This paper tests the effect of multi-frequency vibrations on the power output of piezoelectric
energy harvesters. These tests were conducted to show how the output power scales when an energy harvester is excited not only at its eigenfrequency, but also at an off-resonance frequency and how well theoretical models predict power output under these conditions. A linear cantilever and bistable buckled beam are tested experimentally on an electrodynamic shaker and simulated using existing models to compare the accuracy of these models under such excitations. The excitation signal has one fixed frequency component, which matches the eigenfrequency of the energy harvester; and a second vibration component, which has a frequency and amplitude that are varied. For a linear cantilever, it was shown that an existing closed-parameter model can predict power output for the mechanical and electrical parameters, where the power is a summation of the power generated by each separate frequency. However, even a simple cantilever shows nonlinearity for high excitations; this is something one needs to account for if you use the model to calculate expected power output.
For a nonlinear harvester it was shown that the power output scales linear with the amplitude of vibration when subjected to a single sine. For multi-sine vibrations, the power output is only slightly increased by adding the second frequency, indicating that the beneficial bandwidth of a nonlinear energy harvester is much smaller when absorbing energy from a second frequency.

The analysis presented in this work confirms that optimizing the diameter ratio and wrap angle is crucial for tailoring the auxetic properties of HAYs. A higher diameter ratio enhances the auxetic effect, making the material more responsive to axial strain with sustained lateral expansion. Conversely, a lower wrap angle improves the initial auxetic response but limits the range of strain over which this response is maintained. These insights are critical for designing materials with desired mechanical properties, particularly in applications requiring specific auxetic behavior within a defined range of strain.

Model 3, introduced in this work, generally provides a reasonable approximation of the contact pressure behavior as a function of axial strain, especially at low strains. However, as strain increases, the limitations of Model 3 become apparent due to its simplified assumptions. The discrepancies observed between the theoretical models and simulation results suggest that further refinement or calibration might be needed to improve their accuracy, particularly in predicting the exact magnitude of contact pressure under different loading conditions.

Overall, this work contributes valuable insights into the design of auxetic materials, offering guidelines for optimizing HAYs' performance while minimizing adverse effects like engulfment. Future work should include experimental validation to fully bridge the gap between theory, simulation, and real-world application, ensuring that the theoretical advancements can be reliably applied in practice.

Linear Variable Filters (LVFs) are integral to future space missions aimed at measuring the spectral features of distant galaxies. Given the varying red-shifts (shift of light to longer wavelengths as an object moves away from the observer) of these galaxies, an LVF with a resolving power of approximately 10 can effectively identify, classify, and image large populations of galaxies, facilitating studies of cosmic evolution through hyperspectral imaging (HSI) techniques. HSI captures detailed spectral information across a wide range of wavelengths for each pixel in an image, enabling material identification and analysis. Since the galaxies to be studied are very faint, hyperspectral imagers need to be equipped with highly sensitive detectors, cryogenically cooled conditions, and filters with high transmission efficiency. This thesis investigates LVFs based on thin membranes, focusing on materials like silicon nitride (Si3N4) and silicon carbide (SiC). The primary objective is to model these thin and pre-stressed membranes using COMSOL Multiphysics to simulate the thermal expansion and mechanical behaviour of membranes in cryogenic environments. Experimental validation is conducted using Digital Holography Microscopy (DHM) and Laser Doppler Vibrometry (LDV) to ensure the accuracy and consistency of the simulations. The model enables the simulation of membranes with varying dimensions, improving the accuracy of behavioural predictions thereby eliminating the need for physical prototypes for analytical purposes, significantly reducing cost and time. Overall, this research bridges the gap between theoretical models and practical applications of LVFs in space. Enhancing the understanding of material behaviour under extreme conditions advances the development of reliable LVFs for spaceborne optical instruments, offering valuable insights into their durability and performance.

For the design of new manufacturing methods for mechanical metamaterials in compact motion systems, a new bonding technique has been developed. The manufacturing technique requires thermoformed PEEK films to be bonded together. Literature review has shown that laser welding, and specifically laser transmission welding, is a valuable method for this manufacturing technique, particularly for bonding materials that are tens of microns thick, such as thermoformed and PEEK films. This research demonstrates how to define a viable process and how to optimize laser parameters to achieve maximum joint strength and identifies factors that can diminish the quality of the bond, thereby affecting optimal speed.

Further investigation of the PEEK and absorptive coating spectral curves has revealed that absorption coating is effective in increasing the absorbance used in this research. Welding with an infrared laser around one µm wavelength can rapidly produce strong welds, where the tensile strength of the welds exceeds that of the material. A fluence of around 20 to 30 mJ/mm^2 results in optimal weld peel strengths.

The optimal parameters for 125 µm lap welding include a speed between 10 and 15 millimeters per second and a defocussing distance between 4 and 7 millimeters. The thickness of the welded films range from 25 to 125 microns. It has also been observed that thicknesses of 25 and 50 micrometers can produce welds with 125 thick thermoformed PEEK films, allowing for 2.5D film welding capabilities.

The manufacturing of sensors often requires the precise deposition of small volumes of liquid. In order to do this, expensive industrial equipment is often used, giving this form of manufacturing a high financial barrier to entry. As standard desktop inkjet printers operate by precisely depositing small volumes of paper onto a substrate, typically paper, the goal of the project was to modify a desktop inkjet printer, the Epson EcoTank ET-8500, to allow it to be used to deposit small droplets of fluid onto a CMOS sensor chip.

This report covers the design process of the hardware modifications that were necessary in order to allow the Epson EcoTank ET-8500 to print onto CMOS sensor chips packaged in a QFP- 44 package. These modifications include a custom chip tray to safely house the chips as they go into the printer, as well as an external fluid system to allow the user to easily use ink other than the stock ink provided by Epson or to put a cleaning fluid into the system in order to clear out any residue deposited by the inks used.

The results obtained indicated high levels of precision, and the system’s accuracy was sufficient for the sensor chips used. The external fluid system was also tested and successfully allowed the printer to work with fluids not placed into the built-in tanks.

Green hydrogen produced by water electrolysis is one of the most promising technologies to realize the most effective way of utilizing intermittent renewable energy globally. Among the various electrolysis technologies, the emerging Anion-Exchange Membrane Water Electrolysis (AEMWE) shows promising potential for producing green hydrogen at a competitive price.

The low ion conductivity of the Anion Exchange Membrane (AEM) is found to be one of the major limitations of AEMWE. In this thesis, the AEM is aligned while casting using an alternating current electric field to improve the ion conductivity of AEMs. The stability of the electrically aligned membrane is tested using various characterisation techniques. The electrically aligned membranes showed a 300% increase in ion conductivity, with a slight decrease in mechanical stability.

Inkjet printing is a technology that has been widely studied and implemented. The liquids that are used for inkjet printing can vary. There is the traditional ink which can be found in almost every household printer. But it is also possible to use inkjet printing to deposit drugs, proteins and nanoparticles on substrates. Inkjet printing has the ability to precisely deposit picoliters of liquid onto the substrate. Thus, reducing cost and waste when the material being used is expensive and/or of limited quantity. This project works with a LP50 PIXDRO inkjet printer. Another interest that gained traction in the scientific community are the stimuli-responsive microgels. These microgels are able to change their dimensions depending on the external stimuli and if this stimuli is removed from the microgel, it changes back to its original shape, thus it is a reversible process. This project uses a suspension of the stimuli-responsive microgel; poly(N-isopropylacrylamide)-coacrylic acid (pNIPAm). This microgel is responsive to temperature and pH. To deposit the pNIPAm suspension on the substrate, inkjet technology will be used. The printability of the pNIPAm will be determined by characterizing the physical and rheological properties. Such as the density, surface tension, viscosity and particle size of the pNIPAm beads. These properties will be compared to the ideal liquid requirements given by the print cartridge that will be used, a Fuijifilm Dimatix. To influence the surface tension three surfactants will be tested. These surfactants are Triton X-114 (TRT), Sodium dodecyl sulphate (SDS) and Hexadecyltrimethylammonium bromide (CTAB). Based on the results the and comparison to the requirements the surfactant Triton X-114 is chosen because it lowers the surface tension the most. While it has minimal to no affect on the pNIPAm particles. The next phase of the project is testing the printability of the pNIPAm. This is done by adjusting the waveform on the LP50 PIXDRO inkjet printer. As a result it is indeed possible to deposit pNIPAm on a substrate with an inkjet printer. After this step a SEM is used to investigate if the printed pNIPAm particles will form a monolithic layer. This monolithic layer is important when it comes to having a functional etalon. The pNIPAm particles form indeed a monolithic layer on the substrate. The last step is to see if there is a peak shift in the wavelength when the temperature is increased. The microgel based etalons that used an inkjet printer to deposit the micrgol show a peak shift. Therefore, it can be concluded that it is possible to use an inkjet printer to deposit pNIPAm on a substrate and that the pNIPAm particles behave according to literature. All the results of this project show that using an inkjet printer is a viable alternative for fabricating microgel based etalons.

Micromechanical resonators, which have become feasible due to advanced manufacturing techniques, have shown several interesting phenomena including mode coupling in a range of applications that span metrology and sensing. Conventional fabrication methods of these resonators have been used throughout the field. However, fabrication of micromechanical resonators by femtosecond laser ablation which could accelerate prototyping, access to three dimensional resonators and reduce clean room use, has received little attention.

In this study, a protocol for fabricating and measuring laser cut micromechanical resonators using computational analysis and experimental techniques has been developed and validated through comparison with previous works by characterising doubly clamped beam resonators. The fabricated prototype is demonstrated to exhibit autoparametric resonance and coupling showcasing the potential of the new approach in engineering and fast prototyping of coupled micromechanical resonators.

Nanomechanical tests to investigate Diamond-Like Carbon (DLC) coating abrasive wear behavior were carried out under different load and strain rate conditions. Nanomechanical tests performed include nanoindentation, single and multi-asperity scratching tests. Characterization methods used are confocal optical microscopy, SEM/EDS, and (high-resolution) AFM. The counterpart material used is diamond.
Results show that DLC abrasive wear behavior is predominantly plowing. Increasing normal load results in wear debris at the edge and inside the wear scar. Failure occurs between DLC and substrate (in this case SiC), upon further increasing the normal load which is in agreement with the literature. In addition, it is found that strain rate influences DLC wear behavior with increasing normal load. This implies that DLC/SiC interfacial adhesion strength presents strain rate dependency rather than DLC itself. This is supported by nanoindentation measurements, where no strain rate dependency was observed. Therefore, for a DLC coating operating under high loading (≥100mN per asperity) in an engineering application, single-asperity testing is not representative of the engineering application. This is caused by the limitations of single-asperity test setup reaching strain rates close to that of the engineering application.
Further, it is reported that in multi-asperity scratching tests increasing the normal load affected the scratch density rather than scratch depth and width. This implies that there is a range of macroscopic normal loads that corresponds to similar single-asperity wear behavior. Scratching tests performed at the edge of DLC/SiC wafers showed that edge wear depends on the rate of change of asperity interference (ω ̇) during collision with the edge. Moreover, an analytical model was developed which predicts that minimization of the impact force (and thus wear) is accomplished when ω ̈ takes minimum value. Based on this criterion minimized edge wear takes place when the asperities are relatively sharp (~1μm) and their initial interference does not exceed 30% of the coating thickness.

Reluctance actuators boast a high motor constant in small air-gap applications when compared to Lorentz actuators. Inherent non-linearities in the F-I relation limit force predictability. Replacing conventional current control with flux control can greatly improve force predictability. Traditionally, hall sensors or hysteresis modelling are employed for accurate flux estimation. This thesis proposes a calibration strategy and control architecture for hybrid flux estimation. The novel control architecture is implemented on a test set-up at MI-Partners. The flux estimator consists of a high pass filtered sense coil and a low pass filtered current probe for integration drift correction. Through comparison of force estimation errors due to magnetic hysteresis, (analog) integration drift and integration errors the optimal crossover frequency was calculated to be 13 mHz. The hybrid control architecture is capable of force prediction accuracy on par with hall control. Simulated positioning accuracy even shows an improvement of 13%, simulations show an improvement in maximum error from 423  micrometer to 369 micrometer. A positioning accuracy improvement of up to 332% over a similar current controlled system has been demonstrated.

In mechanical systems, energy efficiency is often reduced by unwanted forces like friction and backlash, which significantly impact performance and, over time, lead to increased wear and maintenance costs. Implementing compliant joints can address these issues, simplifying assembly and improving performance. However, compliant mechanisms introduce higher internal loads due to elastic deformation in the flexures, limiting the range of motion and affecting overall efficiency. One way to solve this is using the principle of static balancing, which ensures that a point of interest remains in equilibrium, meaning that no added forces or moments are needed to keep it at rest at certain positions. This can be done by compensating the internal potential energy, which has been implemented in literature for 1 Degree of Freedom configurations. The goal of this paper was to expand the known method into designing a multi-degree of freedom without the use of external springs. The method was based on applying a preload to the compliant joints in the mechanism and optimize in such a way to create a constant potential energy curve. The model was validated using finite element analysis, prototyping and physical testing. It can be concluded that for the first time, a two degree of freedom statically balanced mechanism has been designed. It has a peak force reduction of $95\%$ and a moment reduction of $80\%$, while having a range of motion worth $50\%$ of the size of the mechanism. The mechanism can be used in vibration isolators or as fundamental inspiration for new applications where preloading could lead to lower exerted loads and thus improve efficiency.

This thesis report contains two papers. The first paper is a literature study on mechanisms, smart actuated materials and controllable joints. In this paper, several smart materials are identified and it is discussed how they can be embedded in different mechanisms. From this paper, it is concluded that fast-response smart material twisting actuators do currently not exist. The second paper studies the design and development of such an actuator. The study presents a design and manufacturing methodology of a planer actuator that generates out-of-plane rotation. It first investigates different out-of-plane deformation modes and how they can be used to achieve the desired motion. Based on an analytical model on the shape morphing of piezoelectric macro fibre composites, a methodology is developed to generate out-of-plane twisting deformation. This concept is used to design a carbon black electrode pattern, which can be spray-deposited on a kapton substrate. This electrode is subsequently used to selectively actuate parts of a P(VDF-TrFE- CTFE) polymer layer. The selective stimulation of the layer results in the desired twisting deformation. This study demonstrates how flat designs can be laminated in a planar additive manufacturing process to induce complex 3D motion. The spray-deposition process was capable of manufacturing bimorph actuators with a 1.6mm resolution. The resulting actuators have a length of 41mm and a width of 10 to 20mm and a thickness of 120 to 139micron. The experiments are used to characterize the effect of the design parameters such as actuator width and thickness on the magnitude of the deformation. As theorized in the analytical model, the thinner more slender samples show the largest rotation which is measured to rotate up to 3.38 degrees. From the experiments it is also found that thinner samples show dielectric breakdown at much lower voltages, around 100V, compared to thicker samples from the same design that performed up to 480V. The study also investigates the quality of the deformation of the actuators, i.e. pure twisting or a combination of twisting and bending deformation. It is verified that uneven layers or asymmetric actuators show significant unimorph bending behaviour, with displacements up to 1.5mm while rotating 3.38 degrees. To the author's best knowledge, this study presents the first working prototypes of fast-response smart material twisting actuators.

Cerebral oxygen saturation is an important indicator that reflects the oxygen metabolism of the brain tissues in such patients. The utilization of near-infrared spectroscopy (NIRS) enables the identification of the oxygen saturation levels in nearby tissues by analyzing the distinct oxygenation states of hemoglobin-oxyhemoglobin (HbO2) and the distinctive molecular spectrum of deoxygenated hemoglobin (Hb). It is helpful to realize the objective of noninvasive continuous detection on cerebral oxygen saturation because near-infrared radiation can directly penetrate the skull to obtain the characteristics of the average oxygen saturation of the brain tissues. This also allows a noninvasive way to monitor blood flow in the brain. A frequency comb is a pulsed laser in the time domain and a sequence of discrete, uniformly spaced frequency lines in the frequency domain. Applying the frequency comb to NIRS has the potential to develop a high-speed and fs-level time-of-flight resolution blood flow measurement system. The objective of this thesis is to utilize a chip-based optical frequency comb as an illuminating source in order to conduct time-of-flight measurements of a single target, employing a Michelson interference experiment. The establishment of the time of flight in the single-layer case and the investigation of the non-ambiguity range form the fundamental basis for future experiments multi-layer.

Mode coupling has extensive use in the MEMS field, including frequency division, vibration direction conversion, and energy transfer. In practice, these applications can be used to improve the performance of various devices such as sensors and energy harvesters. Nonlinear spring also has a wide application in MEMS field. Various nonlinear spring mechanisms, such as fixed-angle bows, bistable rotational mechanisms, H-shaped springs, and topology-optimized planar springs, have been proposed and utilized. Nevertheless, there is a lack of non-electric design elements specifically designed for mode coupling. This thesis proposes a simple system demonstrating the feasibility of using a nonlinear spring to achieve mode coupling. The system incorporates a spring-mass system with two mass blocks, two linear stages, and a unique nonlinear spring compliant mechanism. The integrated components can be fabricated using 3D printing resin or high-precision femtosecond laser-cutting of silicon wafers. Additionally, a new crank-slider structure and a spline-shaped nonlinear spring are developed and studied for this system. Each has advantages and disadvantages, and is suitable for systems of different sizes and materials respectively. Their load-displacement relationship roughly satisfies the cubic relationship, but still has a linear term. The proposed system holds potential for enhancing the performance of sensors, energy harvesters, and other MEMS devices.

inPhocal, a startup company specialized in laser marking, developed a novel optical module to make the depth of focus more than 50mm, and wants to replace ink marking by this laser marking system in the production line when marking information on products. Distortion will always happen when marking 2D patterns onto 3D objects with laser, so deforming the 2D patterns beforehand to make marked pattern keep its shape is necessary. This process is called shape correction. Nowadays, the way to do this shape correction is very complicated and time- consuming. This thesis is focused on providing a new method that can do shape correction easily and fast. In this research, Non-Uniform Rational B-Spline (NURBS) is used in reconstructing the 3D surfaces and the shape correction will be based on these NURBS surfaces. With this NURBS-based shape correction, the pattern can be mapped on to 3D object fast without distortion.

Flying drones have been a well-established field of engineering for many years now. With the wave of bio-inspired design came the idea of flapping wing micro air vehicles (FWMAVs). These drones use flapping wings instead of fixed or rotary wings to generate their lift, giving them the potential for agile movement and application in confined spaces. The Atalanta project is one of the groups trying to create a working and efficient FWMAV. While a lot of progress has been made in optimizing the flying motion, the vehicle so far does not have a control mechanism yet. This master thesis seeks to compare methods to achieve this control and propose a final design for a hinge that will be verified experimentally.
A selection of materials and methods for inducing structural changes is tested using analytical models. After picking the most viable options a numerical model seeks to find which of the remaining materials or methods has the highest effectiveness given a set of volume constraints. The most effective design is adapted into a proposed final design for the Atalanta project. The theoretical finalized design fulfills the constraints and functions using a voltage as low as 15 V. To verify the physical principle behind the design experimentally, a few changes are made to the design to allow the construction of a simplistic measurement setup. After the experimental validation it is concluded that the design in its current form is not effective enough to achieve control in the Atalanta FWMAV, and some suggestions are offered to improve the design in future research.

Achieving appropriate soft tissue tension around the hip joint is an important factor for achieving hip stability after Total Hip Arthroplasty (THA). Hip instability leads to dislocations, pain, and is a common reason for early revision surgery. The current soft tissue tension assessments available during surgery rely on experience, and dislocations occur twice as often after THAs performed by inexperienced surgeons compared to more experienced surgeons. This paper presents a new mechanism which measures and displays hip force in Three Degrees Of Freedom (3-DOF) during THA. A prototype measured axial and normal force components up to 75 N with a sampling frequency of 14.6 Hz, an accuracy up to 11 N, and a Root Mean Square Error (RMSE) of 4.0 N (axial) and 3.0 N (normal). Additionally, it measured the normal force direction with an accuracy up to 7.1∙10^(-2) π rad and RMSE of 7.1∙10^(-2) π rad. Data needs to be collected to build a predictive model which estimates the required hip force range and distribution to achieve a stable joint. When combined with such a predictive model, the proposed design is a promising assistive surgical tool.

When we manipulate objects in our day-to-day life, we perceive information on the object via force feedback that we sense with our sensorimotor system. However, in virtual reality, we lack these forces, which makes it more challenging to interact with the digital world. Wearables, such as hand exoskeletons, can provide force feedback in VR. Nonetheless, as the devices’ actuation or brake system is often bulky or heavy, users typically do not enjoy wearing them. In this study, we investigate the potential of a new friction-based mechanism that can address the existing issues. Our design adopts ultrasonic vibrations to generate a squeeze film, which is a well-studied phenomenon to decrease friction significantly. In literature, the phenomenon has only been investigated with vibrations from one side, with the goal of friction reduction. However, we show that by adding a vibrating surface opposite to the original one, we can extend the possibilities of squeeze films, enabling us to both decrease and increase friction. Since ultrasonic transducers can be miniaturized, our mechanism brings us closer to solving the size and weight issues of existing devices.