This study concentrates on two of the main processes involved in the fabrication of electrostatic valve assembly, thick resist photolithography and wet chemical etching of a polyamide film. The electrostatic valve has different orifice diameters of 25, 50, 75 and 100 µm. These orifice holes are to be etched in the silicon wafer with deep reactive ion etching. The photolithography process is developed to build a mask of 15 µm thick resist pattern on silicon wafer. This photo layer acts as a mask for deep reactive ion etching. Wet chemical etching process is developed to etch kapton polyamide film. This etched film is used as a stand off, gap between two electrodes of the electrostatic valve assembly. The criterion is to develop the processed using standard industry tools. Pre post etch effects, such as, surface roughness, etching pattern, critical dimensions on the samples are measured with Veeco profilometer.

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No description available.

No description available.

The present report aims to show the development process of a liquid level sensing system for the use within the propellant tanks of a launch vehicle. Whereas many recent launchers use discrete level sensing systems to indicate the amount of fuel on defined spots like fill-stop and engine cut-off, in this report a continuous capacitance based sensor probe is described. An accurate knowledge of the propellant level can serve as input for the throttling of the propellant valves to account for changes in the oxidizer-fuel ratio and therefore helps optimising the operation of the rocket engine. Furthermore, the more precise the amount of fuel is known, the less unused propellant mass will remain allowing a cost and mass optimisation for each mission. Additionally to the increased vehicle performance, the sensor designs described aim to have comparably low mass and cost. At the beginning of the report, an overview of different level measuring techniques is given before going into the special conditions and requirements regarding launch vehicles. Afterwards, the design and testing with RP-1 and LN2 of two different sensor probes using a capacitive measuring principle is described and compared to analytical calculations and numerical simulations using COMSOL Multiphysics. At the end, design suggestions for a flight probe and possible improvements for a higher reliability are given. All tested sensor designs show an accuracy of a few millimetres when tested within a settled, non-sloshing fluid. However, the theoretical models show a substantial deviation to the test data. / Föreliggande rapport syftar att visa utvecklingsprocessen av ett vätskenivåavkänningssystem för användningen i drivmedelstankarna i en bärraket. Medan många nya bärraketer använder diskreta nivåavkänningssytem för att ange mängden bränsle på definierade händelser som textit tankstopp och textit motor avstängning, beskrivs i denna rapport en kontinuerlig kapacitansbaserad sensor. En exakt kunskap om bränslenivån kan fungera som inmatning för strypningen av bränsleventilerna för att ta hänsyn till förändringar i förhållandet mellan oxidationsmedel och bränsle förhållandet. Detta hjälper därför till att optimera driften av raketmotorn. Dessutom, ju exaktare mängden bränsle är känd, desto mindre oanvänd bränsle återstår, vilket möjliggör en kostnads- och massoptimiering för varje uppdrag. Förutom den ökade fordonsprestandan syftar de beskrivna sensordesignerna till att ha jämförelsevis låg massa och kostnad. I början av rapporten ges en översikt över olika nivåmättekniker innan de speciella förhållandena och kraven för bärraketer berörs. Därefter beskrivs design och testning med med RP-1 och LN2 av två olika sensorer som använder en kapacitiv mätprincip och jämförs med analytiska beräkningar och numeriska simuleringar med COMSOL Multiphysics. I slutet ges designförslag för en flygprob och möjliga förbättringar för en högre tillförlitlighet. Alla testade sensorkonstruktioner visar en noggrannhet på några milimeter när de testas med en stilla, icke-plaskande vätska. De teoretiska modellerna visar dock en väsentlig avvikelse från testdatan.

Polymer matrix composites (PMC's) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymer's properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilledâ ¦) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymer's mechanical behavior within and across the property transition regions. In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMC's in end-loaded bendingâ ¦). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMC's in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches. / Ph. D.

<p>The fabrication of zone plate lenses that are used for focusing X-rays relies on nanofabrication techniques such as e-beam lithography, reactive ion etching, and electroplating. The circular grating-like zone plate pattern can have a smallest half-period, a so-called zone width, of down to 20 nm while it also needs to have a height that is 5 to 10 times the zone width to have good diffraction efficiency. This high aspect ratio structuring is a very challenging field of nanofabrication.</p><p>This diploma project has focused on improving the process step of fabricating the electroplating mold by cryo-cooling the polymer during the reactive ion etching with O₂. The low temperature causes passivation of the sidewalls of the mold during etching which results in a more ideal rectangular profile of the high aspect ratio plating mold.</p><p>By etching at -100 °C, structures with highly vertical sidewalls and no undercut were realized. The experiments showed that there is a tradeoff between the anisotropy of the zone profile and the formation rate of polymer residue, so-called RIE grass. Through a proper choice of process parameters the grass could be completely removed without introducing any undercut.</p> / QC 20100414

The landscape of consumer electronics has drastically changed over the last decade. Technological advances have led to the development of portable media devices, such as the iPod, smart phones and laptops. This has been achieved primarily through miniaturisation and using materials such as Lithium and Indium Tin Oxide (ITO) to increase energy density in batteries and as transparent electrodes for light emitting displays respectively. However, ten years on there are now new consumer demands, which are dictating the direction of research and new products are under constant development. Graphene is a promising next-generation material that was discovered in 2004. It is composed of a two-dimensional lattice made only from carbon. The atoms are arranged in a two atom basis hexagonal crystal structure which forms a fundamental building block of all sp2 hybrid forms of carbon. The production of large area graphene has a high cost, due to the long growth times and the high temperatures required. This is relevant as graphene is not viable compared to other transparent conductors which are produced on industrial scales for a fraction of the cost of graphene growth. Furthermore, graphene has a high intrinsic resistivity (2KW/_) which is three orders of magnitude greater than the current industry standard ITO. This limits the size of the electrodes as there is dissipation of energy across the electrode leading to inefficiency. Furthermore a potential drop occurs across the electrode leading to a non-uniform light emission when the electrode is used in a light emitting display. I investigate alternative methods of large area graphene growth with the aim of reducing the manufacturing costs, while maintaining the quality required for graphene human interface devices. Building on this I develop new fabrication methods for the production of large-area graphene devices which are flexible and transparent and show the first all graphene touch sensor. Focusing on the reducing the high resistivity of graphene using FeCl3 intercalation, while maintaining high optical transmission, I show low resistivity achieved using this process for microscopic graphene flakes, large-area graphene grown on silicon carbide and large-area graphene grown by CVD. Furthermore, I explore the stability of FeCl3 intercalated graphene and a process to transfer a material to arbitrary flexible substrates.

Die thermodynamischen Eigenschaften von Flüssighelium erfordern einen hohen technischen Aufwand zu dessen Lagerung und Transfer. Aufgrund der extrem niedrigen Normalsiedetemperatur von 4,2 K ist die Verflüssigung des unter Normbedingungen gasförmigen Heliums sehr energieintensiv. Darüber hinaus besitzt Helium eine sehr niedrige Verdampfungsenthalpie, weshalb bereits geringe Wärmeeinträge signifikante Verdampfungsverluste verursachen. Infolge der räumlichen Trennung von Heliumverflüssigungsanlagen und Verbrauchern ist ein Flüssigheliumtransfer in der Regel unvermeidlich. Beim Transfervorgang durch Wärmeeintrag und Druckverluste generiertes Heliumkaltgas muss erneut dem energieaufwändigen Verflüssigungsprozess zugeführt werden, bevor es als Kältemittel verwendet werden kann. Zur Etablierung eines verlustarmen Flüssigheliumtransfers mit einflutigen flexiblen Transferleitungen sind daher die Verdampfungsverluste im Rahmen der thermohydraulischen Optimierung zu reduzieren. Die Optimierung erfolgt dabei durch die Kopplung von systematischen Messungen mit thermohydraulischen Berechnungen. Untersuchungen mit instrumentierten Versuchstransferleitungen erfolgen an einem an der Heliumverflüssigungsanlage der Technischen Universität Dresden neu eingerichteten Versuchsstand. Dabei stellt sich heraus, dass der Gesamtdruckverlust vorwiegend durch das im flexiblen Abschnitt eingesetzte Wellrohr verursacht wird. Mittels eines gesonderten Messaufbaus werden verschiedene Wellrohrtypen hinsichtlich der resultierenden Reibungsdruckverluste untersucht und eine verlustarme Wellrohrgeometrie identifiziert. Neben den Druckverlusten wird auch der Wärmeeintrag durch Modifikationen des Isolationsaufbaus reduziert. Im Zuge der thermohydraulischen Optimierung vermindern sich die Verdampfungsverluste, wodurch die pro Zeiteinheit in der Transportkanne deponierte Flüssigheliummenge zunimmt. Zusätzliche Messungen während des Stillstands der Transferleitung liefern Rückschlüsse auf das Verhalten der Transferleitung, wenn kein Flüssighelium transferiert wird. Im Stillstand neigen die betrachteten Transferleitungsgeometrien zu thermisch angetriebenen Druckschwingungen, sogenannten thermoakustischen Oszillationen. Diese beeinflussen die Betriebssicherheit und die Lagergüte des stationären Speichers negativ, weshalb geeignete Methoden zur Dämpfung der thermoakustischen Oszillationen vorgeschlagen werden.

Wide-bandgap (WBG) semiconductor materials such as silicon carbide (SiC) and gallium-nitride (GaN) allow higher voltage ratings, lower on-state voltage drops, higher switching frequencies, and higher maximum temperatures. All these advantages make them an attractive choice when high-power density and high-efficiency converters are targeted. Two different gate-driver designs for SiC power devices are presented. First, a dual-function gate-driver for a power module populated with SiC junction field-effect transistors that finds a trade-off between fast switching speeds and a low oscillative performance has been presented and experimentally verified. Second, a gate-driver for SiC metal-oxide semiconductor field-effect transistors with a short-circuit protection scheme that is able to protect the converter against short-circuit conditions without compromising the switching performance during normal operation is presented and experimentally validated. The benefits and issues of using parallel-connection as the design strategy for high-efficiency and high-power converters have been presented. In order to evaluate parallel connection, a 312 kVA three-phase SiC inverter with an efficiency of 99.3 % has been designed, built, and experimentally verified. If parallel connection is chosen as design direction, an undesired trade-off between reliability and efficiency is introduced. A reliability analysis has been performed, which has shown that the gate-source voltage stress determines the reliability of the entire system. Decreasing the positive gate-source voltage could increase the reliability without significantly affecting the efficiency. If high-temperature applications are considered, relatively little attention has been paid to passive components for harsh environments. This thesis also addresses high-temperature operation. The high-temperature performance of two different designs of inductors have been tested up to 600_C. Finally, a GaN power field-effect transistor was characterized down to cryogenic temperatures. An 85 % reduction of the on-state resistance was measured at −195_C. Finally, an experimental evaluation of a 1 kW singlephase inverter at low temperatures was performed. A 33 % reduction in losses compared to room temperature was achieved at rated power. / <p>QC 20160922</p>