23 research outputs found

    Predicting the drawing conditions for microstructured optical fiber fabrication

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    The efficient and accurate fabrication of Microstructured optical fibers (MOFs) requires a practical understanding of the ‘draw process’ beyond what is achievable by trial and error, which requires the ability to predict the experimental drawing parameters needed to produce the desired final geometry. Our results show that the Fitt et al. fluid-mechanics model for describing the draw process of a single axisymmetric capillary fiber provides practical insights when applied to more complex multi-hole symmetric and asymmetric MOF geometries. By establishing a method to relate the multi-hole MOF geometry to a capillary and understanding how material temperature varies with the draw tower temperature profile, it was found that analytical equations given by the Fitt model could be used to predict the parameters necessary for the chosen structure.We show how this model provides a practical framework that contributes to the efficient and accurate fabrication of the desired MOF geometries by predicting suitable fiber draw conditions.Roman Kostecki, Heike Ebendorff-Heidepriem, Stephen C. Warren-Smith, and Tanya M. Monr

    Corrosion Detection: A Fibre Optic Approach

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    Corrosion is a multi-billion dollar problem faced by industry. High acquisition costs associated with modern military and civilian aircraft coupled with tighter budgets has resulted in the need for greater utilisation of existing aircraft eets. With advancing aircraft age there is increased possibility that protective coatings will break down or be damaged, resulting in exposure of the base material to the environment and an increased possibility of corrosion. Corrosion is most difficult to detect in inaccessible metallic structures within aircraft. Monitoring these areas requires a sensor capable of spatially resolved detection of corrosion (distributed measurements), so that the location of the detected corrosion can be determined. Optical fibre based sensors are inherently suited to distributed sensing and are typically in the order of only a few hundred microns in diameter making them very lightweight and suitable for embedding in otherwise inaccessible corrosion-prone areas. This thesis describes the development of an optical fibre based corrosion sensing element. Transition of exposed-core microstructured optical fibres from soft glass to silica is shown to provide a platform for optical fibre sensors requiring long term and/or harsh environmental applications while providing real time analysis anywhere along the fibres length. The portion of light guided outside of the glass core, often described as the `evanescent field,' is affected by the refractive index and absorption characteristics of the surrounding medium. Functionalising this core with chemosensors sensitive to corrosion by-products, turns the light guiding fibre into a corrosion sensing element, with which insitu kinetic measurements of accelerated corrosion in simulated aluminium aircraft joints is demonstrated. This provides a fibre optic approach for detection of corrosion inside the hidden part of structures and opens up new opportunities for distributed optical fibre chemical sensing with a capacity for long-term application in harsh environments.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

    Emerging Microstructured Fibers for Linear and Nonlinear Optical Applications in the Mid-Infrared and Terahertz Spectrum

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    Les régions spectrales des ondes térahertz (THz) et de l'infrarouge moyen (mIR) représentent les frontières immédiates nous séparant du but d'exploiter le spectre électromagnétique dans son intégralité pour les applications technologiques du futur. La bande spectrale de l'infrarouge moyen couvre les longueurs d’ondes entre 2 et 20 microns du spectre infrarouge. Diverses applications tirant profit du mIR sont envisagées dans de nombreux domaines d intér ts tels: spectroscopie imagerie infrarouge chirurgie laser et bio-diagnostic Malgré les nombreux avantages immédiats pouvant tre tirés des applications du spectre mIR, sa pleine exploitation demeure ce jour limitée en raison d’une part par le manque de sources laser mIR couvrant une large portion de ce domaine spectral En effet la majorité des sources cohérentes mIR actuellement disponibles oscillateurs paramétriques optiques lasers cascades quantiques lasers électrons libres sont discr tes et restreignent ainsi les applications une seule longueur d’onde spécifique la fois. Il existe actuellement une forte demande au sein de l'industrie et la communauté scientifique pour la création d’une source lumineuse cohérente large bande spectrale émettant dans le mIR, et sous une forme compacte. Le premier sujet de recherche de cette thèse se rapporte au design de nouvelles fibres hautement nonlinéaires (FHNL) pour leur utilisation dans la génération de lumière mIR (e.g. génération d'un supercontinuum), et au sein de dispositifs de conversion en longueurs d'onde mIR basés sur des effets optiques nonlinéaires. À cet effet, l'efficacité de génération/conversion de la lumière mIR dépend intimement du contrôle des propriétés optiques linéaires et nonlinéaires du guide d'onde employé dans le système. Au cours de mes travaux, j'ai étudié différents designs de guides d'ondes microstructurés (ou nanostructurés) hautement nonlinéaires et possédant un potentiel pour des applications à impact concret. Plus particulièrement, nous avons démontré deux nouveaux types de FHNL: la fibre optique nanostructurée hybride en chalcogénures-métal qui supporte un mode plasmonique permettant un confinement du champ à des dimensions profondément sous-longueur d'ondes, ainsi que la fibre microporeuse en verres de chalcogénures offrant des possibilités étendues pour le contrôle de la dispersion chromatique dans les fibres optiques nonlinéaires. Par ailleurs, des simulations numériques basées sur l'équation de Schrodinger nonlinéaire, et assumant cette dernière FHNL comme guide d'onde, ont été effectuées et ont démontré leur potentiel pour la génération d'un large supercontinuum mIR dans----------Abstract The terahertz (THz) and middle-infrared spectrum (mIR) represent the next frontiers in the goal of harnessing the whole electromagnetic spectrum in future technological applications. The middle-infrared spectral band covers the wavelengths between 2 and 20 microns in the infrared. A myriad of applications that take advantage of the mIR spectrum are envisioned in several fields of interest such as: spectroscopy, infrared imagery, laser surgery and bio-diagnostic. Despite the numerous immediate benefits that may be reaped from applications of mIR technology, its full exploitation remains limited by the lack of bright and coherent optical sources of mIR light. In fact, the majority of current mIR coherent sources (optical parametric oscillators, quantum cascade lasers, free electron lasers) are discrete and thus restrict applications to a single specific wavelength at a time. Thus there is presently a strong demand within the industrial and academic communities for the creation of a broad bandwidth coherent mIR light source in a compact form factor. The first research topic of my thesis was to design novel highly-nonlinear fibers (HNLFs) to be used in mIR light generation (e.g. supercontinuum generation) and mIR wavelength conversion schemes based on nonlinear optical effects. The efficiency of mIR light generation/conversion depends intimately on the precise control of the linear and nonlinear optical properties of the waveguide used in the optical setup. During the course of this work, we investigated various designs of both microstructured and nanostructured highly-nonlinear waveguides with great potential for end-user applications. In particular, we demonstrated two novel types of HNLFs: the hybrid chalcogenide-metal nanostructured optical fiber that supports a plasmonic mode enabling deep-subwavelength field confinement capabilities, and the chalcogenide microporous fiber that provides extensive design freedom for engineering the chromatic dispersion of nonlinear fibers. Furthermore, simulations of the nonlinear Schrodinger equation, assuming the latter type of HLNF, were performed and showed the potential for generating a broad mIR supercontinuum inside a chalcogenide microporous fiber seeded at long wavelengths (i.e. 10.5 μm) using short picosecond pulses. Furthermore, the study of the hybrid chalcogenide-metal nanostructured optical fiber demonstrated subwavelength-size optical mode confinement beyond the classical diffraction limit. This feat was made possible by harnessing surface plasmon polaritons guided by th

    Mathematical modelling of unsteady tube stretching with internal channel pressurisation for fabricating electrospray ionisation emitters

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    Nanoelectrospray ionisation (nESI) is a useful technology for assessing the chemical composition of various liquid samples using mass spectrometry (MS). Signi cant e orts have been made in the design of nESI emitters, as their shape and geometry are critical to the electrospray performance and subsequent MS detection. In the actual manufacturing of these emitters through the heat and draw process, the desired geometry cannot, at present, be achieved. In particular, the inner channel reduces in size, which is not desirable. To improve the sensitivity of biological and chemical mass spectrometry and avoid clogging of the tip, a small near-uniform bore of 10 - 20 m is desirable with the external wall tapering over a length of around 5mm from 75 - 150 m in radius to a sharp end with a radius around 8 - 15 m. Through mathematical modelling, we demonstrate, for the rst time, the feasibility of producing such emitters using the heat and draw process with the addition of pressure in the channel to prevent any reduction in size. In this thesis, we consider the unsteady problem of heating and pulling of an axisymmetric cylindrical glass tube, using asymptotic methods to exploit the slenderness of the tube and over-pressure applied within the inner channel, to form tapers with a near uniform bore and small wall thickness at the tip. This is an unsteady extensional ow problem. As the glass temperature increases, the viscosity reduces until the central heated region extends and thins rapidly to yield an hour-glass shape. During stretching, the cross-sectional geometry will also deform under the e ects of surface tension and applied pressure, with the pressure counteracting the closure of the channel by surface tension and, perhaps, further expanding it. When cooled and cut transversely at the centre, two identical tapered capillaries are obtained. In this thesis, we assume molten glass is a Newtonian uid, and develop coupled ow and energy models to examine in detail the in uence of the process parameters on the geometry, namely the pulling force, pressure, temperature, and surface tension. The use of an over-pressure in the channel, to counteract the reduction in its size as the crosssectional area decreases due to pulling and the channel closes due to surface tension, is of particular interest. The model and solution method described in this thesis enable determination of a pulling force, channel over-pressure, and draw time to achieve tapers with the desired internal diameter and wall thickness at the very tip from a given tubular bre for a temperature dependent viscosity.Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 202

    Chemical, mechanical, and thermal control of substrate-bound carbon nanotube growth

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 323-357).Carbon nanotubes (CNTs) are long molecules having exceptional properties, including several times the strength of steel piano wire at one fourth the density, at least five times the thermal conductivity of pure copper, and high electrical conductivity and current-carrying capacity. This thesis presents methods of CNT synthesis by atmospheric-pressure thermal chemical vapor deposition (CVD), where effective choice of the catalyst composition and processing conditions enables growth of tangled single-wall CNTs or structures of aligned multi-wall CNTs, on bare silicon, microstructured silicon, and ceramic fibers. Applying mechanical pressure during growth controls the structure of a CNT film while causing significant defects in the CNTs. This mechanochemisty approach is used to "grow-mold" CNTs into 3D-shaped microforms. A new reactor apparatus featuring a resistively-heated suspended platform enables rapid ( 100 °C/s) temperature control and versatile in situ characterization, including laser measurement of CNT film growth kinetics, and imaging of stress-induced film cracking. By thermally pre-treating the reactant mixture before it reaches the substrate platform, aligned CNTs are grown to 3 mm length in just 15 minutes.(cont.) A microchannel array is created for combinatorial flow studies of nanomaterials growth, having velocity range and resolution far exceeding those of conventional furnaces. A detailed design methodology considers compressible slip flows within the microchannels and flow leaks across the array, and the devices are fabricated by KOH etching of silicon. Initial experiments with this system demonstrate chemically-driven transitions in CNT yield and morphology along the microchannels, and flow-directed alignment of isolated CNTs and CNT strands. Applications of aligned CNTs in reinforced composites and electromechanical probes are enabled by the CNT synthesis technologies presented here, and show significant initial promise through collaborative research projects. Overall, controlling the packing density and matrix reinforcement of aligned CNTs gives material attributes spanning from those of energy-absorbing foams to stiff solids; however, significant increases in CNT length, growth rate, and packing density must be achieved to realize macroscopic fibers and films having the properties of individual CNTs. New machines can be created for studying the limiting aspects of growth reactions, for exploring new reaction regimes, and for producing exceptionally long nanostructures, looking ahead to fabrication of CNT-based materials in a continuous and industrially-scalable fashion.by Anastasios John Hart.Ph.D

    Designing Sorbent-Containing Electrospun Fibers For Dilute Chemical Separations

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    abstract: An urgent need for developing new chemical separations that address the capture of dilute impurities from fluid streams are needed. These separations include the capture of carbon dioxide from the atmosphere, impurities from drinking water, and toxins from blood streams. A challenge is presented when capturing these impurities because the energy cost for processing the bulk fluid stream to capture trace contaminants is too great using traditional thermal separations. The development of sorbents that may capture these contaminants passively has been emphasized in academic research for some time, producing many designer materials including metal-organic frameworks (MOFs) and polymeric resins. Scaffolds must be developed to effectively anchor these materials in a passing fluid stream. In this work, two design techniques are presented for anchoring these sorbents in electrospun fiber scaffolds. The first technique involves imbedding sorbent particles inside the fibers: forming particle-embedded fibers. It is demonstrated that particles will spontaneously coat themselves in the fibers at dilute loadings, but at higher loadings some get trapped on the fiber surface. A mathematical model is used to show that when these particles are embedded, the polymeric coating provided by the fibers may be designed to increase the kinetic selectivity and/or stability of the embedded sorbents. Two proof-of-concept studies are performed to validate this model including the increased selectivity of carbon dioxide over nitrogen when the MOF ZIF-8 is embedded in a poly(ethylene oxide) and Matrimid polymer blend; and that increased hydrothermal stability is realized when the water-sensitive MOF HKUST-1 is embedded in polystyrene fibers relative to pure HKUST-1 powder. The second technique involves the creation of a pore network throughout the fiber to increase accessibility of embedded sorbent particles. It is demonstrated that the removal of a blended highly soluble polymer additive from the spun particle-containing fibers leaves a pore network behind without removing the embedded sorbent. The increased accessibility of embedded sorbents is validated by embedding a known direct air capture sorbent in porous electrospun fibers, and demonstrating that they have the fastest kinetic uptake of any direct air capture sorbent reported in literature to date, along with over 90% sorbent accessibility.Dissertation/ThesisDoctoral Dissertation Chemical Engineering 201
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