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.

When a free-standing membrane is actuated with photothermal method, the heat flux requires a certain time to diffuse through this membrane. This duration of time, called thermal time constant, is important for its application in sensors, nano-electromechanical systems, filters, etc. This report is devoted to exploring what plays a major role in the variation of experimentally measured thermal time constants, and to investigating the relationship between dumbbell dimensions (namely, two drum radius R1 for drum 1 and R2 for drum 2, half bridge width y0, bridge length x0) and thermal time constants.

First, dumbbell resonators of various dimensions were fabricated using exfoliated molybdenum disulfide flakes. Optomechanical experiments were conducted on these devices, involving two collocated (actuation and measurement located in the same drum) and two non-collocated (actuated at one drum and measured at the other) measurements for each device. Accordingly, four thermal time constants were extracted for each resonator through curve fitting. To understand temperature distribution and experimental variation, a COMSOL model and an analytical model were established, solving the heat equation with a harmonic laser actuation.

As a result, four thermal time constants for 16 devices were extracted. These experimental data were verified with a synergy of the two models. The primary contributors for large experimental data variation were the 2D material irregularities and laser locations. For collocated τ, it was almost unaffected by dumbbell dimensions, except for R1 which gave a parabolic curve. For non-collocated τ, it increased monotonously with x0, but a minimum was always observed when sweeping the other three parameters.

Such minimum occurred when x0 is around 25% of the drum radius. This minimum was attributed to a balance between the efficiency of heat transport across the bridge and the acceptable duration required to heat the bridge itself. Meanwhile, the COMSOL model and the analytical model disagreed on the relationship between non-collocated τ and y0, R1, R2. Moreover, the analytical model’s deviation from the COMSOL model increased with larger bridge width or thermal conductivity. This stemmed from errors in the assumed boundary conditions: the existence of the bridge altered the temperature distribution at the boundaries of drum 1, and in the analytical model the boundaries of the dumbbell are fixed while in the COMSOL model they are controlled by the substrate.

systems. Miniaturization creates challenges in handling delicate, small components, rendering traditional methods inadequate, necessitating an alternative. Acoustic levitation, which uses ultrasound waves to suspend objects without physical contact, offers a promising solution for containerless transportation. This technology can accommodate various materials regardless of their electromagnetic or optical properties and eliminates particle generation due to friction. Applications span across chemistry, biology, and high-tech industries, enabling manipulation and assembly of small components. However, acoustic levitation is highly sensitive to environmental factors such as temperature and air currents, which can compromise stability. Most studies have primarily focused on understanding the dynamics of acoustic levitation and developing models to describe the underlying physical phenomena. This study shifts towards actively controlling them by adding artificial damping. To achieve this, this thesis introduces the use of event cameras, which capture high-speed movements without redundant frame data, making them highly efficient. The goal is to create a control feedback loop to correct for disturbances and improve the step response of acoustically levitated objects. The methodology involved integrating an event camera into the acoustic levitation setup and implementing a tracking algorithm to track the position of a levitated object. System identification was performed, revealing higher-order harmonics and allowing the development of a second-order model of the levitated object. This model was used to design a feedback controller integrated with the event camera. Experimental results demonstrated a substantial improvement in system performance. The bandwidth of the system improved to 40.8 Hz, the settling time decreased from 10 seconds to 0.8 seconds, an improvement by a factor of 12.5. Additionally, the steady-state error was significantly reduced, and the introduction of artificial damping successfully eliminated the first resonance peak, though a second higher-order resonance peak remains. This work highlights the potential of using event cameras in control loops for acoustic levitation, representing a significant step towards more precise control of levitated objects.

This study explores the design and implementation of an electrowetting-on-dielectric (EWOD) system for precise die positioning in a chip assembly environment, utilizing a millimeter-scale ”chip-on-droplet” approach. Two methodologies were investigated: coarse positioning using digital signals, a method well-documented in prior research, and fine positioning using analog signals, which, to the best of our knowledge, had not been applied to droplet positioning at the time of writing. The primary advantage of the fine positioning approach lies in its independence from feature size, allowing for significantly smaller step sizes. Experimental results demonstrated that the analog system achieved step sizes as small as 3.5 μm in a ”droplet only” setup, outperforming the ”traditional” coarse positioning system. Performance limitations were found to arise primarily from the tracking setup rather than the EWOD system itself.
The study also evaluated various surface layers, confirming prior findings that a smooth, thin, and homogeneous surface layer is critical for achieving consistent and precise movement. Attempts to en- hance droplet guidance through modified surface structures were unsuccessful due to pinning forces exceeding the generated EWOD forces. These findings highlight the potential of analog signal-driven EWOD systems for fine positioning applications, with important implications for chip assembly tech- nologies.

Electric and hybrid vehicles are a common sight on the roads these days. The electric machine is known to be quiet, but sometimes high-frequency sounds are observed when driving. Over the years many different solutions have been developed to make the electric machine quieter, but almost no research looks into the possibility to generate sounds. This thesis looks into the possibility to produce nice sounds and reduce annoying sounds with electric machines. This is done by introducing harmonics into the current and creating additional excitations of the structure. To gain a complete understanding of this topic the electromagnetic domain and the structural domain have been analysed. A mathematical description of the forces has been created to be able to make predictions about the forces created by an injected current harmonic. Using the electromagnetic model the exact influence of current harmonics on the forces has been verified. The sound power level produced by the forces acting on the structure is calculated using the structural model. By properly selecting the current properties it is possible to create new temporal orders that produce sounds. For the analysed electric machine the sound power level of the desired sound is on average approximately 20dB lower than the sound power level of the fundamental current. Furthermore the sound power level is dominated by the excitation of the breathing modes. Using current injection existing sounds can be reduced. Using brute force optimisation the average radial forces were reduced. This reduces the sound power level during most of the run-up and reduces the influence of the breathing mode by up to 11dB. At some points during the run-up more sound is produced, because the tangential forces are increased, while the radial forces are decreased. In the end it is shown that the influence of the introduced current harmonics on the acoustics can be analysed using mathematics and the simulation results. New sounds can be produced, but the sound power level is limited by structural design of the electric machine.

Nanomechanical resonators made of two-dimensional (2D) materials are the subject of intensive research due to their remarkable properties, allowing them to operate at high frequencies with high sensitivity. However, dissipation losses and manufacturing issues have prevented them from reaching their full potential. This thesis aims to overcome these challenges by dry-transferring 2D materials onto a MEMS and clamping them using electron beam-induced deposition. By in-plane straining the membranes using MEMS, the tensile energy is increased, thereby diluting intrinsic losses. This approach increased the Q-factor of 2D material resonators by 91% and allowed measuring forces down to sub-piconewtons, outperforming commercially available silicon-based force sensors.

Photonics biosensors convert biomolecular interactions into quantifiable optical signals for biomedical analysis, which enable continuous monitoring of health indicators. Among them the microring resonator has a good sensing performance and a very broad application prospect. This thesis studies sensing with microfluidic integrated microring resonator photonic microchips.
This thesis adopts finite element method to simulate the optical behavior of waveguides and reactions in the microfluidic channel. The microfluidic channel was designed and prepared and then integrated to the photonic chip. The optical performance parameters of the micro ring resonator were tested by using a high-precision optical test system. The sensing performance of waveguide microring was studied using different aqueous solution as the detection object. The feasibility and effectiveness of the optical waveguide chip sensing have been preliminary verified.

Surface acoustic wave (SAW) is widely used in biological research and sensor applications, acomprehensive understanding of SAW propagation and visualization on suspended 2D membranes is crucial for the manipulation of nanoparticles in biological research and sensitivity improvement of SAW sensors based on 2D material. The initial step of this project involved exciting a standing SAW field on the SAW device and attempting to use Digital Holography Microscopy (DHM) for imaging the standing SAW field on the substrate. This attempt was very challenging and unfortunately was not successful. We used an Atomic Force Microscope (AFM) as an alternative solution for SAW field imaging. Initially, AFM was used to image the SAW field on the SAW device substrate, and the impacts of input frequency and power on the amplitude of the SAW field were investigated. Subsequently, microcavities were fabricated on the SAW device to record images of the SAW field within the microcavities and their surrounding areas, aiming to investigate the impact of microcavities on the SAW field. Finally, the prepared graphene membrane was transferred to the microcavities, the SAW propagation was recorded on the suspended membrane and the influence of the suspended membrane on SAW propagation was analyzed.

Silicon photonics have received more attention in recent years due to further development in CMOS manufacturing methods. The development allows silicon photonics to be smaller than ever before. This leads to smaller silicon photonic devices that can transceive light, which is typically done at a wavelength of 1550nm for silicon photonics. A silicon photonic device that benefits from this wavelength is the silicon waveguide, which can transceive light by being coupled to other waveguides. When the second guide is later coupled back with the main waveguide, a resonance can form between the guides. This can turn the silicon waveguide in to a sensor that relies on interference from the recoupled signal. The design used for this study has the waveguides in a relatively deep trench, which means that a membrane can be suspended above the waveguides. In theory the membrane should reflect some of the light that escapes from the waveguide back. In this work membranes made from graphene and molybdenum disulfide are suspended over a silicon waveguide in hopes to detect the motion of the membrane. A proof of concept by experimenting with membranes integrated on silicon photonics can give way for a new type of sensor, which is both microscopic and has a high signal-to-noise ratio. The experiments are conducted by propagating light through the waveguide, the light should then interact with the suspended membrane on top. The first indication that the concept was possible was when a transmission graph that swept the light’s wavelength around 1550nm changed after introducing a suspended membrane over the waveguide. The change showed that waveguides react to membranes over them without eliminating the transmission altogether. This is a great step when it comes to a proof for the concept. However, it is still needed to take a frequency measurement before the concept has been fully proofed.

With the increasing demand for extended service life and increased precision and accuracy of precision mechanics across various industries, machine tool manufacturers face the challenge of increasing the performance of their machines. To achieve this goal, the performance of the machines must be evaluated, points of improvement must be identified and subsequently be acted on.

This thesis is focused on the evaluation of the dynamic performance of a two-axis CNC lathe, subject to vibration modes excited by movement of the machine axes. To this end, two experiment setups are designed to measure displacement at the cutting tool in either axial or lateral directions and compare these displacements against the positions and controller setpoints of the corresponding machine axes. Additionally, a finite element model is created and expanded such that it emulates the machine encoders and additional cutting tool sensors, as well as the third order motion profile that is used to excite the system. Methods for automatically processing the data from these experiments and simulations are developed in parallel, allowing for large sets of data to be processed with little effort.

These experiments show that with a maximum amplitude of approximately 0.3 μm the vibrations that occur at the tool, relative to the axis encoder, are most significant in axial direction. A qualitative comparison with the finite element model indicates a mechanical issue relating to the Z axis drive mechanism, causing additional vibrations in the system. Finally, the experiment setups, corresponding data processing methods and finite element models are reflected on and incorporated into a framework for experimental machine performance evaluation. By implementing this framework, machine tool manufacturers can further evaluate and improve the dynamic performance of their machines.

From the research in the field of mechanobiology, it is evident that cells exert different force magnitudes while growing based on the biomaterial these are in contact with. The magnitude of the exerted force determines certain behaviors and mechansims of the cells, such as differentiation. For this reason, it is proposed to develop a distributed force sensor using a photonic integrated circuit with a PDMS top layer to measure the exerted forces, which can be used to study the behavior of the cells. Unlike conventional measurement techniques, this method allows cell exerted distributed forces at µN levels to be detected and monitored over a continuous time-span of multiple days and weeks. The photonic integrated circuit design consists of a sensing array of silicon photonic ring resonators for force sensing. On each sensor row, reference ring resonators are applied as well to cancel out the spectral noise caused by temperature drifts and laser wavelength repeatabilities. The reference ring resonators are shielded against cell exerted forces with a commercial hybrid-polymer, which has a Young's modulus of around 1 GPa. Using the reference ring resonators resulted in a theoretical measurement resolution of potentially as small as approximately 0.012 pm. Finally, the force limit-of-detection of the designed distributed force sensor remains below 1 µN when the force exertion area does not exceed 100 µm2 and assuming a sensitivity of 65.41 nm/RIU for one of the multiplexed ring resonators.

Acoustic levitation is an novel method that could lend itself very useful to fast and precise transportation of small objects. To verify the acoustic field and the modelling assumptions, the acoustic field must be visualised and quantified. Different methods to visualise a pressure gradient are investigated and rated against design requirements. These requirements are: 1. difficulty, as the setup should be buildable within the period of a MSc. thesis. 2. Time per measurement and 3. measurement sensitivity. It is decided that using a double coincidence spherical mirror schlieren setup is most suitable measurement method. To capture the high speed sphenomena of ultrasound acoustic waves in air, the schlieren light source is pulsed and matched to the frequency of the acoustics to ’freeze’ the acoustic wave in the air. Parameters that influence the schlieren image are identified and studied. These parameters are duty cycle, cut-off, ISO, light source phase delay and light source frequency. A horizontal cut-off is determined as the best, while it is determined that the other parameters can be adjusted dependent on the acoustic field. The acoustic field generated by double phased array is observed. Trap locations and types can be identified using the schlieren system. Quantification of the schlieren images has been attempted but without satisfactory results, mainly due to an interesting observation regarding a correlation between the camera focus distance and the pressure gradient. The schlieren system is a useful research tool and successful at visualising
the pressure gradient under the assumption that it is constant over the optical axis. Further research is needed to for quantification and to assess the impact of the observation.

Two-dimensional (membrane) materials have been receiving much scientific attention due to their unique material properties that can be used to study the smallest physical phenomena. One such material is graphene, perceived as the holy grail in material physics, due to its unique material properties. Its aspect ratio diminishes the bending rigidity and allows wrinkles, ripples and other morphological imperfections to dominate the mechanical behaviour. Applying tension is a necessity to control these geometrical imperfections and simultaneously opens up pathways to study physical phenomena such as magnetism, superconductivity, optics and much more. Typically, this tension is applied using electrostatic forces, which alters amongst others, the electric properties of the material. Mechanically applied tension offers a solution to this problem but comes at the cost of difficult manufacturability. In this work, a new method to incorporate 2D materials with N/MEMS is presented. The dynamics of mechanically tensioned graphene are probed in linear and nonlinear regimes. The former regime finds the exact opposite of what is observed in electrostatically tensioned membranes. The latter shows exotic nonlinear effects that can be tuned by applying tension. Furthermore, it is identified that the dynamics of the MEMS device are coupled to that of the resonating membrane despite their mass and stiffness being roughly five orders of magnitude apart. The bottleneck of this project is the adhesion force between the two is insufficiently strong to apply significant strain allowing slippage to occur.

Mechanical forces are integral to the functionality and behavior of biological systems, from the cellular to the molecular level. Acoustic force spectroscopy (AFS), an emerging field, seeks to explore these intricate dynamics. Traditional methods in AFS, particularly those using bulk acoustic wave (BAW) devices, still lack sample visibility and have a low throughput. These limitations hinder the amount and type of data that can be gathered in the study of cellular and molecular mechanics. This research project addresses the challenge of enhancing visibility and throughput in AFS by developing a novel BAW device. Here we show the fabrication and implementation of a glass transversal resonator by femtosecond laser ablation and a simple glass-glass bonding technique using polyethylene film and cyanoacrylate glue, which enables two-dimensional particle trapping. Compared to existing BAW setups in AFS, our approach offers improved sample visibility and is capable of positioning particles at arbitrary locations between half- and full-wave mode equilibria by rapid mode-switching. It shows that the position can be predicted using a straightforward method to determine the stiffness of each mode. This advancement of acoustic force spectroscopy could pave the way for new approaches in biomedical research. For example, the ability to alter the force field in a predictable manner allows to form both force- and distance-clamps. More functional BAW devices could thereby not only enhance our understanding of cellular processes but also find broader application in fields like tissue engineering and medical diagnostics.

Research has shown concepts of phononic integrated circuits (PnICs) consisting of multiple acoustic waveguides and beam splitters. Traveling acoustic waves experience energy loss when moving. Minimizing these losses is critical for large and complex PnICs. By fabricating on-chip PnICs, it is possible to operate under vacuum and at low temperatures resulting in lower acoustic losses.
Studies have shown on-chip data transport using straight acoustic waveguides fabricated inside suspended membrane phononic crystals. The use of high stress Silicon Nitride (SiN) has enabled
the manufacturing of high aspect ratio suspended structures. This is achieved by stress keeping the membrane under tension resulting in a flat surface.
Current acoustic beam splitter designs feature liquid and air for the wave supporting material. Making them not suitable for on-chip devices. Therefore, on-chip PnICs require a new type of splitter
design.

In this study, finite element methods are used to investigate if suspended SiN membranes offer a solution for on-chip acoustic beam splitting. The wave confinement of square and hexagonal lattice splitters are also compared to find the best performing design. Phononic bandstructures are constructed by performing eigenfrequency studies on various 2D phononic crystal unit cells. These bandstructures reach full GHz bandgaps with relative bandgap sizes of 57.3%.
Symmetric beam splitters are then made by introducing line defects into the crystal structures. Multiple wave excitation locations, frequencies and waveguide widths are investigated to establish the highest wave confining splitter design. The final design consists of a y-shaped splitter inside a suspended SiN hexagonal lattice phononic crystal and achieves a wave confinement of 85.03% at an excitation frequency of 3.25GHz.
The results show that suspended SiN membranes featuring hexagonal lattice phononic crystals offer a promising solution for on-chip beam splitting.

Acoustic Force Spectroscopy (AFS) is a versatile tool that uses sound waves to manipulate tiny particles such as cells, bacteria, and even zebrafish embryos in microfluidic systems. This kind of acoustic tweezer is gaining increasing attention due to its high throughput capability and non-invasiveness. In addition, this device allows for parallel manipulation of bio-molecules. Therefore, it can provide statistically significant data about the DNA replication process, which is widely considered a stochastic process. Understanding the dynamics of the DNA replication process plays a vital role in developing medicine to cure diseases that are still incurable today. Most single-molecule techniques, such as optical tweezers, magnetic tweezers, and atomic force microscopy, can only manipulate a limited number of particles simultaneously. Therefore, obtaining statistically significant data with these methods is laborious, time-consuming, and expensive. This report describes the design, fabrication, simulation and characterization of an easy-tobuild and cost-effective acoustic tweezer. The trapping stiffness of this device is derived from finite element modelling and experiments. This property is used to benchmark the acoustic tweezer developed in this project against other microparticle manipulation devices found in the literature. The results show that the acoustic tweezer developed in this project provides sufficient trap stiffness for studying DNA replication.

Over the past few years, sub-surface imaging techniques at the nano-scale have become increasingly important in the semiconductor industry, whereby voids, cracks and other heterogenous features can be detected using disturbances in penetrating waves inside the substrate. A certain modality called photo-acoustic subsurface Atomic Force Microscopy (passAFM) is currently in development at the DMN group in TU Delft. PassAFM uses two fs pulsed lasers to generate and detect acoustic waves inside an AFM cantilever. This technique promises a lateral resolution of subsurface imaging in the order of the AFM tip size. It is required to focus the acoustic waves inside the tip and obtain sufficient acoustic power to detect a signal back from the tip. Therefore, acoustic lensing devices are designed and the improvement in detected signal is studied in this research.

Micro-ring resonators based on silicon-on-insulator (SOI) waveguide are widely used as sensors due to their small size and high sensitivities. After being fabricated on an integrated photonic technology, it can be applied in bio-chemical analyses crucial for human health monitoring, disease diagnoses, etc.
In this project, we develop and construct a robust experimental setup based on the SOI based micro-ring resonator, which combines temperature control and modification of the waveguide cladding via surface treatments and microfluidic integration. The setup gives a controlled environment for characterizing the photonic chip under various chemical treatments or different physical ambient.
After the setup is built, several experiments were performed to test the optical characteristics of the ring resonator, under different scenarios. These include temperature control, treatment of chip surface with sodium chloride and glucose solutions at varying concentrations, and lastly chip-surface functionalization for biomarker detection. With these experiments (also validated by numerical simulations), we demonstrate the robustness and reliability of our setup.