This study establishes an adhesive bonding strategy for the micro-assembly of optical components using UV-curable adhesives. The focus is on factors influencing adhesive shrinkage and alignment accuracy. Key findings reveal that higher UV intensity reduces both volumetric and linear shrinkage, while curing from below the substrate minimizes horizontal shifts on the to-be bonded optical components, eliminating the need for horizontal offset adjustments. The study highlights how variations in the distance between the substrate and component affect vertical shrinkage displacements and stresses the importance of precise adhesive volume control to enhance accurate shrinkage prediction. The developed shrinkage prediction model forecasts sub-micrometer accurate vertical component shrinkage compensations, validated through comprehensive parameter testing. To advance research toward more accurate shrinkage predictions and a deeper understanding of adhesive shrinkage behavior, future studies propose integrating multi-angle observation systems and expanding parameter testing. These efforts aim to refine prediction models and validate strategies in real-world applications, thereby enhancing the reliability and precision of optical systems across industrial and scientific domains.

The use of geometric anti-springs (GASs) in MEMS accelerometers can not only boost the sensitivity through the static balancing effect, it also introduces the capability to tune the stiffness post-manufacturing by adjusting the balancing force. This paper addresses the challenge of mechanically fine-tuning the stiffness to create the potential for compensating thermal drift of bias (TDB), whereas previous methods focused on doing so electrostatically. Due to the large effect of TDB on integration errors, creating this new method for compensation could help open up the way to more accurate inertial navigation by high-precision MEMS. As the basis of our research we used an existing accelerometer from Innoseis Sensor Technologies (version G6). Based on a theoretical analysis of the TDB, requirements were formulated and a design was developed through a combination of pseudo-rigid body and finite element modelling. By building a macro-scale prototype, we were able to validate our models. It can therefore be concluded that our design provides 8 additional compression steps ranging between 50 and 54 nm based on the model predictions. This proof-of-concept demonstrates to be a new tool in the design of future accelerometers with GASs.

Life at low-Reynolds numbers regime is intriguing. Single motile bacteria are known to exhibit erratic behaviour; they swim in what is known as a random walk, alternating between periods of swimming straight and abrupt moments of re-orientation. Yet in dense populations, cells of E.coli have been reported to exhibit weak synchronization and self-organize into collective oscillatory motion patterns. However, the origin of this rhythmic behaviour remains largely unknown. Here, we present a method of inducing self-sustained oscillations over minute timescales in single E.coli cells by trapping them in circular microcavities. By engineering the size of these microwells, we show that the velocity of single E.coli can be tuned between speeds ranging from a few to 20 um/s. Furthermore, we show that by connecting the microwells via on-chip channels, E.coli tend to coordinate their motion through hydrodynamic interaction and exhibit collective dynamics. Using analytical modeling, we extract the coupling strength and design the channels to mediate synchronized oscillation between two bacterial oscillators. Our work not only advances our understanding of the collective dynamics of swarming bacteria but also provides the first evidence for single-cell bacterial oscillators, paving the way to using micro-organism-inspired oscillations in applications as varied as antibiotic screening, scientific computing and micro-swimmers.

Small satellites require efficient propulsion systems for attitude and orbit control. This thesis focuses on the development and characterization of two distinct types of micro-resistojet thrusters, namely Vaporizing Liquid Micro-resistojet (VLM) and Low Pressure Micro-resistojet (LPM). Both concepts are developed at TU Delft and are designed to use water as a propellant, conforming to launch-safety, simplicity, and cost-effectiveness criteria.
In VLM, liquid water is vaporized and accelerated through a convergent-divergent nozzle. In contrast, LPM operates by reducing water vapor pressure to below 300 Pa and then accelerating it through expansion slots under a rarefied flow regime. Both types of thrusters are built on Micro-Electro-Mechanical Systems (MEMS) chips to accommodate the size constraints of nano- and pico-satellites.
The thesis introduces refined designs for both VLM and LPM thrusters. Specifically, the VLM design features an optimized nozzle shape and improved inlet flow, while the redesigned LPM assembly is more space-efficient. These modifications increase the thrust-to-size ratio for both thruster types.
The thesis presents a fabrication process for these thrusters, employing an anodic bonded silicon-glass wafer stack with a capped microfluidic channel. Fabrication was executed at the EKL lab, using a simplified manufacturing process that is detailed within the report.
Post-fabrication, the thrusters underwent mechanical and electrical characterization. The results indicate incremental improvements in both design performance and manufacturability. The new VLM design yielded a 15% increase in thrust efficiency, while the new LPM assembly reduced the occupied volume by 30%.

Proteins play a key role in many biological processes and are thus useful indicators of health and disease states. Since the size of proteins is few hundred nanometers, it is necessary to explore new techniques to manipulate and 'read' them. This thesis aims to identify and build a platform that enables sub-micron bead manipulation, which will be used to actively deliver the biomolecules attached to the beads to the single-molecule sensor. During this process, accurate positioning, speed control, and multiplexing of the beads need to be solved to give high-resolution and high-throughput sequencing capabilities. We identify surface acoustics wave (SAW) devices as powerful tools to achieve both beads transport and massively parallel manipulation. Our hypothesis is that we can increase the efficiency and precision of bead capture and manipulation by using SAW devices combined with a microcavity layer. In this master thesis, we fabricate the SAW device with an average 2 $\mu m$ thick film, and there are cavity arrays on the film. In addition, we investigate the performance of trapping sub-micron objects during the actuation. Further more, we discuss few challenges found through the experiments and provide possible solutions for them. At last, this thesis is concluded by discussing the work been done and providing suggestions for future experiments.

Biosensing properties like mass, density and stiffness on a single cell level can help diagnose diseases. Mass sensing of cells and subcellular components is typically performed with resonant microstructures. Recently such microstructures were fabricated using an emerging 3D printing technique called two-photon polymerization (2PP) contrary to conventional lithography-based fabrication. The suspended microchannel resonator (SMR) is such a resonant microstructure with an embedded fluidic channel for buoyant mass sensing, which has not yet been fabricated using 2PP. This work aims to 3D print an SMR with a sufficient mass resolution to detect the buoyant mass of E. Coli bacteria (175 fg in water). It was realized by first characterizing the damping in 3D printed polymer microbeam resonators for a better understanding of dominating damping sources. Followed by maximizing their quality factor and fabricating a prototype 3D-printed SMR. The characterized devices set a record-breaking standard for damping of polymer microbeam resonators: Cantilevers and bridges approached quality factors of 1000 and tensile stressed narrow bridges achieved a quality factor of 1819. These polymer resonators were dominated by bulk friction damping, but still had a mass resolution advantage over similar silicon-based devices when working in lower quality factor (Q < 1000) conditions, due to the low mass density of the polymer. Subsequently, prototypes of the suspended microchannel resonator were fabricated with multi-scale 3D printing containing a plug-and-play connection to fluidics and measurement equipment. Their theoretical mass resolution was estimated to be ≤ 60 fg, which is sensitive enough to detect E. Coli bacteria and compete with conventional fabricated SMRs. This paves the path towards actual biosensing 3D printed SMRs with the capabilities of lithography-based fabricated devices but with additional design and fabrication flexibility.

In connection with growing in applications of nanoparticles in various industrial sectors such as cosmetics and pharmaceuticals, the demand for in-line identification and characterization of nanoparticles suspended in fluids has increased. In addition to that, nanoparticles in general and nanoplastics in particular, can easily contaminate air and water resources, resulting in human health risks. Among available techniques, suspended microchannel resonators can respond to the characterization demands in terms of mass detection and concentration of nanoparticles in fluids. This technique is based on changes in resonance frequency of the suspended microchannel due to flowing of nanoparticles through the suspended hollow cantilever. In this project we aimed to characterise TUDelft made suspended microchannel resonators in terms of mass limit detection and speed of detection. We found that the lowest resolved mass can be detected by the second bending mode. This was 0.11 fg and0.38 fg using an empty and a water-filled resonator respectively, for a system bandwidth of 1000 Hz that corresponds to a system settling time of 0.37 ms. We also managed to measure a buoyant mass of 21.2 fg which is an equivalent gold nanoparticle of 130 nm in diameter, during one of the attempts to detect suspended gold nanoparticles in deionized water.

Microglia, the resident macrophages of the central nervous system, are key players in neuroinflammation and neurodegenerative diseases, such as Alzheimer’s and Parkinson’s. These cells represent promising cellular targets for therapeutic intervention, therefore a detailed cellular biological knowledge of microglia is of paramount importance. Current microglia in vitro cell culture models are limited in their ability to recapitulate in vivo microglia in terms of gene expression and cell morphology. There is growing evidence that mimicking the cellular environment of microglia in the central nervous system will contribute to a more physiologically accurate culture model. Three-dimensional geometries, and physical and biochemical cues similar to the brain’s extracellular matrix, are necessary to create a 3D biomimetic in vitro environment, as microglia cells can sense these environmental cues through mechanosensing. In this thesis, the effect of two-photon polymerized 2.5D and 3D microstructures on microglia morphology and phenotype was studied through quantitative and qualitative cell analysis. Also, an attempt was made to create in vitro ramified microglia that resemble in vivo microglia from a morphological point of view, by con-trolling the effective shear modulus through dimensional optimization of compliant micro-and nanopillars. It was found that culturing microglia especially on nanopillars enabled an increase of the ramified pheno-type and a more complex (i.e. more ramifications) cell morphology as compared to microglia cultured onflat fused silica substrates. Furthermore, we report that microglia cultured on 3D structures exhibit similarphenotypes observed in the 2D and 2.5D cultures, and were more resemblingin vivomicroglia in terms of3D cell morphology.

In the last few years organ-on-chip (OoC) has been emerging as a new method for more reliable research to screen the effects of new drugs on the body. This is a novel technology mimicking the in vivo environment of tissue cells, making it a more suitable candidate for experimentation than traditional 2D cell cultures. However, in order to ensure smooth and swift implementation of this technique, some issues must be addressed first. One of these issues concerns perfusion: most OoC devices require external equipment to provide the necessary dynamic flow that makes the OoC unique, so that cells experience continuous fluid shear and are perfused sufficiently. In this thesis a model of an on-chip electro-polymeric pump is designed for application on an OoC. From a background study the design aims are defined: a membrane actuated pump with a nozzle-diffuser channel providing pump action. The membrane is made from ionic polymer-metal composite (IPMC), a material that deforms under electric current which is produced at TU Delft with the intention to use it in OoC applications. Its low voltage operating range and its biocompatibility make it an excellent candidate for this. Furthermore, the nozzle-diffuser elements avoid the need for moving elements inside the channel, instead providing pump action based on a pressure gradient over the nozzle elements. Finally, three design aims are defined, being: high flowrate, high flow pulse and low flow rate and pulse applications, corresponding to various needs in the OoC field. A base model is designed using COMSOL Multiphysics software, using similar devices described in literature. The model consists of a combination of solid mechanics (for membrane movement), fluid mechanics (for flow movement) and a fluid-structure interaction module to combine the two. This model is then tested for a range of parameters, first independently and later in pairs. General conclusions drawn from these simulations include: - Between the membrane displacement and -frequency (which can both be varied after fabrication), the membrane displacement magnitude affects the output more significantly than actuation frequency - The membrane width is positively correlated with flow rate output and pulse amplitude - The channel depth is positively correlated with flow rate output, but only if the membrane displacement scales along with it - A long slender nozzle yields lower flow output than a short, squat nozzle - The results from this model are consistent with nozzle-diffuser theory, stating that nozzle resistance and membrane movement affect the flow most significantly. This leads to three designs according to the three application wishes expressed earlier. The pump is designed such that it can be manufactured on a silicon wafer using electronics cleanroom equipment. The combination with the process developed for IPMC provides a novel pumping mechanism that has the potential to fully integrate an important aspect of an OoC on-chip, greatly increasing user friendliness and allowing for wider implementation of this technology.

Cell behavior in vitro can be regulated by mechanical stimulation. Cytostretch is an Organ-on-Chip (OOC) platform that allows cyclic stretching tissue in culture. Its pneumatic actuation can hinder it from microfluidic systems integration. A dielectric elastomer actuator (DEA) was developed and fabricated in this thesis for Cytostretch as an alternative actuation method. The DEA consists of a suspended polymer membrane sandwiched between electrodes, which can induce out-of-plane motion when a voltage is applied. The functionality of the design was proved in numerical analysis. A complete process flow was developed and partly implemented for the wafer-scale microfabrication of this innovative actuator. The top electrodes of the device were fabricated by depositing and patterning titanium nitride with stress buffering layers. The quality of the electrodes was examined and wrinkles were found at corners of certain etching patterns. The angle of the corner and spacing between corners were proposed to be two factors influencing the wrinkle formation. This work paves the way to the successful integration of DEAs for mechanical stimulation of cell tissues within OOC platforms.

Patients with orthopaedic implants often experience implant-associated infections (IAI), one of the most prominent causes for implant failure. IAIs are caused by pathogens adhering to the implant surface. One method to prevent IAIs is through the use of surface topography modifications. Cellular behaviour has been shown to be influenced by substrate surface topographies. Ideally, a topography that can simultaneously kill bacteria and promote osseointegration is desirable. In previous research, proved-to-be-bactericidal nanopillars of ~180 nm in height and ~80 nm in diameter were fabricated at 170 nm interspace, resulting in a bactericidal efficiency of 36 ± 5% for Staphylococcus aureus (S. aureus). The current research aimed to enhance this bactericidal efficiency by producing nanopatterns with different interspace distances and introducing disorder, while keeping the same nanopillar dimensions. The patterns have been produced by using electron beam induced deposition (EBID) at 100, 170, 300 and 500 nm interspacing. A disordered version of the 170, 300 and 500 nm samples was included with 45, 110 and 210 nm disorder distance, respectively. In order to keep the nanopillar dimensions consistent, EBID parameters were systematically optimised. The nanopatterns were interfaced with S. aureus cells and the bactericidal efficiencies were determined by counting the number of healthy, deformed and dead bacterial cells. For the ordered 100, 170, 300 and 500 nm interspace nanopatterns, bactericidal efficiencies of 62.3 ± 23.1%, 45.0 ± 31.4%, 8.6 ± 4.2% and 3.7 ± 2.3% were found, respectively. For the disordered 170, 300 and 500 nm interspace nanopatterns, bactericidal efficiencies of 45.9 ± 29.2%, 14.7 ± 7.2% and 12.7 ± 9.8% were found, respectively. These results showed a significantly higher bactericidal effect on lower-interspace nanopatterns. Disordered nanopatterns showed only slightly higher bactericidal efficiencies when compared to the ordered nanopatterns. This data indicated that bactericidal efficiencies could be increased relative to the previous nanopattern design. The findings of this research aid in developing antibacterial nanopatterns that are capable of killing gram-positive bacteria and support the path to prevention of IAIs.

The Nobel Prize in Chemistry in 2017 went to the development of cryo-electron microscopy, which contributed to the discovery of new cells and viruses, the diagnosis of unknown diseases, the mapping of human genomes and the manufacturing of semiconductors. Cryo Correlative light and electron microscopy (Cryo-CLEM), is the combination of using fluorescence microscopy and cryo-electron microscopy to image cryo-immobilized bio-samples. These samples (at a temperature lower than −165ᵒC), require critical conditions in preparation and preservation to prevent contamination and heating which have a negative influence on the imaging results. In the current sample transfer workflow, almost 90% of the samples transferred end up being wasted due to the unideal protection and transfer gap. Therefore, an integrated high-vacuum sample transfer system which fits the interfaces of CLEM devices and actively protects the samples from heating and contamination in transfer has been designed to conquer the problems, ensure better imaging results, and increase the process yield. COMSOL simulations on its thermal and mechanical behaviors have been carried out to theoretically verify and iterate the design. The new transfer system provides a cheaper, faster, easier, more contamination-free, more temperature-stable, more user-friendly workflow that can increase the yield of sample transfer from 10% to 90%.

In the past few decades, there has been a growing demand for low-cost disposable sensors to be utilized in hazardous and toxic environments such as high temperature and chemically aggressive environments, which can lead to irreversible damage to the sensor. Moreover, by cost reduction, they become more attractive for utilization in developing countries, where the research of new biomedical technologies has been restricted due to a decentralized healthcare system, lack of infrastructure and shortage of investment. This research focuses on developing a low-cost, disposable and easy to use mass sensor utilizing diamagnetic levitation. Diamagnetic levitation is the only stable form of levitation at room temperature and does not require external sources of energy, feedback loops or cooling for stable levitation. It is a low cost, easy to use, disposable sensor that makes it suitable for potential point-of-care applications. The sensor consists of a pyrolytic graphite plate that levitates above a checkerboard arrangement of permanent magnets with alternating magnetization. The system is actuated using electromagnetic excitation and the material properties of the sample are extracted by conducting a multi-modal analysis of the resonance frequencies and mode shapes; measured using a laser Doppler vibrometer (LDV). An opto-electronic phase lock loop utilizing the LDV is used to bring the levitating pyrolytic graphite into sustained mechanical oscillation controlled by a PID controller. The experimental mass sensitivity is measured by analysing the frequency shift associated with the placement of glass beads. The frequency stability is measured by computing the Allan deviation and the experimental precision of mass sensor is then computed. The results show that the precision of a diamagnetically levitated resonant mass sensors decreases with the decrease of the size of the levitating oscillator. The precision of a levitating oscillator of side length 2mm and thickness 0.08mm is found to be 14.4pg at a gate time of 0.1s for an instantaneous change in frequency.

Inkjet printing offers an additive manufacturing method for the production of thin films. A variety of inkjet printed materials can be printed, including conductive and electroactive materials. Existing inkjet printed ferroelectric polymer actuators all utilize silver conductive layers and P(VDF-TrFE) for the electroactive layer. This thesis will describe the manufacture of P(VDF-TrFE-CTFE) actuators with inkjet printed carbon black electrodes. A conductive carbon black film is printed on a resin coated PET substrate to form the actuator bottom electrode. P(VDF-TrFE-CTFE) is spin coated on top of the electrode to form the active ferroelectric material, before finally another carbon black layer is printed on top to produce the top electrode. To validate the choice of electrode material, a selection of conductive inks are tested to compare conductivity and quality of deposition when printed with a commercial printer. The ease of printing and post processing is also compared to determine what ink can be used as an electrode material whilst requiring the fewest and quickest manufacturing steps. From this a model is produced to determine the maximum actuator operation frequency depending on electrode material. Produced actuators achieve 206 microns steady state deflections at 300 V and 3 mm at resonance. This shows an 89.4% improvement in strain per volt compared to similar inkjet manufactured P(VDF-TrFE) actuators in literature.

The research of advanced material such as Carbon Nanotubes (CNT) has attracted considerable attention in achieving high efficiency and good performance in the electrical and electronic system during the last few decades. In this research project, the designs and fabrication process for microswitches which are made by carbon nanotubes have been investigated. Much efforts have been done for optimization in growing micrometer length carbon nanotubes, horizontalization of carbon nanotube bundles, and mechanical properties controlled by silicon carbide (SiC) coating. A modeling design is developed to show the feasibility of the electrostatic drive and the electromagnetic drive for the on and off states of the switch. Besides this, the phenomenon that the substrate topology can give a significant influence on carbon nanotube bundles’ alignment direction during its growth by temperature no uniform distribution was observed and proved by the simulation and the measurement. In order to compensate and put right the aligned direction, horizontalization methods supplied by disposing photoresists have been explored and successfully showed the practicability to change the bundles' direction after deposition. Also, optical and electrical characteristics have been done to show the good performance of this device. The future work can relate to optimizing the process parameters to improve the throughput and repeatability. Also, device dimensions can be optimized to get higher electrical performance. An additional test in reliability can also help with checking its robustness under extreme working conditions. More interestingly, substrate topology design can be explored to implement self-controlled carbon nanotube bundles alignment.

Atherosclerotic plaque rupture is the main cause of acute myocardial infarction and stroke, the two leading causes of death worldwide. Rupture of plaque tissue is a mechanical event, where plaque stress or strain locally exceeds its strength. Biomechanical studies agree with histopathological findings that a large lipid pool and thin fibrous cap overlying the lipid pool increase the likelihood of rupture, by showing increased plaque stresses for these geometries. Another plaque morphological feature that is frequently encountered is calcification. However, its role in the vulnerability of plaques to rupture is not fully understood, and biomechanical modeling studies do not agree on the effect of calcifications on plaque stress. These studies used isotropic material properties for the anisotropic and collagen rich plaque tissue, and generally focused on the effect of calcification on lumen stress or cap stress. However, histopathological findings revealed tissue damage at the interface between calcification and surrounding tissue.

This study investigated stresses and strains at the interface between calcification and fibrous tissue, how these stresses and strains are influenced by local anisotropy of the fibrous tissue and how geometric features of the calcification are related to these metrics. A morphometric study was conducted first, to investigate and categorize different patterns of fiber alignment around the calcifications, and to measure the calcification geometric features including its location in the plaque, its shape and its size. Biomechanical models including the local anisotropic material properties were constructed next, based on the observations and measurements made in the morphometric analysis. Stress and strain metrics were investigated at the calcification boundary, and subsequently related to fiber patterns and calcification geometric features.

Hundred forty five calcifications were segmented and measured in the morphometric analysis, and surrounding fiber alignments were studied. The analysis revealed that four main fiber patterns in the fibrous tissue surrounding calcifications exist: the Attached pattern, Pushed Aside pattern, Encircling pattern and Random pattern. Collagen fibers are attached to the calcification in the Attached pattern, are pushed aside by the calcification in the second pattern, encircle the calcification in the third pattern, and show a disorganized alignment in the Random pattern. The Attached pattern was the most prevalent fiber pattern, and its corresponding calcifications had larger aspect ratios and were on average larger than the other three fiber patterns. Large peak stresses and strains at the calcification boundary were identified in the biomechanical models for the Attached pattern and Pushed Aside pattern, while these metrics showed generally lower peak values for the Encircling pattern and Random pattern. Peak values for all stress and strain metrics were attained at the tip of the calcifications. Multivariate analysis showed that stresses and strains are related to the calcification geometric features; calcification interface stress and strain increased if the calcification was closer to the lumen, had a larger length/width ratio and was larger in size.

Histopathological examination of plaques evidenced damage at the interface between calcification and fibrous tissue, potentially caused by an adverse mechanical state at this boundary. Most studies focused on stresses at the lumen or in the cap however, and this study for the first time specifically investigated stresses and strains at the calcification boundary while simultaneously introducing local fibrous tissue anisotropy in the computational models. Results show that peak stresses and strains can develop at this boundary, which will remain undiscovered if isotropic materials are used. This study was also the first to extensively analyze calcification geometric features and surrounding fiber alignment in relation to these interface stresses and strains. Peak values were found to be dependent on these features and fiber alignment patterns, indicating a relation between these characteristics and mechanical stability of the plaque. The findings of this study further increase the clinical relevance of finite element modeling in rupture risk prediction by showing previously undiscovered peak stress and strain values for interfaces and geometric configurations which already were deemed to be destabilizing in clinical and histopathological studies.

In-situ sample holders with double-tilting capabilities are used to insert and position samples inside a transmission electron microscope for dynamic imaging. However, the performance of these sample holders, regarding energy-dispersive X-ray spectroscopy (EDS) analysis, is not on par with their single-tilt counterparts. By analyzing the EDS influences and the tilting mechanism of double-tilt sample holders, the need for a remote-center-of-motion (RCM) mechanism as a tilting mechanism is identified. Because existing RCM mechanism design strategies limit the design flexibility, a novel design strategy is developed. The novel strategy gives more flexibility in terms of the use of space, design for stiffness and it gives variable input/output link rotation ratio functionality. A compliant proof-of-principle mechanism, which is designed using the novel RCM mechanism design strategy, is manufactured to characterize the accuracy, force/displacement behavior and the input/output link rotation ratio. Analytical, numerical and experimental results are compared, and it can be concluded that the compliant RCM mechanism has potential to be used in double-tilt sample holders.

From the earliest days, the phenomenon of levitation has always aroused the curiosity of humankind due to its mysterious and unique nature. Levitation systems are particularly interesting because of their non-contact characteristic which provides the possibility to isolate the levitated object from environmental effects like mechanical friction and heat flow. The levitation phenomenon can be realized through various principles. However, magnetic levitation distinguishes itself from the other levitation methods since it is the only one that can truly provide passive and stable levitation, without the help of a feedback system or energy input. This is specifically possible because of the phenomenon of diamagnetism, where the magnetization of a material opposes the external magnetizing field. In this thesis, rigid body dynamics of diamagnetically levitated objects have been studied. To do this, an experimental setup has been designed and implemented to simultaneously actuate and measure the response of the diamagnetically levitating object. With the help of electrostatic actuation and measurement of static and dynamic responses of the system, the magnetic forces on a levitating object have been characterized and used to build a rigid body model of the levitating object. Consequently, the interaction between the trapped charges on the levitating conductor and electrostatic forces that were used for actuation have been observed and modeled in the linear regime. By the integration of the mechanical and electrical model, the trapped charges on a diamagnetically levitated object were quantified by several methods, using statical and dynamical measurements. These endeavours have led to the discovery of a unique dynamical phenomenon: Diamagnetically Levitating Charge Induced Impact Oscillator. With the help of the models constructed along theway, the mechanical and electrical behavior of the phenomenon have been explained. Finally it was concluded that the oscillator is also a mechanical charge carrier which can transfer relatively equal amount of charges periodically, where the frequency of transportation and amount of charges transferred depends on the mechanical, magnetic and electrical properties of the system.

The growing needs of nano- and pico-satellite missions require several enhancements in micro-propulsion capabilities to enable the satellites to perform an increasing variety of orbital maneuvers. Among them, the possibility to accurately control the thrust would open up new scenarios for nano- and pico-satellites applicability to include, for example, missions such as space debris removal and orbit transfer.

This thesis presents the design and the implementation of a closed-loop control system for thrust magnitude regulation in micro-resistojets. This is achieved by controlling the propellant mass flow in the micro-valve of the feeding system which is designed to make extensive use of off-the-shelf components. The Vaporizing Liquid Micro-resistojet (VLM) is one of the micro-thrusters under development at TU Delft and, for this reason, it is selected for performing the tests. The outcome of this work is meant to give insights into the design and performance level of future technologies for thrust magnitude control, which will be designed and manufactured at TU Delft. In order to develop appropriate controllers, a non-linear state-space model of the micro-valve system is developed analytically. The model includes different domains, such as electro-magnetic, fluid and mechanical, in order to bring together the complex dynamic behavior of the actuator. The performance of the analytical model is compared to a more sophisticated multi-domain analysis performed with finite element method (FEM) and computational fluid dynamics (CFD). Two controllers, namely PID (proportional-integral-derivative) and SMC (sliding mode control), are designed and tested using the models developed.
The ON/OFF micro-valves are controlled with PWM (pulse width modulation) by tuning the operating duty cycle. A hybrid sliding mode control scheme is developed based on the insights gave by the experiments, which enables the thrust magnitude control of the comprehensive system.
Finally, the closed-loop control system is implemented in the preliminary hardware design of the micropropulsion system. The experimental set-up comprises the propellant tank, the micro-valve, the micro-thruster, the feeding channel, pressure and temperature sensors and the processing microcontroller. The tests are focused on the performance of the controller, and the fine tuning of its parameters, and also in the validation of the design approach.

The controlled micro-propulsion system delivers the commanded input with a response time of ~1.5 s and a resolution of 50 mbar in the chamber pressure. As a first implementation of a control system for micro-propulsion at TU Delft, the results are promising and certainly pave the way for future developments on this research field.