuse des satellites, est nécessaire pour prédire les vibrations au pied des équipements électroniques des satellites et des lanceurs. Cette problématique présente un caractère multi-échelle tant d’un point de vue temporel (charge mobile supersonique, temps d’analyse) que spatial (dimensions des structures du lanceur, taille des cellules en nid d’abeilles, longueurs d’ondes liées aux hautes fréquences). Celui-ci a été traité dans cette thèse en s’appuyant d’une part, sur une qualification à la fois analytique et numérique des modèles classiques homogénéisés des plaques sandwichs en nid d’abeilles pour la gamme de fréquence mise en jeu et d’autre part, sur une application des stratégies de remaillage adaptatif pour la propagation des ondes développées dans le cadre de la méthode de Galerkin espace-temps discontinue en temps. Deux catégories de modèles de plaques épaisses ont été ainsi construites dans le but d’enrichir la cinématique classique de plaques épaisses de Mindlin-Reissner qui s’est avérée être insuffisante pour correctement représenter le comportement dynamique hors-plan des plaques sandwich en nid d’abeilles. Ainsi ont été analysés les modèles dits monocouches basés sur un enrichissement de la cinématique par ajout de degrés de liberté dans l’épaisseur, et les modèles multicouches composés d’une superposition de trois plaques avec une homogénéisation séparée des matériaux. Il a été montré que ces deux sortes de modèles améliorent la description des phénomènes de hautes fréquences, notamment ceux de flexion et de cisaillement transverse qui sont plus délicats à retranscrire. Toutes les études numériques ont été effectuées avec un code éléments finis qui emploie des solveurs adaptatifs dynamiques basés sur la méthode de Galerkin espace-temps discontinue en temps. Cette méthode d’intégration en temps introduit un amortissement numérique dépendant du pas de temps et qui peut interférer avec un amortissement physique susceptible d’être introduit dans un modèle numérique et conduire au final à un amortissement total différent de celui qui est attendu. Cette interaction a été analysée et mise en évidence dans ce travail à travers l’introduction de l’amortissement de Rayleigh dans les modèles de propagation de chocs. Les outils et les modèles de propagation ainsi développés ont été validés sur plusieurs structures académiques et industrielles. Des comparaisons avec des données expérimentales sur des structures industrielles de grande taille, plus particulièrement sur un Adaptateur de Charges Utiles d’Ariane5, sont effectuées et soulignent la cohérence de notre approche ainsi que la fiabilité et l’efficacité des modèles de propagation proposésReliable and efficient numerical models for the pyrotechnic shock wave propagation in structures of the Ariane5 launcher are necessary for a good understanding and a predictive analysis of the payload vibration environment. More precisely, the correct modeling of the dynamic behaviour of the honeycomb sandwich shells, the main material composing the payload adaptor, is essential to control the vibration environment of the payload and the embarked electronic equipments and so to prevent them from damages caused by the shock wave propagation. The topic is obviously a multi-scale problem from both temporal and spatial points of view : short time intervals imposed by supersonic moving loads vs. large total time interval that the slowest waves need to travel throughout the adaptor ; very short wavelengths of high frequency waves, and very small size of the honeycomb cells vs. large structure dimensions. To take into account all involved space-time scales in a reliable and efficient way, the herein study is based both on the analytical and numerical qualification of the classical homogenized models of honeycomb sandwich shells for the frequency range introduced by the pyrotechnic shock wave, and on a dynamic solver based on the well-known space-time discontinuous Galerkin method, allowing the use of adaptive remeshes for the wave propagation. The classical Mindlin-Reissner’s kinematics of thick plates being inefficient to correctly represent the dynamic out-of-plane behaviour of the honeycomb sandwich plates, two kinds of its enrichment are considered : One-layered models based on an enrichment of the kinematics by adding degrees of freedom in the thickness, and multi-layered models composed of a superposition of three plates with separated material homogenisations. It has been shown theoretically and numerically that, both types of enrichment allow more precise descriptions of flexure and transverse shear modes in the high frequency range. However, the multi-layered models give much more promising results, as the important role played by the honeycomb core for the transverse shear behaviour of the whole sandwich is not “smeared” in a one-layered homogenized model. All the numerical studies were conducted with a finite element code which uses a dynamic solverbased on the time discontinuous space-time Galerkin method. The built-in numerical damping of this solver can interfere with a physical damping potentially introduced by the numerical model and results in a global damping totally unexpected. This interaction has been analysed and underlined in this work thanks to the introduction of the Rayleigh damping in the shock wave propagation models. Theoretical and numerical tools and propagating models thus developed have been validated on several academic and industrial structures. Comparison with experimental data on large size industrial structures, especially a real size payload adaptor, is performed and emphasizes the coherence of our approach and the reliability and the efficiency of the proposed propagating models
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Loader, Charlotte Bree. "Structural properties of multi-layered materials." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342222.
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Wu, G. P. "Structural performance of multi-layered laminated glass plates." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636698.
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The work presented in this thesis focus on analysing the structural performance of multi-layered laminated glass places subjected to uniform pressure loading. Numerical simulations using ANSYS finite element software has been performed to analyse the behaviour of laminated glass plates. Theoretical laminated glass beam models that represent the interaction of forces between PVB interlayer and glass have been presented. Based on the formulation of theoretical models, a new modelling technique using shell and link elements has been proposed. The behaviour of glass plate is captured by the shell element and the shearing behaviour of PVB interlayer is simulated by a structure constructed of link elements. The shearing behaviour of PVB interlayer can be modelled as linear, if the shear strain does not reach the non-linear limit. The modelling technique has been applied to model experimental results provided by the Public Services Agency and close agreement of results have been obtained. Parametric studies have been carried out on laminated glass models and discussions have been made. Using two non-dimensional parameters, design equations for 3-ply, 5-ply and 7-ply laminated glass plates have been proposed. For the case of 3-ply laminated glass plates, it is discovered that the design equations with 40MPa and 45MPa design stresses predicted close agreement to experimental results. For the case of 5-ply and 7-ply laminated glass plates. 28MPa and 33MPa design stresses predicted close agreement to experimental results. For samples with standard interlayer thickness, same plate dimensions and glass thickness, laminated glass plates can be stronger than monolithic glass plates. Additionally in most cases, the load bearing capacity of laminated glass plates with more layers is higher or comparable to laminated glass plates with fewer layers. This is caused by the redistribution of bending and membrane stresses due to early or late development of membrane effect.
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Silva, Renato Marques Correa da. "On the structural mechanics of multi-layered subsea pipelines." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299721.
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Yuan, Huali. "Modeling VOCs Emissions from Multi-layered Structural Insulated Panels(SIPs)." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28823.
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Indoor air quality is recognized as one of the most important environmental concerns, since people spend almost 90% of their lifetime indoors. Indoor sources of volatile organic compounds (VOCs) are a determinant of air quality in houses. Many materials used to construct and finish the interiors of new houses emit VOCs. These emissions are a probable cause of acute health effects and discomfort among occupants. Ventilation is another determinant of indoor air quality in houses, because it serves as the primary mechanism for removal of gaseous contaminants generated indoors. Thus, higher contaminant concentrations are expected at lower ventilation rates given constant emission rates. The trend in new construction is to make house envelopes tighter for higher energy efficiency. The use of Structural Insulated Panels (SIPs) in new construction and major renovation to create very tight building envelopes is one popular approach to realizing this goal. The basic SIPs configuration uses oriented strand board (OSB) and polystyrene foam (PSF) in a multi-layered sandwich-like structure. Specific benefits of SIPs include lower energy consumption, stronger more durable structures and better resource efficiency. These advantages make panelized systems very attractive from both environmental impact and energy use perspectives. However, there is a potential for houses constructed with SIPs to have degraded air quality relative to conventionally constructed houses that utilize fewer engineered wood products. OSB emits pentanal and hexanal, two odorous aldehydes. These contaminants originate in the wood drying process through the breakdown of wood tissue and are, thus, inherent to most engineered wood products. The PSF in SIPs is a major source of styrene. The large surface area of installed SIPs systems (typically the entire exterior shell), combined with the resulting decrease in ventilation rate due to very low infiltration, exacerbates the indoor air problem. Thus, the potential release of volatile contaminants must be taken into careful consideration when designing homes constructed with SIPs. The ability to predict and ultimately minimize the negative impact of panel systems on indoor concentrations of contaminants of concern would be extremely useful for advancing housing technologies. No prior investigations of VOC emissions from SIPs have been reported in the literature.
Two main methods are used to characterize emissions from building materials: chamber studies and mathematical modeling. While chamber studies are costly and time-consuming, mathematical modeling is becoming an economical and effective alternative. Physically-based models are especially useful because they provide insight into the governing mechanisms and the factors that control the emissions process. Although emissions from building materials have traditionally been empirically characterized in chambers, we have recently validated a mechanistic model that predicts VOC emissions from vinyl flooring. The approach involved independently measuring C0 (the initial material-phase concentration), D (the material-phase diffusion coefficient), K (the material/air partition coefficient) and then predicting the emission rate a priori using a fundamental mass-transfer model We now wish to generalize this approach and use it to predict emissions from multi-layered SIPs. To begin with, we will apply a single-layer model to predict emissions from each of the two SIP components: OSB and PSF. Once this has been accomplished, it should be possible to develop a multi-layer model to predict emissions from the composite SIPs.
Our first research objective was to characterize transport of volatile organic compounds (VOCs) in polystyrene foam (PSF), a diffusion-controlled building material. The sorption/desorption behavior of the polystyrene foam was investigated using a single-component system. A microbalance was used to measure the sorption/desorption kinetics and to obtain equilibrium relationships. Hexanal and styrene were selected as the target compounds. While styrene transport in PSF can be described by Fickian diffusion with a symmetrical and reversible sorption/desorption process, the hexanal transport process exhibited significant hysteresis, with desorption being much slower than sorption. To address this hysteresis, a porous media diffusion model that assumes local equilibrium governed by a non-linear Freundlich isotherm was developed. The model was found to conform closely to the experimental kinetic data for both sorption and desorption. By incorporating the Freundlich sorption mechanism into the traditional Fickian diffusion model, the hysteresis in the hexanal transport process in PSF was explained.
Contaminant emissions from building materials may tail extensively and require longer times to desorb than absorb. This slow desorption or hysteresis problem has been an obstacle to understanding VOC emissions from building materials. The overall goal of our second research objective was to (i) develop a predictive nonlinear emission model by incorporating a local Freundlich sorption equilibrium to account for the slow desorption; (ii) validate the new nonlinear emission model using independent chamber data; and (iii) compare the new nonlinear emission model with a previously published linear emission model. Styrene in polystyrene foam (PSF) and hexanal in oriented strand board (OSB) were selected as the target compounds and materials, respectively. Sorption/desorption kinetic experimental data show that while styrene sorption/desorption in PSF is symmetrical, hexanal sorption/desorption in OSB is not symmetrical. For hexanal in OSB, slower desorption was observed. Model validation results show that while the simple linear emission model can predict styrene emissions from PSF, it underestimates hexanal emissions from OSB. With the new nonlinear emission model developed in this research, hexanal emission from OSB can be predicted. These results suggest that local sorption equilibrium needs to be considered when predicting the emission rate of polar compounds from building materials.
The final objective was to develop a new multi-layer model for a layered SIP system. Composite layered building materials are widely used in indoor environments due to their environmental and energy advantages. However, the tight structure may result in degraded indoor air quality and the potential release of volatile organic compounds (VOCs) from these layered materials must be considered. A theoretical physically-based diffusion model for predicting VOCs emissions from such multi-layer materials is described in this research. It is assumed that the individual layers are flat homogeneous slabs, that internal mass transfer is governed by diffusion, and that the indoor air is well mixed. For each layer, the material-phase diffusion coefficient (D), the material-phase partition coefficient (K), and the initial material-phase concentration (C0) are the key model parameters. In this model, fugacity is used to numerically solve the model because this eliminates the discontinuities in concentration at the interface between layers. This overcomes an insurmountable obstacle associated with numerically simulating mass transfer in composite layers. The fugacity-based numerical model is checked by comparing predicted concentrations to those obtained with a previously published analytical model for double-layered materials. In addition, transport of hexanal and styrene within, and emissions of hexanal and styrene from, multi-layer Structural Insulated Panels (SIPs) are simulated to demonstrate the usefulness of the model. These preliminary results establish the viability of the fugacity approach. Finally, the multi-layer layer model is used to demonstrate the impact that barrier materials can have. Results show that contaminant gas phase concentration can be reduced greatly with a barrier layer on the surface. This deomonstrates the potential of thin barrier layers to minimize the environmental impact of panelized systems. Future work will focus on a more complete experimental validation of the multi-layer model.Ph. D.
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Dressler, Marc. "Theoretical and experimental modeling of ultrasonic waves in multi-layered media." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/21535.
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Sirikumara, Henaka Rallage Hansika Iroshini. "Engineering structural/electronic properties of layered Selenides : A multi-scale modeling approach." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1840.
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Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.
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Huang, Yu Ping. "Predictions of static and dynamic performance of multi-layered spiral strands under various loading conditions." Thesis, London South Bank University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334631.
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The upper bound to the frictional damping of axially preloaded single layer strands subjected to cyclic bending to a constant radius of curvature has been determined. The theoretical model includes a modified frictional approach which takes no-slip to full-slip friction transition over the individual interwire contact patches into account. Numerical results show that cable damping may be increased by increasing the number of wires and/or increasing the lay angle. Using the orthotropic sheet concept, and employing established results regarding the frictional contact of non-spherical bodies, an analytical model has been proposed for estimating the bending stiffness and hysteresis of axially preloaded multi-layered spiral strands undergoing uniform cyclic bending movements. Also investigated are the bending characteristics of axially preloaded sheathed spiral strands experiencing high external hydrostatic pressures such as those in deep water platfonn applications. Based on a series of theoretical parametric studies on a number of realistic multi-layered sheathed spiral strands, a series of straightforward formulations aimed at practicing engineers were developed. Numerical results are presented for a number of realistic spiral strands with diameters as large as 184 mm, covering the full range of practical wire diameters and lay angles, and experiencing a wide range of mean axial loads and imposed radii of curvature. A theoretical model for determining WIre stresses III helical strands undergoing bending to a constant radius of curvature has also been proposed. The individual wire bending stresses are shown to be composed of two components -i.e. those due to presence of interlayer friction and those due to wires bending about their own neutral axes. The final theoretical results show that the maximum wire axial stress components due to interlayer friction are much greater than the corresponding single wire bending stresses. Based on theoretical studies on bending hysteresis of axially preloaded multi-layered spiral strands and previously reported experimental observations, the structural damping factor in axially pre loaded spiral strands undergoing lateral vibrations under, say, vortex shedding conditions can now be predicted. Closed-form solutions for predicting the extensional-torsional wave speeds and displacements in axially pre loaded spiral strands experiencing specific forms of impact loading at one end with the other end fixed, have been developed. Finally, a theoretical model for estimating the recovery length of a fractured wire in parallel wire strands prestressed by external wrapping or clamping have been developed. In this model, the transition from the full-slip to no-slip interwire friction, as one moves away from the fractured end, is taken fully into account.
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Popli, Nipun. "Multi-layered Energy Conversion and Frequency Control in Complex Electric Power Systems." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/916.
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The main performance objective in an electric power grid entails timely and efficient generation and delivery to the time-varying electricity demand. As the electricity industry is witnessing proliferation of the mainstream renewables, the minute-by-minute variations in wind and solar power generation may result in temporary electricity scarcity that jeopardizes grid stability and quality of service. The evolving electricity markets are aimed at incentivizing the conventional generators to reinforce their operating flexibility. This dissertation concerns the goal of enhancing the dynamic response rates of interconnected controllable resources by means of a multi-layered fuel input control of electrically coupled heterogeneous energy conversion components. Both power engineering and large-scale control contributions are made in support of this enhancement. First, improved fuel input controls are designed to enable flexible physics-based energy conversion dynamics required by the interconnected grid. To efficiently utilize the resources load-following and regulation problems are stated. The efficacy of proposed fuel input control designs in enhancing the dynamic response rates is illustrated on IEEE 14-bus system. Second, the problem is formalized as multi-input multioutput time-varying trajectory tracking based on a decentralized spatiotemporal composite control design. The concepts of vector-Lyapunov function and singular perturbation are invoked to formalize model decompositions, over space and time, respectively. Next, the assumptions for model simplifications are relaxed and the problem of parametric uncertainty is addressed. A minimumcost resilient co-design approach is introduced for storage-sensors-communication channels in a complex electric power grid. The notion of selective strong structural fixed modes is explored as a characterization of feasible decentralized control laws for an arbitrary system realization satisfying a pre-specified structure. Finally, it is proposed that planning of generation portfolio must be driven by the objective of maintaining adequate operating flexibility in the system. The goal is to ensure sufficient ramp capacity to sustain the significant integration of intermittent renewable resources.
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Zafra-Camón, Guillermo. "Calculation of global properties of a multi-layered solid wood structure using Finite Element Analysis." Thesis, Uppsala universitet, Tillämpad mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-298677.
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Finite Element Method (FEM) is a powerful numerical tool which, combined with the fast development of Computer Science in the lastdecades, had made possible to perform mechanical analysis of a widerange of bodies and boundary conditions. However, the complexity of some cases may turn the calculationprocess too slow and sometimes even unaffordable for most computers. This work aims to simplify an intricate system of layers withdifferent geometries and material properties by approximating itthrough a homogeneous material, with unique mechanical parameters.Besides the Finite Element analysis, a theoretical model is created, in order to understand the basis of the problem, and, as a firstapproach, check whether the assumptions made in the FEM model areacceptable or not. This work intends to make a small contribution to the understandingof the mechanical behaviour of the Vasa vessel, which will eventuallylead to the design of a new support structure for the ship. The preservation of the Vasa is a priority for the Swedish Property Board, as it is one of the main monuments of Sweden.
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Wallace, Efoé Rodrigue. "On the rolling contact between multi-layered bodies, application to tire-pavement modelling." Thesis, Lyon, 2022. http://theses.insa-lyon.fr/publication/2022LYSEI014/these.pdf.
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Cette thèse a été consacrée au développement d’un outil numérique de dimensionnement des chaussées. En effet, la récurrence des dégradations observées à la surface des chaussées, pousse la recherche scientifique à s’intéresser à leur compréhension. Le but est donc de mieux cerner l’origine de ces dégradations, mieux les prédire afin de mieux les maîtriser dans le processus de dimensionnement des chaussées. C’est dans cette optique que s’inscrit la présente étude. Pour ce faire, une étude numérique est réalisée. Elle est basée sur une modélisation semi-analytique du contact. La méthode couple des solutions analytiques et des méthodes d’accélération numériques telles que la méthode du gradient conjugué (CGM) et les algorithmes de transformée de Fourier rapide (FFT). Pour atteindre une modélisation plus réaliste du contact pneu-chaussée, trois principaux aspects sont modélisés dans ce travail. Dans un premier temps, il est important de prendre en compte l’aspect multicouches de la structure de la chaussée. On utilise les coefficients de Papkovich-Neuber qui donnent des formes pour les contraintes et déplacements élastiques. En faisant une transformée de Fourier de ces dernières et en résolvant les conditions aux limites, on obtient les coefficients d’influence d’un espace semi-infini multi-couches avec un nombre quelconque de couches. Deuxièmement, la viscoélasticité est intégrée. Il s’agit de mettre en exergue le comportement viscoélastique des chaussées dû principalement à l’utilisation significative de l’asphalte dans la composition des matériaux. Afin d’intégrer ce comportement viscoélastique, une méthode de correspondance Elastique/Viscoélastique est proposée. Cette méthode impose de recalculer les coefficients d’influence à chaque pas de temps, occasionnant ainsi une augmentation des temps de calcul. Toutefois, les simulations restent très rapides par comparaison avec la méthode des Eléments Finis. Troisièmement, le contact roulant est modélisé avec la prise en compte des effets tangentiels et du coefficient de frottement statique. Le but est de pouvoir analyser les régimes transitoires (accélération, freinage, virage, etc.) pendant le roulement. Pour ce faire, il faut prendre en compte non seulement l’effort normal appliqué au contact, mais aussi le frottement à l’interface et les efforts tangentiels et éventuellement un moment de torsion. Les différents aspects de la modélisation sont validés avec des modèles de la littérature. De plus, différentes études paramétriques permettent de mieux saisir les aspects sus cités. L’application du modèle au contact pneu-chaussée a permis de montrer que dans les cas transitoires tels que l’accélération, le freinage, le virage, le dérapage, les effets tangentiels entrainent un accroissement significatif des contraintes dans la structure chaussée, surtout près de la surfaceThe purpose of this thesis has been the development of a dimensioning tool for pavement design. In order to better understand their surface degradations (mainly rutting and cracking), a modelling study is carried out. This modelling task has been performed with contact mechanics tools. Particularly, a semi-analytical model has been developed, based on Fast Fourier Transform (FFT) and Conjugate Gradient Method (CGM) algorithms. With view to achieve a more realistic modelling of the tire-pavement contact, the focus has been put on three aspects of the contact problem. Firstly, the multi-layered aspect of the pavement has been considered. Using the Papkovich-Neuber potentials, the influence coefficients have been found in the Fourier frequency domain. A numerical inversion using FFT algorithms has allowed to find the influence coefficients in the space domain. Secondly, the viscoelastic behaviour of asphaltic materials, used in roads construction, has been accounted. To this aim, an Elastic/Viscoelastic correspondence has been proposed. This correspondence imposes to recalculate the influence coefficients at every time step. These additional calculations imply an increase of the computation time; however, the simulations remain straight and fast. In addition, the proposed correspondence is exact in some cases (especially in steady-state regime); and it is an approximation in the other cases where the committed error has been shown to be marginal. Thirdly, the effects of the tangential overall forces have been integrated to the rolling contact. The goal is that the present tool can be able to simulate acceleration, braking, turnaround, etc. cases where tangential forces and/or moment are applied on the wheel in addition to the normal force (which is generally the weight of the car or truck). This tractive rolling contact has been solved between elastically dissimilar bodies submitted not only to tangential forces but also to a spinning moment. All these aspects, introduced together in the model, have allowed to perform various parametric analyses for a better grasp of their influence on general contacts. Furthermore, an application of the developed model has allowed to simulate realistic cases of rolling contact between the tire and the pavement. From examples such as acceleration, turnaround and drift, it has been proven that the tangential forces increase significantly the overall stresses
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Tamoud, Abderrahman. "Mécanique multi-échelle et multiaxiale des composites souples multicouches : application à l'annulus fibrosus humain." Electronic Thesis or Diss., Université de Lille (2018-2021), 2021. http://www.theses.fr/2021LILUN034.
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L’endommagement dans les tissus souples de l'annulus fibrosus est un phénomène multi-échelle complexe dû à un arrangement structural complexe du réseau de collagène à différentes échelles d'organisation hiérarchique. Une représentation constitutive entièrement tridimensionnelle, considérant la variation régionale de la complexité structurale, n'a pas encore été développée, pour estimer la mécanique multiaxiale de l'annulus jusqu'à la rupture. Dans la présente thèse de doctorat, un modèle, formulé dans le cadre de la mécanique non linéaire des milieux continues, est développé pour prédire l’endommagement et la rupture de l'annulus induits par la déformation sous des histoires de chargements multiaxiaux en considérant comme processus physique dépendant du temps à la fois les effets volumétriques induits chimiquement et l'accumulation de l’endommagement.Dans une première partie, un modèle basé sur la microstructure est proposé pour relier les caractéristiques structurales aux propriétés mécaniques intrinsèques et électrochimiques des tissus souples de l'annulus. Le modèle lamellaire/interlamellaire multicouche est construit en considérant les interactions effectives entre les couches adjacentes et la contrainte volumétrique induite chimiquement. La comparaison modèle/expériences démontre que l'évaluation de la réponse globale dépendante du temps implique de considérer simultanément la contrainte, le changement volumétrique et la caractéristique auxétique en relation avec les caractéristiques structurales.Dans une deuxième partie, le modèle est enrichi en considérant la structure hiérarchique des tissus souples depuis les fibrilles de collagène de taille nanométrique jusqu'aux fibres de collagène orientées de taille microscopique. Le processus stochastique d'événements progressifs d’endommagement, opérant à différentes échelles de la phase solide, est introduit pour la matrice extracellulaire, les fibres microscopiques et le réseau de fibrilles nanométriques. Les effets directionnels sur la réponse mécanique et la rupture de l’annulus sont mis en évidence en relation avec le mode de chargement externe, les caractéristiques de la structure, les événements d'endommagement et l'hydratation.Dans une troisième partie, le modèle est développé en considérant la variation régionale de l'organisation structurale complexe du réseau de collagène à différentes échelles pour prédire l’endommagement multiaxial anisotrope régional du disque intervertébral. Après identification du modèle à l'aide de lamelles simples extraites de différentes régions du disque, le caractère prédictif du modèle est vérifié pour divers modes de chargement élémentaires multiaxiaux représentatifs du mouvement de la colonne vertébrale. Les étirements dans les directions circonférentielle et radiale jusqu'à la rupture ont servi à vérifier les capacités prédictives du modèle pour les différentes régions. Les résultats du modèle sous cisaillement simple, étirement biaxial et compression en déformation plane sont également présentés et discutés.Dans une quatrième partie, un modèle de disque humain complet est construit afin d’examiner la mécanique hétérogène dans le cœur du disque. Les champs d'endommagement au sein du disque sont analysés, sous compression axiale, torsion axiale et chargements combinés, afin d’évaluer les zones où le risque de rupture est le plus élevéThe damage in annulus fibrosus soft tissues is a complex multiscale phenomenon due to a complex structural arrangement of collagen network at different scales of hierarchical organization. A fully three-dimensional constitutive representation that considers the regional variation of the structural complexity to estimate annulus multiaxial mechanics till failure has not yet been developed. In the present PhD dissertation, a model, formulated within the framework of nonlinear continuum mechanics, is developed to predict deformation-induced damage and failure of annulus under multiaxial loading histories considering as time-dependent physical process both chemical-induced volumetric effects and damage accumulation.In a first part, a microstructure-based model is proposed to connect structural features, intrinsic mechanics and electro-chemical properties of annulus soft tissues. The multi-layered lamellar/inter-lamellar annulus model is constructed by considering the effective interactions between adjacent layers and the chemical-induced volumetric strain. The model/experiments comparison demonstrates that the evaluation of the overall time-dependent response involves considering stress, volumetric change and auxetic feature simultaneously in relation to structural features.In a second part, the model is enriched by considering the hierarchical structure of the soft tissue from the nano-sized collagen fibrils to the micro-sized oriented collagen fibers. The stochastic process of progressive damage events operating at different scales of the solid phase is introduced for the extracellular matrix and the network of nano-sized fibrils/micro-sized fibers. The directional effects on annulus mechanics and failure are highlighted in relation to external loading mode, structure features, damage events and hydration.In a third part, the model is further developed by considering the regional variation of the complex structural organization of collagen network at different scales to predict the regional anisotropic multiaxial damage of the intervertebral disc. After model identification using single lamellae extracted from different disc regions, the model predictability is verified for various multiaxial elementary loading modes representative of the spine movement. The stretching along the circumferential and radial directions till failure serves to check the predictive capacities of the annulus model for the different regions. Model results under simple shear, biaxial stretching and plane-strain compression are further presented and discussed.In a fourth part, a full human disc model is constructed using the regional annulus model to examine the heterogeneous mechanics in the disc core. Damage fields in the disc are analyzed under axial compression, axial twist and combined loadings to assess the areas where the risk of failure is the highest
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Sushmita, Kumari. "Multi-layered Composite Structures for Electromagnetic Interference Shielding Applications." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5885.
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With the recent surge in the usage of electronic devices, electromagnetic interference (EMI) poses a serious threat. Unwanted electromagnetic (EM) waves not only interfere with the normal functioning of electronic components, but certain studies suggest that it is a serious threat to human health. Polymer nanocomposites serve as a promising solution for EMI shielding as they can be tuned to meet the commercial shielding requirements by incorporating suitable fillers. Moreover, polymers are lightweight, corrosion resistive, easy to process, and can be molded into complex geometries. In this dissertation, multi-layered composite structures have been fabricated and studied for EMI shielding applications. Multi-walled carbon nanotubes (CNTs) were chosen as one of the fillers owing to their electrically conducting nature. To improve the thermal conductivity and/or EM wave absorption properties, a hybrid functional filler composed of Fe3O4 decorated reduced graphene oxide (rGO) was chemically synthesized and incorporated into selected composites. Alternatively, polyurethane (PU) foam-based multi-layered structures were also fabricated to enhance the absorption-based shielding performance.
As a background study, we started with polycarbonate (PC)-based composites fabricated using the conventional melt mixing approach. PC was chosen as it has a low electrical percolation threshold for CNTs (<0.5 wt%). Total shielding effectiveness (SET) of -23 dB (1 mm thick) was obtained for PC composites with 3 wt% CNT and 10 wt% rGO-Fe3O4. A high filler loading in PC may result in either processing difficulties or poor structural properties. Therefore, PC was blended with polyvinylidene difluoride (PVDF) to improve the structural stability and also to take advantage of the double percolation effect. The selective localization of CNTs in the PC component of the PC/PVDF blend resulted in double percolation, i.e., improved bulk electrical conductivity in blend-based composites compared to single polymer composites. Despite the double percolation, the maximum SET value of -24 dB (1 mm thick) was observed with 3 wt% loading of CNTs. We further added a mutually soluble homopolymer, polymethylmethacrylate (PMMA), as a compatibilizer for the PC/PVDF immiscible blend to reduce the interfacial tension and refine the blend morphology. Despite the morphology refinement, the shielding performance declined due to the diffusion of PMMA in the individual components (PC or PVDF) and the redistribution of fillers.
In the subsequent chapters, multi-layered composite structures were opted over the conventional melt mixed composites to improve upon the shielding performance. Thin films of PVDF and PC nanocomposites were interfacially locked using a mutually miscible polymer (PMMA) to obtain a shield with enhanced structural properties and EMI shielding performance. By stacking multi-layered films one above the other, reaching an assembly thickness of ca. 0.5 mm, the maximum SET was found to be -26 dB, which is a significant improvement compared to melt mixed composites. In the next chapter, porous structures (synthesized foams and 3D printed mesh structure) were sandwiched between composite sheets of PC and PVDF with an aim to dissipate the EM signals through multiple internal reflections. PU neat and composite foams were synthesized through a polymerization reaction between 4,4’-Methylenebis(phenyl isocyanate) and polyethylene glycol. Using PU-CNT foam as an inner layer between composite sheets of PC and PVDF, a maximum SET of -39 dB (approx. 5.3 mm thick) with absorption-dominated shielding. In order to further enhance the shielding effectiveness, Ag was sputtered on the PU-foam, which resulted in the highest SET value of -50 dB in the X-band but with a significant reflection component. The results presented here begin to suggest that in-situ synthesized foam with non-uniform and dead pores enhances the shielding performance compared to non-porous structures.
Towards the end of the dissertation, PU foam was fabricated using a simpler technique of salt-leaching. By stacking freestanding CNT papers (approx. 200 µm in thickness) on both sides of lightweight PU foam, we could limit the filler content yet maximizing the absorption-based EMI shielding performance. The multi-layered structure exhibited a high SET value of -49 dB (92% absorption @ 26.5 GHz; approx. 4.6 mm thick), whereas CNT paper by itself showed a maximum SET value of -35 dB (73% absorption @ 26.5 GHz). The porous uniform PU structure enhances the absorption component of shielding due to the trapped air, adequate impedance match, and multiple internal reflections. Further, we arrived at a remarkably interesting conclusion, i.e., if the incoming wave encounters PU foam before the CNT paper (in multi-layered structure with foam and CNT paper on one side), the absorption percentage of shielding can be further enhanced (98% absorption @both 8.2 and 26.5 GHz, SET ~ -37 dB, approx. 4.4 mm thick). In such asymmetric structures, reversing the direction of the incoming EM wave can change the absorption percentage.
The results presented in this dissertation suggest the various methodology for composite fabrication and the approaches to maximize the absorption-based EMI shielding performance.
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Pykhteev, Oleg [Verfasser]. "Characterization of acoustic waves in multi-layered structures / Oleg Pykhteev." 2010. http://d-nb.info/1010249665/34.
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Huang, Wei-chu, and 黃威築. "FDTD Simulation of Elastic Waves in Cylindrical Multi-layered Structures." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/02926431066548384768.
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碩士國立中山大學
光電工程學系研究所
103
In oil field exploration, various logging devices are put into the borehole structure during and after the drilling process and also after the well cementation job to check for the hydraulic isolation between different fluid layers. Ultrasonic transducers transmit acoustic signals and produce elastic waves in the geological structure. The reflected and scattered signals are then received and processed at the same time. By the sonic and ultrasonic measuring techniques, we may understand the compositions and orientations of the geological structure and confirm the isolation quality of the cementing layer. This work is part of the four-year cooperative education research program “Modeling of borehole ultrasonic measurement” between National Sun Yat-sen University and Halliburton Far East Pte Ltd. We begin with the review of the basic physics of elasticity, including definitions of stress, strain, and stiffness tensors. For continuous media, we may apply the Hooke''s law to linearly relate the strain and the stress tensors. This is followed by Newton''s second law of motion to obtain, VS-PDEs, the first-order (in time and space), velocity-stress coupled partial differential equations for elastic wave propagation in the continuum. These control equations can be shown to be equivalent to the standard second-order vector wave equations for elastic waves and the solutions are well known to include both compressional (P) waves and shear (S) waves. We use the FDTD method to discretize the first-order VS PDEs and perform numerical simulations on the MATLAB platform. The arrangement of unknown quantities is based on the standard staggered grid (in both space and time) layout. Simulations in FDTD will be implemented on standard rectangular grid in both the Cartesian and polar coordinate systems. The calculations in the cylindrical mesh are then mapped into a rectangular grid for cross verification with the calculations done in the Cartesian mesh. By selecting the appropriate simulation parameters, simulation results in rectangular grid and in cylindrical grid are nearly identical. We plot, from these simulation results, for both types of the stress and velocity components. From these results we are able to gain clear physical pictures regarding the distribution, propagation and scattering of the elastic waves in a cylindrical multilayer structure.
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Hong-WunChen and 陳竑文. "Simulation Studies of Magnetically Controlled Wave Propagation in Semiconductor-dielectric Multi-layered Structures." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/16172991776445592882.
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碩士國立成功大學
光電科學與工程學系
103
The main idea of this investigation is to build a system to subwavelength imaging. By using transfer matrix method and the effective medium approach of the investigated components, the ability of breaking optical diffraction limitation is elucidated. Based on the derived theory results, the finite element method (FEM) based electromagnetic commercial software COMSOL is taken to prove the feasibility of this proposed device. We proposed and analyze a multilayered Semiconductor-dielectric structure for subwavelength resolution at terahertz region by controlling the magnitude of external magnetic field. Our methodology provide a way to multi-functional material, real-time subwavelength imaging, and high-density optoelectronic components with considering the effects of abnormal diffraction feature.
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Huang, Chen-Yi, and 黃琛壹. "Study and Fabrication of Optically Chemical Sensors with Multi-Layered Porous-Si Structures." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/46162692799346825615.
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碩士南台科技大學
光電工程系
98
Abstract Owing to its high sensitivity of electric, chemical and physical properties to outer environments, porous silicon (PS) is also an important material for development of chemical sensors. And in the part of multi-layered porous-Si (MLPS) structures such as Bragg reflectors and porous silicon optical micro-cavity due to it have the special optical properties. So the porous silicon (PS) becomes a major way and has been applied in design and fabrication a new type of optically chemical sensors. In this work, we demonstrated the etching current density was periodically switched between large and little during the anodic process on low resistivity of silicon substrate, which for fabrication multi-layered porous-Si (MLPS) structures on Bragg reflectors and design the particular MLPS structure on porous silicon optical micro-cavity. Then take Measure the Reflectivity and Photo-response spectra of the two structures that responding to different chemistry of organic compounds (such as methanol, acetone, ethanol and dimethyl enter). Experimental results showed that the better periodical variation of MLPS Bragg reflectors had the lower reflectivity and higher photo-responsivity of absorbed chemistry of organic compounds. The reflectivity of devices decreased while their photo-responsivity peak increased, when responding to chemical species with higher refractive index. Therefore, make use of the cross-reference for special optical sensing properties of such reflectivity, photo-responsivity, and refractive index to promote the sensitivity on sensing devices for chemical species. Porous silicon optical micro-cavity has quite special optical properties on the reflectivity spectra for organic compounds. It showed the variation in single peak value of reflectivity spectra. Moreover, the important point that we discovered the peak displacement changed on the reflectivity spectra was linear relationship for absorbed the different refractive index of chemistry of organic compounds. The peak value changed on reflectivity spectra of orange and red (during 600 nm~750 nm) in visible light wavelength. But use of the special optical properties of such structures in measurement and analysis has the very high sensitivity for different chemical species. And it has the quite high potential and application value about measurement and analysis in chemistry.
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Tzeng, Guo-Chiuan, and 曾國銓. "Characteristics of polymer flow inside a mold and quaternary structures within layers of co-extruded multi-layered film." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/9934s9.
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博士國立交通大學
機械工程系所
104
Abstract Polymer film is a major product of the polymer industry. Recent years have seen the development of multi-layer films, which are more valuable and useful than other polymer films. The quality and functionality of multi-layer films are influenced by the uniformity of the thickness of their layers, the number of interfaces within them and the structure of each layer. This investigation examines the characteristics of polymer flow inside a mold and the formation of the internal structure of layers in the film during co-extrusion. The results thus obtained will be used to improve the uniformity of layer thickness and the quality of the interfaces among the layers. Also, the effect of the limiting layer thickness on the internal structure of the layers is analyzed, and the mechanism of interfacial slip between interfaces is elucidated. An experiment in which a multi-layer film is co-extruded is carried out; the first purpose is to observe the flow of the polymer melts at the confluence in the die, and the second is to measure the variation in pressure in the die wall along the flow, and thereby evaluate the flow shear stresses. The interfacial instability is recorded using a camera through an observation window on the die wall. The flow and the stress field were analyzed during co-extrusion using POLYFLOW software. The experimental materials were observed under an optical microscope. Multilayer film co-extrusion experiments were conducted to measure the decreases in flow pressure on the mold wall in the direction of the flow to evaluate the flow shear stresses. The experimental results herein reveal that two materials with significantly different viscosities have a smooth interface. As the difference between the viscosities declines, the generation of turbulence in the interface becomes easier. A large difference between the flow rates of two co-extrusion materials induced a clear encapsulation phenomenon. In the multi-layer co-extrusion experiment, the extrusion rate was experimentally increased to increase the pressure within the flow. Based on the experimental results, when the shear stress reaches a threshold, a large number of interfaces cause interfacial slip, reducing the shear stress. Increasing the number of interfaces increases the interfacial slip. A PP/PA co-extruded film is more likely to exhibit slippage than is a PC/PMMA co-extruded film, because of the poor binding force at the PP/PA interfaces.
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Gokhale, Vaibhav V. "Design of a helmet with an advanced layered composite for energy dissipation using a multi-material compliant mechanism synthesis." Thesis, 2016. http://hdl.handle.net/1805/10910.
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Indiana University-Purdue University Indianapolis (IUPUI)Traumatic Brain Injuries (TBI) are one of the most apprehensive issues today. In recent years a lot of research has been done for reducing the risk of TBI, but no concrete solution exists yet. Helmets are one of the protective devices that are used to prevent human beings from mild TBI. For many years some kind of foam has been used in helmets for energy absorption. But, in recent years non-traditional solutions other than foam are being explored by different groups. Focus of this thesis is to develop a completely new concept of energy absorption for helmet liner by diverting the impact forces in radial directions normal to the direction of impact. This work presents a new design of an advanced layered composite (ALC) for energy dissipation through action of a 3D array of compliant mechanisms. The ALC works by diverting incoming forces in multiple radial directions and also has design provisions for reducing rotational forces. Design of compliant mechanism is optimized using multi-material topology optimization algorithm considering rigid and flexible material phases together with void. The design proposed here needs to be manufactured using the advanced polyjet printing additive manufacturing process. A general and parametric design procedure is explained which can be used to produce variants of the designs for different impact conditions and different applications. Performance of the designed ALC is examined through a benchmark example in which a comparison is made between the ALC and the traditional liner foam. An impact test is carried out in this benchmark example using dynamic Finite Element Analysis in LS DYNA. The comparison parameters under consideration are gradualness of energy absorption and peak linear force transmitted from the ALC to the body in contact with it. The design in this article is done particularly for the use in sports helmets. However, the ALC may find applications in other energy absorbing structures such as vehicle crashworthy components and protective gears. The ultimate goal of this research is to provide a novel design of energy absorbing structure which reduces the risk of head injury when the helmet is worn.
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Rammohan, B. "Design and Analysis of Multifunctional Composites for Unmanned Aerial Vehicles." Thesis, 2017. https://etd.iisc.ac.in/handle/2005/4312.
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The principal aim of this thesis is to analyse the effectiveness of multifunctional composites as intelligent structures to improve mechanical properties and activate additional non-structural features. In order to investigate these multiple aspects, a comprehensive literature review has been presented focusing on the state-of-the-art in multifunctional composites. The importance of simultaneous consideration of the nonlinearly-coupled functions in a multifunctional device is demonstrated.
The development of an analytical model for a multilayer stack subjected to temperature change is demonstrated here. Thin continuous layers of materials bonded together deform as a plate due to their differing coefficients of thermal expansion and/or shear on subjecting the bonded materials to the change in temperature. Applications of such structures can be found in the electronic industry in printed circuit boards for the study of warpage issues or in the aerospace industry as laminated thin sheets used as skin structures for load-bearing members such as wings and fuselage. In avionics, critical high-power packages (IGBT, Power FETs) include several layers of widely differing materials (Aluminum, Solder, Copper, ceramics) subjected to a wide range of cyclic temperature changes. Modeling of such structures by the application of three-dimensional finite element methods is usually time-consuming and may not accurately predict the interlaminar strains. Efforts have been made here to obtain closed-form solutions for such a multilayered stack using a set of recursive polynomial equations on subjecting the stack to temperature changes under steady-state conditions. These efforts focused on investigating laminate mechanical properties, as well as preliminary coupled electrical-structural-thermal micromechanical analyses. Several carbon reinforcing materials and potential laminate orientations were analyzed through both FEM and analytical methods to determine laminate flexural properties.
In the second phase of the work, investigation on the directionality of sound radiated from a rectangular panel, attached with masses/springs, set in a baffle, is studied. The attachment of masses/springs is done based on the receptance method. Receptance method is used to generate new mode shapes and natural frequencies of the coupled system, in terms of the old mode shapes and natural frequencies. The Rayleigh integral is then used to compute the sound field. The point mass/spring locations are arbitrary, but chosen with the objective of attaining a unique directionality. The excitation frequency to a large degree decides the sound field variations. However, the size of the masses and the locations of the masses/springs do influence the new mode shapes, and hence the sound field. The problem is more complex when the number of masses/springs are increased and/or their values are made different. The technique of receptance method is demonstrated through a steel plate with attached point masses in the first example. In the second and third examples, the present method is applied to estimate the sound field from a composite panel with attached springs and masses, respectively. The layup sequence of the composite panel considered in the examples corresponds to the multifunctional structure battery material system, used in a micro air vehicle (MAV). The demonstrated receptance method does give a reasonable estimate of the new modes.
In the third phase of this work, effects of the multifunctional composites on a few critical aeroelastic features have been investigated. The relevant modes used for the computation of flutter have been experimentally validated and mode assurance criteria (MAC) using DEW software is utilized to ascertain relevant modes. Some computational case studies related to both high-speed and low-speed unmanned aerial vehicles have been completed.
Keywords: Multifunctional Composites, Unmanned Aerial Vehicles, Finite Element Method.
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xiong, chen long, and 陳龍雄. "The study of the multi-layered structure of electrochromic devices." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/44895400358523566075.
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碩士國立勤益科技大學
機械工程系
101
This study explored manufacturing process and characteristics of electrochromic devices. Electrochromic device structure of the glass substrate, a conductive layer, a color layer, an electrolyte layer. According to the different electrolyte layer, electrochromic devices can be divided into liquid, colloidal, thin film solid-state device. This study, using a vacuum sputtering machine manufacture electrochromic device layers,and using UV spectrophotometer measure the transmittance, and compare the electrochromic coloring rate. This study was divided into three parts. In the part one study: Discoloration of the conductive layer by different ions, experimental results showed that the conductive layer of indium tin oxide thin film doping lithium-ions, sodium-ions, potassium-ions may become coloring state, indium tin oxide films exhibited yellow after doping lithium-ions, indium tin oxide films exhibited dark brown after doping sodium-ions or potassium-ions. The coloration efficiency of potassium-ions is batter than sodium-ions, and the light transmittance is low. But the use of indium tin oxide thin film electrochromic reaction of life is very poor, with only react to color three to five times. In the part two study: Lithium perchlorate propylene resin solution changed to aqueous solution of lithium perchlorate that conventional electrolyte layer used, Explore the process discoloration rate and coloring efficiency effect of thin film solid state devices doping ions in aqueous electrolyte. Experimental results show that using aqueous electrolyte in the thin film solid state devices manufacturing process can speed up the devices coloring efficiency and the coloring rate creased. In the part three study: For the color layers, using vanadium pentoxide and Tungsten trioxide make a bilayer structure for the electrochromic devices changing color with yellow, green and blue. Experimental results show that the outer coating layer of the vanadium pentoxide thin film of tungsten trioxide can be avoided the problem that pentoxide film dissolved when doping ions. This layer structure device thus prepared as a bright yellow pentoxide film and the transparent tungsten trioxide film, then the naked eye as a yellow component. For the electrochromic reaction, it can use a low voltage-1.5V to promote outer transparent tungsten oxide film is colored light blue, and the underlying thin film of vanadium pentoxide bright yellow overlap device shows the naked eye green; And then subjected to a high voltage -2.5V moved the ions into the tungsten trioxide and vanadium pentoxide thin films of tungsten trioxide films completely. Procure tungsten trioxide film is colored dark blue, while the underlying vanadium pentoxide film decolourized as transparent gray, and the device shows the naked eye blue. With this two-tier structure so as to realize the characteristics of the electrochromic device yellow, green, gray, dark blue and black multicolor conversion. The results showed that ITO conductive glass having discoloration, but still need to improve component life; while an aqueous solution of sodium ions embedded thin film solid state devices can improve the coloring rate; component in the liquid layer can effectively render color yellow blue three more colors conversion.
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Huang, Ying-Yi, and 黃庭奕. "Moisture barrier performance of SiCxNy/plasma-polymerized polymer multi-layered structure." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/10946369710761457096.
Full textAbstract:
碩士國立交通大學
材料科學與工程學系所
104
In recent years, flexible organic light emitting diode (FOLED) has emerged as the next-generation display and lighting due to their outstanding form factor and mobility. However, the reliability issues resulting from the poor moisture and oxygen barrier performance of plastic substrate is hindering the proliferation of FOLED. This prompts the academia and industry working fervently on thin-film encapsulation barrier technology to meet the goal of 10,000-hr lifetime, whose water vapor transmission rate (WVTR) shall be kept preferably below 1x10-6 g/m2-day for FOLED application. In this thesis, we successfully developed a low WVTR multi-layered structure of silicon carbonitride/plasma polymerized polymer deposited on flexible polyethylene terephthalate (PET) substrate by PECVD at low temperature (≤ 60 oC). Bis(dimethylamino)diethylsilane (BDMADES) and methyl methacrylate (MMA) are selected as the precursors for depositing inorganic and organic layers, respectively, to improve the intrinsic WVTR. This work also explored methods for reducing the pinhole density in the multi-layered barrier to further reduce WVTR. In specific, we examined the effects of deposition temperature and pressure on the defects in SiCxNy films. In addition, PPMMA layer was modified in order to achieve high-quality SiCxNy film with reduced defect in the subsequent deposition. Our study indicates that an increase in pressure can reduced the pinhole density of SiCxNy, 40%. Besides, surface modification of PPMMA prior to SiCxNy deposition leads to 60% reduction of pinhole density. Overall, the WVTR of five-pairs of SiCxNy/PPMMA thin-film barrier can be reduced down to 7.1×10-5 g/m2/day, with a lag-time of 17 hours.
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Chen, Ren-Hao, and 陳人豪. "Study of Ohmic Contact to N-type GaAs substrate with Multi-layered Gold-contained structure." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/37224798483223554963.
Full textAbstract:
碩士中原大學
電子工程研究所
97
Abstract Gallium Arsenic (GaAs) applications to devices have become increasingly critical due to the requirement for global communication industrial growth. In general, GaAs devices have the merit of the higher electric mobility than that of Si devices, fast switching speed and size of devices in miniature, therefore GaAs is used in wide range for high frequency communication. Otherwise, GaAs has anti-radiation and high reliability, so that is usually used for satellite to counteract high radiation problems in outer space. In this study, the substrate is n-type GaAs, and the ohmic contact was constructed by Ni/Au and Ni/Ge/Au. In order to find out the best annealing conditions achieving the lowest contact resistances, we intended to change annealing temperature, time duration and gas ambient. The contact resistances were measured in term of TLM and then the specific contact resistance ρc was calculated. The experimental result reveals that n-type GaAs with doping concentration ~1018cm-3 can get the lowest specific contact resistance under optimum annealing condition. In N2 ambient, Ni/Au metallurgical structure has the lowest contact resistance 1.27×10-4Ω-cm2 alloyed at 375℃ for 1min, and the contact resistance of Ni/Ge/Au is 3.13×10-6 Ω-cm2 at 350℃ for 1 min. Besides, the Ni/Au and Ni/Ge/Au has the lowest specific contact resistance for 1 min at 350℃ under H2, they are 1.37×10-5 Ω-cm2 and 1.13×10-6 Ω-cm2, respectively. The structures including germanium not only has the low specific contact resistance, but also has a more smooth surface morphology. Hence the best annealing condition has been found, the samples will be put onto the thermal pad to measure thermal variation under 30℃, 60℃, 90℃ and 120℃ to observe the thermal effect on specific contact resistance. And discuss thermal stability of metal contact fabricated at 250℃ in the H2 environment.
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Chou, Gia-Wen, and 周嘉文. "Disign of a multi-layered optical sensor for ship structural stress and strain condition diagnosis." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/85144620909162246692.
Full textAbstract:
碩士國防大學中正理工學院
造船工程研究所
96
Simultaneous recording of shear and pressure is a critical issue for studying the causes of the fatigue damage in ship structure. In order to obtain a meaningful stress distribution around the “hot point” of ship structure, a novel optical sensor for pressure and shear sensing was designed and tested. The sensing principle is based on the bending loss of optical fibers. When external forces applied to the sensor, the optical fibers will bend and cause the light to escape from the fibers. The amount of light attenuation depends on the amount of fiber bending. The sensor consists of two sets of cross-meshed optical fibers embedded in an elastomeric polymer, which lay in parallel and separated by an additional elastomeric layer. Pressure is measured based on the force induced light loss from the two affected crossing fibers. Shear was measured based on the relative position changes on these pressure points between the two fiber mesh layers. Two different grid layouts were developed and tested. One is the aligned layout and the other one is the offset layout. The results show that the offset layout is more sensitive to shear loading than the aligned layout. To verify the practicality of the optical sensor under various loading patterns at multiple sensing points, an artificial neural network (ANN) algorithm was used as a recognition tool. A two stage back-propagation neural network (NNet) was used for training and testing. The first stage was designed for identifying its loading pattern and the second stage was designed for recognizing load direction. Light intensities measured from the sensing fibers are the inputs of the NNet. Testing results show that NNet is an effective recognition tool for post-processing the sensor measurements.
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Hsieh, Chen-I., and 謝禎益. "Study of multi-layered copper-contained ohmic contact structure on n-type GaAs and its application." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/30891747517558550045.
Full textAbstract:
碩士中原大學
電子工程研究所
95
The multi-layered Ge / Cu / Ni / Au metal structure is investigated through the TLM method and through surface morphology inspection to study the feasibility of forming an n-type ohmic contact for n-GaAs material and its application in InGaP / GaAs DJ solar cell in this report. Experimental results indicate that enough thickness Cu is essential for obtaining the lower specific contact resistance ρc and keeping the annealing temperature low; while too much Ni and Ge thickness could degrade the ohmic contact quality but having no apparent effect on the annealing temperature for obtaining the best ρc. Additionally, an optimum metallurgical structure of Ge (30nm) / Cu (120nm) / Ni (40nm) / Au (50nm) with a rather low ρc ∼5.84×10−6Ωcm2 can be obtained after annealing at 435℃ for 1 min. Furthermore, this ohmic metal structure Ge / Cu / Ni / Au is deposited for n-type ohmic contact on InGaP / GaAs DJ solar cell. Measurements of the open circuit voltage (Voc), short circuit current (Isc), fill factor (FF) and conversion efficiency (η) are approximately equal to those of device using conventional Ni / Ge / Au / Ni / Au metal contact. Moreover it is also indicated that the solar cell with Ge / Cu / Ni / Au metal contact structure has good thermal stability.
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Liao, Yi-Tse, and 廖藝澤. "Structural and Luminescent Properties of Sputter Deposited Silicon Oxynitride Films and Multi-layered Silicon Oxynitride/Silicon Stack." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/2r64g3.
Full textAbstract:
碩士國立臺灣科技大學
材料科學與工程系
99
Silicon oxynitride (SiOxNy) and multi-layered silicon oxynitride/silicon structures (SiON/Si) with different nitrogen and oxygen concentrations were fabricated by reactive magnetron sputtering deposition followed by thermal annealing in high vacuum environment. According to the x-ray photoelectron spectroscopy analyses, the binding energies of Si 2p3/2, N 1s and O 1s shift with deposition condition of SiON. Four tetrahedral phases such as Si─N4, Si─N3O, Si─O3N, and Si─O4 are possibly present, corresponding to the four bonding units Si3N4, Si2ON2, Si6O9N2 , SiO2. Si3N4 is believed to be the origin of nitrogen dangling bonds, and silicon oxynitride structures like Si2ON2 and Si6O9N2 are the origin of O─Si─N bonds. In combination with analyses of Raman spectroscopy and high resolution transmission electron microscopy, we demonstrate that there is no silicon clusters in the SiON films. Strong room temperature photoluminescence, excited by He-Cd 325 nm laser, from defect– related states was observed in about 400 nm, 510 nm and 780 nm. It is found that blue emission peak arises from the nitrogen dangling bonds which dominate in the samples with relatively higher nitrogen concentration; the green emission peak originates from the luminescent center of O─Si─N bonds which dominate in the higher oxygen concentration ones; peaks at 780 nm is probably from the recombination between N 2p and O 2p. For multi-layered SiON/Si films, white photolumine- scence was observed due to the additional luminescence at ~610 nm from quantum dots formed in the silicon layers of the film. Visible electroluminescence was obtained from SiOxNy and multi-layered SiON/Si films on p-type silicon substrate in a ITO/SiON/Si Wafer/Al structure. The I-V behavior is indicative of space charge-limited current, and the EL was possibly attributed to the recombination of carriers through the luminescent center in the SiON layer. The PL and EL were present only in annealed samples, and the emissions are similar from same samples which suggests the recombination centers from PL and EL are the same.
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Garcia, Gabriel S. "Concepts for mechanistic-empirical design procedure for extended life hot mix asphalt pavements with a multi-layered structure /." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3290238.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7509. Adviser: Marshall R. Thompson. Includes bibliographical references (leaves 204-212) Available on microfilm from Pro Quest Information and Learning.
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Yang, Kai 1982. "FFT and multigrid accelerated integral equation solvers for multi-scale electromagnetic analysis in complex backgrounds." Thesis, 2014. http://hdl.handle.net/2152/26036.
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Novel integral-equation methods for efficiently solving electromagnetic problems that involve more than a single length scale of interest in complex backgrounds are presented. Such multi-scale electromagnetic problems arise because of the interplay of two distinct factors: the structure under study and the background medium. Both can contain material properties (wavelengths/skin depths) and geometrical features at different length scales, which gives rise to four types of multi-scale problems: (1) twoscale, (2) multi-scale structure, (3) multi-scale background, and (4) multi-scale-squared problems, where a single-scale structure resides in a different single-scale background, a multi-scale structure resides in a single-scale background, a single-scale structure resides in a multi-scale background, and a multi-scale structure resides in a multi-scale background, respectively. Electromagnetic problems can be further categorized in terms of the relative values of the length scales that characterize the structure and the background medium as (a) high-frequency, (b) low-frequency, and (c) mixed-frequency problems, where the wavelengths/skin depths in the background medium, the structure’s geometrical features or internal wavelengths/skin depths, and a combination of these three factors dictate the field variations on/in the structure, respectively. This dissertation presents several problems arising from geophysical exploration and microwave chemistry that demonstrate the different types of multi-scale problems encountered in electromagnetic analysis and the computational challenges they pose. It also presents novel frequency-domain integral-equation methods with proper Green function kernels for solving these multi-scale problems. These methods avoid meshing the background medium and finding fields in an extended computational domain outside the structure, thereby resolving important complications encountered in type 3 and 4 multi-scale problems that limit alternative methods. Nevertheless, they have been of limited practical use because of their high computational costs and because most of the existing ‘fast integral-equation algorithms’ are not applicable to complex Green function kernels. This dissertation introduces novel FFT, multigrid, and FFT-truncated multigrid algorithms that reduce the computational costs of frequency-domain integral-equation methods for complex backgrounds and enable the solution of unprecedented type 3 and 4 multi-scale problems. The proposed algorithms are formulated in detail, their computational costs are analyzed theoretically, and their features are demonstrated by solving benchmark and challenging multi-scale problems.text
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WANG, CHIA-TIEN, and 王嘉田. "Implementation of the Layered Desktop Structure with Virtual Disk Technology: A multi-OS Environment Management and Rapid Deployment System." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/91375491151056870179.
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碩士國立中正大學
雲端計算與物聯網數位學習碩士在職專班
104
Deploying Operation System (OS) and its applications on a large number of machines, either personal computers or handheld devices, is a routine but pesky task for IT staffs in K-12 schools. This research work developed a management system for multi-OS environment for IT staffs in K-12 schools to deploy and maintain desktop environment package on large number of machines in their campus. A Layered Desktop Structure (LDS) with Virtual Disk Technology (VHD) has been implemented to simplify the deployment process. The LDS partitioned the desktop environment into several logical and isolated virtual disk files which usually include the OS layer, the application layer and the data layer. The proposed solution is easy to dynamically manage x86 desktops for diverse demands from different computer classes or compute-intensive task deployments. Important features of our proposed solution include (1) A boot-menu for desktop environment and management utility; (2) Provide easy and elastic OS and software deploy method; (3) Support fast recovery for a ruined desktop environment; (4) Provide rapid maintenance service to support daily learning activities; (5) Support heterogeneous hardware platforms (desktop/notebook/netbook PC). The proposed solution has been tested and deployed on more than six thousands of machines in K-12 schools in Taiwan. The experimental results showed that the solution is able to reduce the manpower cost and effectively serving the needs from the teaching sites.
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Chang, Li-Chun, and 張立群. "Study of Multi-layered Silver-contained Ohmic Contact Structure on N-type GaAs and Its Application to Solar Cell." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/68309901931697354165.
Full textAbstract:
碩士中原大學
電子工程研究所
96
Abstract In this study, we proposed a gold-free metallization ohmic contact structure composed of nickel (Ni), germanium (Ge), and silver (Ag) deposited on n-GaAs. We investigated ohmic contact through the TLM method and calculated the specific contact resistance. Experimental results indicate that the Ge / Ag series metallurgical structure have an ohmic contact behavior, and a rather low specific contact resistance ρc ~ 4.81×10-6Ωcm2 is attained from Ge (20nm) / Ag (150nm) after annealing at 425℃ for 1 minute. Then we deposited Ni layer before Ge and Ag layers, the Ni / Ge / Ag series metallurgical structure also have an ohmic contact behavior, too, and an optimum metallurgical structure Ni (10nm) / Ge (20nm) / Ag (150nm) with the lowest specific contact resistance ρc ~ 4.15×10-6Ωcm2 can be obtained after annealing at 425℃ for 1 minute. However, with the increasing Ge thickness, the characteristics of ohmic contact would be more difficult to be displayed; for the increasing thickness of Ni layer, the best annealing temperature is increased, and the quality of ohmic contact is dropping. In addition, the surface morphology of Ni (10nm) / Ge (20nm) / Ag (150nm) annealed at 425℃ for 1 min is as smoother as that of Ge (20nm) / Ag (150nm) by incorporating with an additional nickel (10nm). We also studied the thermal stability of the as mentioned before metallurgical structures and conventional Ni / Ge / Au / Ni / Au metallurgical structure under environmental temperature 200℃ in H2 ambient. From the experimental results, it is found that Ni (10nm) / Ge (20nm) / Ag (150nm) metal-contact has better thermal stability than the conventional Ni / Ge / Au / Ni / Au metal contact. After the TLM experiment, the optimum metallurgical structure Ni (10nm) / Ge (20nm) / Ag (150nm) is applied to n-GaAs ohmic contact that the front electrode of the InGaP / GaAs / Ge triple-junction (TJ) solar cells with three annealing temperatures. The current-volatge (I-V) characteristics are measured under one-sun and multi-suns at room temperature. By the one-sun measurement results, we get the better solar cell performance such as conversion efficiency (EFF), fill factor (FF), maximum output power (Pmax) at the annealing temperature 425℃. Furthermore, by the multi-suns measurement results, the conversion efficiency (η) were all improved, and the fill factor (FF) still kept at a relative good values ~0.82 in these three annealing temperatures.
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Kumar, Kabbinahithlu Gautham, and 高山柯. "Highly efficient and transparent MoO3/Ag/WO3 top anode multi-layered structure for inverted transparent organic light emitting diodes." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/k7s9cz.
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碩士明志科技大學
電子工程系碩士班
106
An alternative design of a highly transparent anode for bi-directional emission green-phosphorescent organic light-emitting diodes (OLEDs) has been investigated. The scope of this study was to improve the bi-directional luminance and out-coupling efficiency in terms of transmittance and external quantum efficiency (EQE) of OLEDs used for display while keeping the current density versus voltage (J-V) characteristic unchanged. An n-type doped wide bandgap organic electron injection layer (EIL), caesium carbonate-doped 4,7-diphenyl-1,10-phenanthroline (Cs2CO3: BPhen), was incorporated between the indium tin oxide (ITO) cathode and an active layer of OLEDs. All the layers in this small-molecule based OLED device were fabricated by vacuum deposition technique. An emission ratio of 1:1.1 between top and bottom electrode was achieved with a maximum top luminance of 6600 cd/m2 and bottom luminance of 7245 cd/m2. The result shows that it is possible to achieve high efficiency by inserting suitable EIL at the ITO/organic interface. Results reveal the high optical transmittance (above 90%) of multilayered MAW and average overall device transmittance of 80% in the visible region (400-700 nm). Using this optimized structure including both electrodes, inverted transparent OLEDs showed total EQE of 20.5%, current efficiency and power efficiency of 67 cd/A and 62 lm/W respectively.
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Huang, Chih-Ling, and 黃芷翎. "Novel nerve regeneration conduits made by different ratios of poly (L-lactide-co-glycolide) forming with porous and multi-layered structure." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/05049606043726968542.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
93
Nerve bridging is suture a biomaterial-made conduit and to overpass the damaged nerve end to end with microsurgery. Peripheral nerve could be bridged between the proximal nerve and the distal stump to restore the function. Nerve conduits could eliminate tension at the healing site and induce the regeneration of axons. Nerve conduits also could permit neurobiological recovery to enhance neural regeneration and stop cells and their secretions from obstructing neural regeneration. In this study, we used poly L-latcide (PLLA), poly DL-latcide-co-glycolide 75:25 (PLGA7525) and poly DL-latcide-co-glycolide 50:50 (PLGA5050) during citric acid inducing ammonium bicarbonate gas forming process to form porous polymer film, and rolled the porous polymer film to make nerve conduits with pores and multi-layered. Electron Spectroscopy for Chemical Analyzer (ESCA) and Attenuated Total Reflectance – Fourier-Transform Infrared Spectrometer (ATR-FTIR) were employed for determining elements’ functionabilities and chemical compounds. Charge Coupled Device camera (CCD camera) and Scanning Electron Microscope (SEM) were employed for macroscopic and microscopic morphologies and structural observation. Differential Scanning Calorimetry (DSC) was employed for measuring glass-transition temperature (Tg). Nano-indentation system was employed for measuring elastic modulus and hardness. Biodegradation and water absorption ratios were measured to analyze their chemical properties and SEM was employed for microscopic morphology of the tested nerve conduit. Experiment results demonstrated that during citric acid inducing ammonium bicarbonate gas forming process, no salts (ammonium bicarbonate) remained, while Tg of PLGA5050 was lower than human body temperature. The porous structures of PLGA5050 conduit were dissolved into a condensed morphology after 28 testing days, while the material was completely degraded after 56 testing days. The degradation of PLGA7525 conduit was relatively slow, while the porous structures slightly changed their shapes after 56 testing days. Using citric acid inducing ammonium bicarbonate gas forming and unique rolling process, PLLA is relatively suitable to make multi-layered nerve conduits, which provide highly porous structures with many round openings. In addition, the porous structures with channeling characteristic can be preserved to 56 testing days.