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Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.

The research reported in this dissertation focuses on the development of optimization tools for the design of subsystems in a modern aircraft power distribution system. The baseline power distribution system is built around a 270V DC bus. One of the distinguishing features of this power distribution system is the presence of regenerative power from the electrically driven flight control actuators and structurally integrated smart actuators back to the DC bus. The key electrical components of the power distribution system are bidirectional switching power converters, which convert, control and condition electrical power between the sources and the loads. The dissertation is divided into three parts. Part I deals with the formulation of an optimization problem for a sample system consisting of a regulated DC-DC buck converter preceded by an input filter. The individual subsystems are optimized first followed by the integrated optimization of the sample system. It is shown that the integrated optimization provides better results than that obtained by integrating the individually optimized systems. Part II presents a detailed study of piezoelectric actuators. This study includes modeling, optimization of the drive amplifier and the development of a current control law for piezoelectric actuators coupled to a simple mechanical structure. Linear and nonlinear methods to study subsystem interaction and stability are studied in Part III. A multivariable impedance ratio criterion applicable to three phase systems is proposed. Bifurcation methods are used to obtain global stability characteristics of interconnected systems. The application of a nonlinear design methodology, widely used in power systems, to incrementally improve the robustness of a system to Hopf bifurcation instability is discussed. / Ph. D.

Magnetische Formgedächtnislegierungen (MSM-Legierungen) weisen im Vergleich zu anderen Festkörperwandlern und konventionellen elektromagnetischen Wandlerprinzipien unikale Kopplungseigenschaften auf. Dies motiviert ihre Anwendung in kompakten und schnellschaltenden Antrieben. Aufgrund der Kompliziertheit ihres Kopplungsverhaltens ist jedoch ein modellbasierter Entwurf unumgänglich. Die vorliegende Arbeit widmet sich der Beschreibung einer Unterklasse von MSM-Antrieben mit eisenbehafteten Magnetkreisen und engen Luftspalten durch eine Kombination von Messung und Modell. Ziel ist dabei die Beantwortung anwendungsrelevanter Fragestellungen im Antriebsentwurf. Die Grundlage dafür bildet die heuristische Definition eines auf verallgemeinerten Kirchhoffschen Netzwerken (Netzwerkmodellen) basierenden Ersatzmodells des MSM-Elements samt umgebendem Luftspalt. Die das Verhalten des Ersatzmodells beschreibenden magnetischen Größen werden durch ein neuartiges und im Rahmen der Arbeit entwickeltes Messverfahren ermittelt. Ein Prüfstand setzt dieses Messverfahren um und ermöglicht eine simultane magnetische und magnetomechanische Charakterisierung von MSM-Elementen unter Kraft- oder Wegvorgabe. Eine empirische Validierung der gemessenen Zusammenhänge, auch anhand thermodynamischer Gesichtspunkte, weist die Plausibilität der das Ersatzmodell beschreibenden Zusammenhänge nach. Diese Ergebnisse motivieren die Entwicklung eines Netzwerkmodells, das die hysteresebehaftete magnetomechanische Kopplung innerhalb des Ersatzmodells thermodynamisch korrekt berücksichtigt. Mithilfe des Modells gelingt es, das experimentell bestimmte integrale magnetomechanische Verhalten des MSM-Elements samt umgebendem Luftspalt in wesentlichen Aspekten vorherzusagen. / Magnetic shape memory (MSM) alloys are considered promising active materials for compact electromagnetic drives due to their strong magneto-mechanical coupling. However, the latter is associated with a strong nonlinearity and a distinct hysteresis making a model-based design indispensable. The present work describes the behavior of a subclass of MSM drives with iron-core and small air gaps by means of a combination of model and experiment. Heuristically, an equivalent lumped-element model considering the MSM element and the surrounding air gap is proposed. An associated novel magnetic measurement procedure determines the quantities describing the behavior of this equivalent model. A test setup implements the measurement procedure and allows for a simultaneous magnetic and magneto-mechanical characterization either under constant load or under constant displacement. An empiric validation, also with regard to thermodynamic aspects, indicates the plausibility of the collected data describing the simplified equivalent model. These results motivate the development of a novel lumped-element model considering the hysteretic magneto-mechanical coupling of the equivalent model in a thermodynamically consistent way. Its validation by means of various magneto-mechanical experiments shows that the model is able to predict the essential magnetic and magneto-mechanical behavior of the MSM element and the surrounding air gap with sufficient accuracy, making it appropriate for system design.

<p>With the advent of increasingly complex radio systems at higher frequencies and the slowing of traditional CMOS process scaling with power concerns, there has been an increased focus on integration, architectural, and material innovations as a continued path forward in MEMS and logic. This work presents the first comprehensive experimental study of resonant body transistors in a commercial 14nm FinFET process, demonstrating differential radio frequency transduction as a function of transistor biasing through electrostatic, piezoresistive, and threshold voltage modulation. The impact of device design changes on unreleased resonator performance are further explored, highlighting the importance of phononic confinement in achieving an f*Q product of 8.2*10¹¹ at 11.73 GHz. Also shown are initial efforts towards the understanding of coupled oscillator architectures and a perovskite nickelate material system. Finally, development of resonators based on two-dimensional materials, whose scale is particularly attractive for high-frequency nano-mechanical resonators and acoustic devices, is discussed. Experiments towards dry transfer of tellurene flakes using geometries printed via two photon polymerization are presented along with optimization of a fabrication process for gated RF devices, presenting new opportunities for high-frequency electro-mechanical interactions in this topological material. </p>

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Quadruped robots can traverse a multitude of terrains with greater ease when compared to wheeled robots. Traditional rigid quadruped robots possess severe limitations as they lack structural compliance. Most of the existing soft quadruped robots are tethered and are actuated using pneumatics, which is a low grade energy source and lacks viability for long endurance robots. The work in this thesis proposes the development of a continuum actuator driven quadruped robot which can provide compliance while being un-tethered and electro-mechanically driven. In this work, continuum actuators are developed using mostly 3D printed parts. Additionally, the closed loop control of continuum actuators for walking is developed. Linear Quadratic Regulator (LQR) and pole placement based methods for controller synthesis were evaluated and LQR was determined to be better when minimizing the actuator effort and deviation from set-point. These continuum actuators are composed together to form a quadruped. Gait analyses on the quadruped were conducted and legs of the quadruped were able to trace the gaits for walking and galloping. / Fyrfotarobotar kan lättare korsa en mängd olika terränger jämfört med hjulrobotar. Traditionella styva fyrfotarobotar har kraftiga begränsningar då de saknar strukturell följsamhet. De flesta befintliga mjuka fyrbenta robotar är kopplade till en eller flera kablar och drivs av pneumatik, vilket är en lågkvalitativ energikälla och lämpar sig inte för robotar med lång uthållighet. Arbetet i denna avhandling föreslår utvecklingen av en continuum ställdonsdriven fyrfotarobot, som ger följsamhet samtidigt som den ¨ar frånkopplad och elektromekaniskt driven. I detta arbete framställs continuum ställdon med mestadels 3D-printade delar. Dessutom utvecklas dessa ställdons slutna kontrolloop för gång. Linjärkvadratisk regulator (LQR) och metoder baserade på polplacering utvärderades för styrsyntes, och det fastställdes att LQR presterade bättre när man minimerar ställdonets ansträngning samt avvikelse från referensvärde. Continuum ställdon sammansattes för att bilda en fyrbent robot. Gånganalyser utfördes på roboten och dess ben kunde följa gång- och galopprörelser.

Quadrupedal robots are mobile robots with four limbs. Compared with other mobile robots, quadrupedal robots are more capable of moving in complex environment. Specifically, softquadrupedal robots have the limbs that are flexible and more compliant with the environmentthan that of rigid quadrupedal robots. This project is based on a previous work at KTH where a soft quadrupedal robot prototype was built. The first part of this project is to build a test rig, analyze the dynamics of the 3D printed soft continuum actuators and choose one configuration toachieve the best dynamics. The second part of this project is to build a soft quadrupedal robotand analyze the standing and walking performance. The mechanical and electrical structure ofthe robot are re-designed to reduce the weight. Furthermore, gait analyses are conducted toenable the robot to walk. Cost of transport is calculated to compare the efficiency of differentgaits. / Mobila robotar som har fyra lemmar kallas fyrbenta robotar. Jämfört med andra mobila robotarär fyrbenta robotar mer kapabla att röra sig i komplexa miljöer. Särskild de mjuka fyrbentarobotar, vars flexibla lemmar är mer kompatibla med miljön än dem av stela fyrbenta robotar. Det här projektet är baserat på ett tidigare arbete på KTH där prototypen av en mjuk fyrbentrobot byggdes. Den första delen av detta projekt är att bygga en provrigg, analysera dynamikenav det 3D-skrivna mjuka kontinuumställdon och välja den konfigurationen som har bästadynamiken. Den andra delen av detta projekt är att bygga en mjuk fyrbent robot och analyseradess stå- och gångprestation. Den mekaniska och elektriska strukturen av roboten designades omför att minska vikten. Vidare är gångs analyser genomförda för att möjliggöra robotens gång. Cost of transport (COT) är uträknat för att jämföra olika gångs effektivitet.

The transition to more environmentally sustainable transports, as well as rising fuel prices create a demand for efficient means of transportation. Liftable axles have shown potential to save fuel and reduces tire wear on heavy vehicles. This thesis proposes a simulation environment and a control method for the electronically controlled air suspension system on a four axle truck that enables axle lifting. The goal of the work is to propose a control method that fulfills certain safety criteria and is robust to disturbances introduced by an external un-modeled controller. A simulation environment is proposed, based upon two different physical models of the suspension system. The first model offers simplicity for the initial tuning of the controller and the second model serves as a platform for more realistic testing of the controller before the final vehicle test. The results from the vehicle tests show that the proposed controller is able to regulate the pressure in the suspension bellows to the desired load distribution between the axles of the vehicle, while the vehicle is maintaining a certain height above ground. The vehicle test showed that it was difficult to read the correct pressure in the suspension bellows when the valves controlling the airflow in and out of the suspension bellow were open. A method for compensating the error when the valves are open is proposed. / Övergången till hållbara och miljövänliga transporter samt stigande bränslepriser skapar en efterfrågan av mer effektiva transportmedel. Lyftbara axlar har visats medföra minskad bränsleförbrukning och däckslitage. Denna uppsats föreslår en simuleringsmiljö samt en metod för reglering av det elektroniskt styrda luftfjädringssystemet på en fyraxlig lastbil som möjliggör lyftning av en axel. Målet med arbetet är att föreslå en metod för reglering av systemet som uppfyller en rad säkerhetskriterier och är robust för störningar introducerade av en extern, icke-modellerad styrenhet. Den föreslagna simuleringsmiljön är baserad på två olika fysiska modeller av fjädringssystemet. Den första modellen karakteriseras av dess enkelhet och används för inledande testning och justering av regulatorn. Den andra modellen används för mer realistisk testning av regulatorn innan det avslutande fordonstestet. Resultatet från fordonstesterna visar att den föreslagna regulatorn kan reglera trycket i luftbälgen till den önskade lastfördelningen mellan axlarna på fordonet medan dess höjd bibehålls. Under fordonstestet konstaterades att det inte gick att avläsa det korrekta trycket i luftbälgen när ventilerna som styr luftflödet till och från luftbälgen var öppna. En metod för att kompensera felet som uppstår när ventilerna är öppna föreslås.

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