The growing demand for scalable biomedical solutions calls for precise, programmable, and cost-effective manipulation techniques at the microscale. While mechanical and magnetic methods have been explored, they often face limitations in flexibility, biocompatibility, or scalability. Optical tweezers offer high precision, but suffer from thermal side effects and complex, expensive setups. Optoelectronic tweezers (OET), by contrast, utilize patterned light to induce dielectrophoretic forces, enabling flexible, energy-efficient, and scalable control of microscopic particles using relatively simple hardware.

To support advanced biomedical research at Delft University of Technology, a fully functional OET platform was developed from the ground up. It integrates a custom transparent photoconductive microfluidic chip with a DMD-based optical system for real-time, reconfigurable actuation. Custom-fabricated PDMS microgear robots were successfully manipulated under varying electrical and optical conditions. Using precise motion tracking and calibration, the generated dielectrophoretic forces were quantified, with peak values approaching 500 pN, and benchmarked against theoretical models and literature estimates.

This research demonstrates that complex-shaped microbots can be effectively actuated within a custom-built OET system, paving the way for future applications in automated diagnostics, single-cell manipulation, and intelligent lab-on-a-chip platforms. By combining hardware innovation with theoretical insight, this work lays a robust foundation for microscale robotics in next-generation biomedical technologies.

Plants have been discovered to emit acoustic signals when experiencing drought stress. These acoustic emissions originate from sudden tension releases in the xylem vessels, which transport water within the plant. The rate at which the plants emit these signals increases in the initial stages of the desiccation process, but will reduce later on. Instead of monitoring these acoustic emissions, drought stress can also be identified by actively sending acoustic signals through the stem. This method is applied by Plense Technologies, who develop sensors that transmit ultrasound signals through the plant stem and aim to identify drought stress in an early stage. This can be used as a tool to improve crop irrigation management. However, knowledge on the vibratory dynamics of plant stems and xylem vessels is lacking due to the complexity of the material and frequency spectra, which makes the identification of drought stress in the stems difficult.

State-of-the-art research shows that stem characterization can be performed through modal analysis using Laser Doppler Vibrometry. This method has been performed on both stems and leaves and has been proven to accurately depict the effective properties of the material. This method is suitable for obtaining the vibratory dynamics of the bulk material of the stem, while the acoustic measurements can be implemented to capture xylem vibrations. In addition, computational modeling of the dynamics of plant stems and xylem vessels has rarely been performed, as observed from the state-of-the-art literature. The experiments using Laser Doppler Vibrometry and acoustics, combined with computation modeling of the stems and xylem vessels, form the research gap of this project.

In this thesis, the desiccation behavior of chrysanthemum stems is identified from its elastic and dynamic properties. Chrysanthemums are one of the largest commercial flowers and were selected for their straight stems and usability in the experiments. Experimental modal analysis was performed on the 38 stem over a period of 3 weeks, using a laser Doppler vibrometer and the acoustic sensor developed by Plense Technologies. The goal of these methods was to obtain empirical data on the vibratory dynamics of the stems and xylem vessels over time, respectively. In addition, the mass and diameters of the stems were captured and used to calculate the density of the stems. These parameters were analyzed to determine whether they show desiccation behavior. The laser Doppler vibrometry method was validated through a 3-point bending test to see whether the eigenfrequency is suitable to derive the elastic properties of the stems. The eigenfrequency and bending stiffness were analyzed to determine whether they are suitable parameters for identifying desiccation. Microscopic imaging of the cross sections of the stems was performed to obtain the diameters of the xylem vessels and to get an idea of the inner structure of the stems. Finally, a desiccation experiment was performed in parallel to the mentioned experiments, where 10 plants were measured for a duration of 6 weeks. The parameters suitable for identifying and monitoring desiccation were the mass, density and bending stiffness of the stems. The diameter and eigenfrequency were observed not to be statistically significant enough to monitor desiccation.

Three computational models were designed to simulate the vibratory dynamics of the stems, with three different geometries. The geometries of the models were a cylinder, an elliptical cylinder and a frustum. An optimization script was designed, which minimizes the error between empirically obtained and simulated eigenfrequencies of the stems and computes the related Young's modulus. This optimization was performed on both the first and second bending modes and from the results it was concluded that the frustum model had the best performance. The Young's moduli obtained from all three models were observed to be statistically significant, indicating that it is a suitable parameter to identify desiccation behavior. The xylem vessels were modeled using computational models designed by Dutta et al., 2022, which were adjusted to be implemented in this study. A section of the data obtained from the acoustic modal analysis contained clipped signals, which could not be used for the analysis. A resonance peak was identified, but could not be determined with certainty to be a eigenfrequency of the xylem vessels, due to the lack of knowledge on this matter. However, it was investigated what type and order of eigenmode it would be if it was a resonance of the xylem. It turned out to be a third-order bending mode and this was simulated, accordingly. The results from the model showed significantly higher eigenfrequencies, related to the third eigenmode. Further research on vessels and vascular tissue is required to improve the results.

Multiple recent events have shown the alarming vulnerability of infrastructure on sea to sabotage. This infrastructure can be monitored and protected with passive sonar systems, which provide a number of advantages over other surveillance methods such as RADAR or active sonar. An overview of different localisation methods suitable for the Dutch littoral zone that perform bearing estimation, ranging or complete localisation on the surface plane is made from methods available in literature. From this overview a proposal is made to select cepstral ranging for further research, as there is a limited amount of literature available on this subject. Experimental data from the Dutch coastal area has been gathered with a RHIB and stationary sensor to verify important parameters for both computation and the ranging environment. An effective cepstral ranging method based on experimental data has been developed, although ranging with tidal effects and SNR mismatch remains somewhat problematic. To compensate for this a novel ray tracing method based on open-source measurements has been developed that offers a significant increase in accuracy while effectively compensating for variations in bathymetry and tide.

A new type of mobility device that functions as both a walker and a scooter is being developed to address some issues of current mobility solutions. Some key design parameters for the scooter mode of this scooter-walker hybrid must be optimized. Through literature, a number of simulated "tests", mostly about safety and manoeuvrability, are developed, and 2100 different possible configurations for the device are generated, with each configuration being rated on the performance for each test using the Analytic Hierarchy Process. Some design parameters tend to affect the test outcomes more, particularly the width of the front of the device and the length. In general, larger dimensions lead to a higher stability, but a lower manoeuvrability. A set of optimized key design parameters is identified, but the methodological framework developed is a useful tool by itself as well.

This thesis explores the challenges of using ultrathin graphene membranes in microelectronic mechanical sensors (MEMS) technology, specifically in the development of MEMS microphones. Graphene, being only an atom thin and one of the strongest known materials, offers promising potential for further miniaturization of MEMS microphones. However, the mass loading effect on the graphene membrane can impact the device’s resonance frequency and bandwidth.To address this issue, this study analyzes the dynamic response of the graphene membrane under different pressures and membrane parameters, such as diameter and thickness. The membranes are fabricated by using chemical vapour deposition, after which the membranes are transferred over a cavity. The measuring setup uses a laser Doppler vibrometer to measure the deflection of the membranes and investigate their dynamic response. Pressure-dependent experiments are performed to measure the resonance frequency of the membrane’s response, and the relationship between the radius, thickness, and resonance frequency is explored. By doing these measurements we explore the effect of air loading to investigate the ultimate performance limits of graphene membranes for microphone application.
The experimental results show a clear presence of the air loading effect and align with earlier models of the resonance frequency with mass loading effects. The thesis validates the accuracy and reliability of the measurements and contributes to the body of knowledge surrounding the topic. The limitations of the study include fabrication imperfections and setup difficulties like a limited bandwidth of the piezo-shaker used for the actuation of the membranes. The assumptions made about limited cavity effects are also discussed. Future research could explore the impact of an added backplate with venting holes for capacitive readout. Next to that, the influence of air loading on the system’s damping could be researched.

In this thesis, the analogy between the special theory of relativity and the dynamics of a laborer is developed in the context of labor economics. At the basis of this analogy stands an individual laborer who cannot supply more than 24$hours of labor in a day. This represents the theoretical limit to the flow of labor services (velocity). We argue this limit is analogous to the speed of light. The development of the analogy continues using hyperbolic functions independent of the demand frame of reference (frame of reference) and dependent on the degree of demand (rapidity) as well as the wage inelasticity (mass). This analogy describes the behavior of an individual laborer, detailing the quantity of labor services (position) and their flow, the wage (momentum) and the causation of changes in the flow of labor services (forces). These dynamics in labor economics are consistent with the theory of special relativity, demonstrating economic engineering principles.

Economic engineering is applied to model an individual laborer using the newly developed analogy. The laborer's supply curve shows that wage inelasticity does not change when a laborer performs more labor. Instead, the nonlinear supply curve is attributed to the difference in a laborer's perception of time (proper time). The perception of time depends on the flow of labor services of the observer, making it possible to observe the labor market from different perspectives, including those of companies and laborers. The laborer's perspective on their supply is visualized on the Poincaré disk, from which occupational compositions and job transitions can be analyzed.

In the semiconductor industry, the demand for a continuously higher throughput puts tough requirements on the force capacity and accuracy of actuators. Reluctance actuators, as a promising alternative to the present state-of-the-art Lorentz actuators, are capable of achieving much higher force densities. On the other hand, reluctance actuators suffer from strong intrinsic nonlinearity, such as the quadratic and position-dependent current-force relation, negative stiffness, and magnetic hysteresis, making accurate control challenging. These nonlinear effects can be much suppressed if, instead of controlling the current through the driving coil, the magnetic flux in the actuator core is controlled. As a preparation step for implementing the flux control experimentally on reluctance actuators, this project aims to design and realise the necessary hardware for flux control implementation, including a reluctance actuator prototype and a test setup, and then dynamically calibrate the actuator for flux measurement and control. More specifically, a hybrid reluctance actuator prototype that is suitable for flux control, as well as a test setup for measuring the position and dynamic force output of the actuator, are designed and realised. Using this setup, relations between key variables of the actuator are measured to enable nonlinear compensation in the current and flux control, and a hybrid flux measuring scheme using a Hall sensor and a sense coil is proposed and experimentally implemented. Although noise in the flux measurement is effectively minimised, the result shows a mismatch in the frequency domain between the outputs of the Hall sensor and the sense coil, where further investigation is needed to improve the feasibility of this approach. Furthermore, a hybrid force measuring scheme is proposed and implemented where errors of the load cell due to high-frequency dynamics of the setup can be compensated using acceleration measurements, leading to a wider frequency range for the force measurement. With the realised hardware and the obtained measurements from this project, the next step in future works would be to experimentally implement the flux control on a reluctance actuator and compare its performance with the standard current control.

Ultrafast ultrasound localization microscopy (ULM) is a super-resolved vascular imaging method that provides a 10-fold improvement in resolution compared to ultrafast ultrasound Doppler imaging. Because typical ULM acquisitions accumulate large numbers of synthetic microbubble (MB) tracks over hundreds of cardiac cycles, transient hemodynamic variations such as pulsatility get averaged out. Here we introduce two independent processing methods to retrieve pulsatile flow information from MB tracks sampled at kilohertz framerates and demonstrate their potential on a simulated dataset. Our first approach filters out ULM localization grid artifacts and successfully recovers the pulsatility fraction Pf with a root mean square error of 3.3%. Our second approach relies on the derivation of the velocity distribution of MBs as observed from a stationary observer. We show that pulsatile flow gives rise to a bimodal velocity distribution with peaks indicating the maximum and minimum velocity of the cardiac cycle. Measuring the locations of these peaks, we successfully estimated Pf with an error of 5.2%. Last, we evaluated the impact of the MB localization precision σ on our ability to retrieve the bimodal signature of a pulsatile flow. Together, our results demonstrate that pulsatility can be retrieved from high framerate ULM acquisitions and that the estimation of the pulsatility fraction improves with MB localization precision.

The use of optical fibres as distributed vision sensor within a contactless handling system is discussed in this study. The three primary light colours and a volume diffuser will be used to detect the edge of an object levitating on an air-bearing table. One building block of a bigger system is used that consists of one receiving fibre in the centre surrounded by three transmitting fibres, with each transmitting one primary light colour. Various experiments were executed to find a range where the object edge can be detected. The transition range for horizontal and vertical movement is found. The backscattering of light within the volume diffuser turned out to be much larger than thought. This backscattering causes a small light intensity range. Also, some disruptions in the emitted light caused no logical transition ranges. A model is made to see what happens to the transition ranges when the disruptions are eliminated. The red transmitting fibre is investigated to see the individual contribution to the light intensity received in the receiving fibre. The transition range got from that measurement is translated into the transition range for the green and blue transmitting fibres. Through interpolating the ranges, a total measurement range is found where the object edge can be detected at whatever angle the object is positioned. A bigger system can be made by connecting more building blocks. The proposal for future research is to investigate the positive or negative effects of connecting multiple building blocks.

Electret transducers utilize the electric field generated by an electret, a dielectric with a quasi-permanent embedded charge, to induce charge on an electrode. When the electret is moved relative to the electrode, the induced charge magnitude on the electrode changes, generating a current that can be used to convert mechanical energy into electrical energy. Micro-electret transducers are promising alternatives to conventional electromagnetic transducers for small-scale energy harvesting as they can achieve a high voltage output at low frequencies, can be miniaturized effectively, and can be manufactured using microfabrication methods.

One-dimensional electrostatic models have been developed to predict the power output of electret transducers. However, for micro-electret transducers, fringing fields play a large role in the electrostatic domain. To be able to more accurately predict the output characteristics of micro-electret transducers, a two-dimensional (2D) electrostatic model is proposed. To verify the 2D model, a novel micro-electret transducer is designed. The novel electret design allows the micro-electret transducer to embed charges of only one polarity, increasing the power output of the electret transducer.

The novel 2D model more accurately predicts the power output characteristics of the micro-electret transducer with the voltage output deviating 57%, compared with 317% by the conventional model predictions. Furthermore, the novel unipolar micro-electret transducer achieves double the power output and better charge stability compared with conventional electret transducers.

Nanomechanical resonators with low dissipation rates are ideal tools in fundamental science applications. They have been used in the field of cavity optomechanics for example in ground-state cooling, and in sensing applications, such as atomic resolution mass sensors. Their great sensitivity is due to their high Q-factor, which is a metric that shows how fast a system loses its energy. In ultra-high Q nanomechanical resonators, energy loss is limited to intrinsic and radiation losses, the latter is due to energy dissipation from the resonator into the substrate. Experiments have shown that the Q-factor of resonators with thin substrates are limited by radiation loss. However, the precise role of the substrate remains a topic that has not received much attention, but has significant implications for how we design nanomechanical microchips. Here we show that the resonator mode can couple to nearby substrate modes, which reduces the Q-factor. We found that the strength of this mode-coupling depends on the mode-shape of the substrate, with stronger coupling at anti-nodes of the mode-shape and hardly any coupling at the nodes. Furthermore, we show that clamping down the substrate with double-sided tape reduces the Q-factor of the resonators, this is explained by a reduction in Q of substrate modes due to the tape. Lastly, we found that in thin substrates, which have a higher density of modes, the Q-factor can be limited due to mode-coupling with the substrate. Our results demonstrate that the substrate choice, as it can strongly affect the Q-factor of resonators, should become an integral part of the resonator design phase. These results can likely be used by all types of nanomechanical resonators limited by radiation loss. We can use this knowledge to design chips with resonators that have an even higher Q-factor.

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.

A pacemaker runs on a conventional battery that lasts for approximately 6-12 years, after which the pacemaker must be replaced. Converting the heart wall vibrations into electricity through a vibration energy harvester has been considered a promising solution to this problem. However, the complexity of the heart signals on which the energy harvester has to operate is a challenge. The human heart signal is a broadband signal, consisting of a varying acceleration amplitude at low frequencies. Most of the testing signals used in the labs are harmonic signals, Gaussian white noise or Gaussian coloured noise. These signals do not have the same characteristics as a human heart signal. In addition, the dynamical behaviour of an energy harvester differs per input signal. Therefore, it is important to test energy harvesters on the operation signal, in this case human heart acceleration signals. A heart signal differs per person depending on, for instance, someone's age, sex and health. This means that multiple human heart input signals are needed. Ethical requirements make the measurement of these signals with the necessary details a challenge in itself. In order to meet this demand and to avoid this ethical issue, a heart signal generator is developed as a first step towards the testing of energy harvesters on an approximation of human heart signals. Three different sources of heart signals are combined in order to obtain a new source of heart signals, an approximation of reality, which can be used for the testing. Speckle Tracking Echocardiography signals, open-chest pig heart acceleration signals and human chest motion acceleration signals are analysed and their characteristics are used as the source for the heart signal generator. This heart signal generator is able to mimic multiple heartbeats and the influence of the heart rate on the amplitude and signal duration. The disadvantages of accelerometer measurements are compensated with the advantages of Speckle Tracking Echocardiography measurements, and vice versa, in order to obtain an accurate and detailed heart signal. The output of the heart signal generator is a one-dimensional acceleration signal. An energy harvester is tested on multiple generated heart signals for a heart rate range of 120-200 bpm. It was observed that the mean power output and the efficiency of the energy harvester differs per heart signal. This shows that testing on multiple heart signals is crucial in order to validate that enough power is generated for charging the battery.

Vibration energy harvesting can become a durable source of energy for wireless
sensors or other low power applications like pacemakers. Huge savings in ecological footprint, production and maintenance costs can be achieved by replacing batteries for vibration energy harvesters. Most of the time, newly developed energy harvesters are tested in a lab environment on an electrodynamic shaker. The problem is that the standard lab experiments in the form of a sinusoidal or Gaussian noise signal excitation are not representative for the real world applications. In a classification of ambient vibrations it was observed that most vibrations found in the real world consist of a series of dominant frequencies, shocks and noise. It was also seen that among real world vibrations, there is a lot of variation in the power distribution among the classes. In the aim to bring the vibration energy harvester performance tests closer to the real world applications, an experimental benchmarking of energy harvester performance has been conducted. An energy harvester is designed and applied in the real world on the engine of two different cars. Successively, three different lab experiments are performed on an electrodynamic shaker, each experiment with its own type of vibration control. It is found that only taking the FFT data of a real world vibration is not sufficient. Using a sinusoidal excitation matching a single amplitude and frequency, or even a noise excitation matching the entire power spectrum, results in an under or overestimation of 50% compared to the real world performance. Therefore, to accurately predict the performance of an energy harvester in the real world, simulation or experimental testing need to be performed on the actual or a replication of the intended real world vibration.

Production and manipulation of microdroplets is an active are of research. The demand for finding new ways to produce microdroplets has resulted in a challenge to characterize these droplets. The problem becomes especially difficult for microdroplets which are placed on a transparent hydrophilic substrate. Ink-jet printing, Digital microfluidics, DNA synthesis are some of the applications which need topography measurements of low contact angle microdroplets. One application which is of interest is the sample preparation for Cryo Electron Microscopy (cryo-EM). A recent development in the search for efficient sample preparation for cryo-EM is to use hollow microcantilevers (HMC). HMCs can isolate even a single sub-cellular component and help prepare samples confined in a femtoliter droplet. These droplets are dispensed on a hydrophilic Electron Microscopy grid (EM-grid). By controlling the thickness of the water layer on the EM-grid through evaporation, it is possible to make the HMC technology more reliable by reducing sample wastage. However, such a control loop is absent. A real-time topography measurement of such droplets can serve as a control signal which can be used as feedback for a control loop. The objective of this project is to investigate the feasibility of optical methods to measure the topography information of a low contact angle microdroplet. The scope of this project is limited to develop a tool for a droplet which is supported by a glass slide (droplet-on-glass). In a subsequent study, the tool will be tested for droplets supported on grid (droplet-on-grid). An optical interferometry setup is proposed as a solution. A Mach-Zehnder interferometer is built to obtain the experimental fringes. A Single Frame Fourier Transform technique was used to analyze the data and obtain the results. Droplets of glycerol were dispensed on a glow discharged glass slide. Topography of the droplet was obtained until complete evaporation and a detection limit of 165nm was achieved. The accuracy of the method was found by comparing the results obtained with a Bruker White Light Interferometer (Bruker-WLI) in Phase Shifting Interferometry mode. An accuracy of 23\% was observed. The proposed setup had a repeatability of 14.7nm. To measure the reproducibility of the setup, a 3d printed structure which had the same size and shape as that of a droplet was used. The reproducibility of the setup was found to be 19.8nm over three days. Simulations were performed to analyze the effect of filter shape, filter width and the carrier frequency. Based on these findings, steps to measure a droplet-on-grid system with the proposed setup is explained. Further, to test the capabilities of the instrument the evaporation of a large water droplet on a EM-grid was observed using the proposed setup. It was found that the motion of fringe pattern as the droplet evaporates could give a good indication to control the evaporation time of even conventional machines, which do not employ hollow microcantilevers to dispense small droplets. However, final validation of the proposed setup with the cryo-EM is yet to be performed due to time constraints. As a recommendation for future work, new ways of dispensing samples on the EM-grid are explored. The necessary steps required to validate the setup with a cryo-EM are explained. Further, some ways in which the analysis time could be reduced are explored. This will be helpful in developing a software necessary to implement a real-time solution.

The application of Modal Derivatives (MDs) in conventional reduction methods is an effective method to capture geometric nonlinearities in Finite Element Models (FEMs). Reduction methods, in general, are used to effectively reduce the number of unknowns in FEMs for the sake of computational efficiency. We investigated the applicability of three MDs-based reduction methods in parametrically excited and parametric resonating structures, the focus lays on the steady-state responses. Benchmark in this project is a mechanical Frequency Divider (FD) that consists of cascading mechanical components, each of which is excited by the preceding one by means of parametric resonance. After full activation of the FD, a frequency division along the array of resonators is achieved with a factor 2^i at resonator i. The modularity of the FD makes it an excellent candidate for testing the application of component mode synthesis, where each substructure of the cascade is independently reduced and connected to other members via common interface.