Miniaturized resonant sensors can reach exceptional resolution, but their reduced mass also makes them more vulnerable to frequency noise. In many state-of-the-art devices, nonlinearities emerge at low oscillation amplitudes, coupling amplitude and resonance frequency, thus, enabling amplitude fluctuations to convert into frequency fluctuations. This amplitude-to-frequency (A-F) conversion limits the frequency stability. Consequently, operation in the linear regime is conventionally preferred, constraining the achievable signal-to-noise ratio, and forming a key bottleneck for further improvements in resonant sensing.
This thesis extends the theoretical understanding of closed-loop frequency stability limits for nonlinear resonator operation and explores how nonlinear effects can be exploited rather than avoided. The work studies two mechanisms in particular: nonlinear damping and parametric resonance. The results show that nonlinear damping can substantially suppress A-F conversion at amplitudes beyond the onset of nonlinearity, and it relaxes the conditions required to benefit from established optimal operating points such as the zero-dispersion and amplitude-detachment points. In addition, the thesis demonstrates that parametric drive can improve frequency stability beyond previously derived limits, indicating a route to enhanced sensing performance. ... Read more

This thesis focuses on the development and characteristics of a resonant sensor based on MEMS, which is used for real-time measurement of blood viscosity. The research mainly concentrates on the non-Newtonian fluid behavior related to immediate medical diagnosis. To understand the rheological properties of human blood, including its shear thinning characteristics, Preparation of blood mimicking fluid,we conducted a comprehensive literature review. Based on these insights, we prepared a  blood blood mimicking fluid using xanthan gum and a water-glycerol mixture to replicate the shear-dependent viscosity observed under physiological conditions. The sensor operates by monitoring the changes in its resonant frequency and quality factor when interacting with the fluid, and captures the mechanical response through impedance analysis and Doppler vibrometry. The rheological behavior is modeled using the power law method, allowing the extraction of viscosity over a range of shear rates. Experimental results demonstrate the sensitivity of the system to changes in fluid viscosity, verifying its potential for low-cost, compact, and rapid diagnosis in portable or clinical settings. ... Read more

This work explores the periodic poling of x-cut thin film Lithium Niobate (LN) for use in Piezoelectric Micromachined Ultrasonic Transducers (PMUTs). In recent years, LN has demonstrated significant potential for PMUTs owing to its high sensitivity, low noise, and excellent thermal stability. However, state-of-the-art LN-based PMUTs still suffer from low device admittance, posing challenges for readout circuit design. To address this, we propose LN PMUTs using large electrode arrays to increase conductance. To enable large piezoelectric transcuction with such configuration, ferroelectric domain engineering on thin-film LN is needed. COMSOL simulations were performed to optimize electrode geometry and insulation requirements, ensuring sufficient electric field strength for domain inversion without dielectric breakdown. Structures were fabricated using standard cleanroom techniques, with Silicon Dioxide as the passivation layer. High-voltage pulses were applied using a precision source measure unit, and domain inversion was confirmed through the observation of characteristic current spikes. Our results demonstrate the feasibility of periodic poling using top-side overlapping electrodes, and show increased material conductivity post-poling, consistent with domain wall formation. This approach enables the future fabrication of PMUTs with improved performance using periodically poled Lithium Niobate. ... Read more

Abstract—Resonant mass sensors are emerging as innovative instruments for particle measurement, which utilize the resonance frequency shifts of oscillatory structures. Micro- and nano-pillars have been adopted as the resonators for the high sensitivity of this mass sensing technique. However, existing frequency measurement methods for micro- and nano-mechanical resonators are mostly based on piezoresistive readouts, which were challenged for the integration of such small structures as submicron pillars. In this paper, aluminum nitride surface acoustic wave (SAW) delay line devices were utilized to investigate the potential for measuring the resonance frequencies of several micro/nano-pillars simultaneously. SAW delay line devices for this resonance measuring application have been successfully designed, fabricated, and tested. Both two-photon polymerized (TPP) pillars and focused ion beam (FIB) deposited pillars have been incorporated into the delay line devices. COMSOL simulations in this work have demonstrated the feasibility of multi-resonance measurements. Small peaks, likely corresponding to pillar resonances, were detected and showed some correlation with the resonances. These results suggest that using SAW delay lines is a promising technique for multi-resonance detection of nanopillar arrays. This work paved the way for high-sensitivity
mass sensor development with effective SAW devices and methods of incorporating pillars. ... Read more

In the rapidly advancing field of industrial technology, the demand for enhanced accuracy in environmental Particulate Matter (PM) monitoring has intensified. The Background Section explores the potential of Micro-Electro-Mechanical Systems (MEMS) technology in developing high-resolution, sensitive, and portable devices for PM mass and size detection. The Second and Third Sections provide an overview of the working principles of various acoustic devices and discuss both conventional and advanced PM sensing methodologies. The Piezoelectric Material Alternatives Section concludes with a comparative analysis of different piezoelectric materials.

Design parameters were determined through simulations, as discussed in Section Five, leading to the successful fabrication of a 95 MHz-412 MHz cross-structure SAW resonator in the TUDelft Else Kooi Laboratory cleanroom, detailed in the Fabrication Section. The change in resonant frequency of the device was measured using a Vector Network Analyzer (VNA) probe station, as outlined in the Measurement Results and Discussion Section. The results demonstrate that the device can effectively detect mass loading surface perturbations generated by a 40 μm diameter, 200 nm  high aluminium column in the detection region, despite its inability to sense actual 15 µm SiO2 particle clusters. Finally, the Reflection and Recommendations Section summarizes the project and offers suggestions for future development. ... Read more

Vespa Velutina is an invasive species of hornet posing a threat to European bees and the native European ecosystem. To deal with the problem, a lightweight transmitter has been designed, along with an automatic direction finding receiver algorithm. This report focuses on the work of the "transmission and reception of an ultra-low power signal" subgroup, namely the signal, antenna and amplifier designs. This part of the project ensures that the available ultra-low power signal sent out by the transmitter reaches the receiver with maximum feasible efficiency. ... Read more

The Vespa velutina, an invasive hornet species originating from Southeast Asia, has significantly impacted biodiversity in Western Europe, particularly threatening local insect populations and beekeeping industries. This thesis presents the design and development of an ultra-lightweight tracking device to locate and eradicate Vespa velutina nests, thereby mitigating their ecological and economic impact. The project was divided into three subgroups focusing on different subsystems of the project. The primary objective was to create a tracking system that is lightweight, cost-effective, and capable of transmitting a stable signal over a well known distance. The transmitter design utilized a Surface Acoustic Wave (SAW) resonator-based oscillation circuit operating at a frequency of 433.92 MHz, chosen for its frequency stability and efficiency. The MS412FE battery is discussed to power the system, selected for its low weight and adequate discharge current. The Atmel ATTiny9 was implemented to modulate the signal using ON-OFF Keying, ensuring minimal power consumption and weight. Extensive simulations and testing were conducted to validate the design, ensuring the desired performance metrics. The final tracking device weighs less than 250 mg, operates within a license-free frequency band, and has a signal range meeting the 500 meters requirement in open field conditions. The results demonstrate the feasibility and effectiveness of the designed tracking device in locating Vespa velutina nests. This system can be a solution for environmental agencies and beekeepers to keep the Vespa velutina population under control, preventing any further damage to the biodiversity. ... Read more

This thesis investigates the usage of automatic direction finding in the Asian Hornet tracking field. A lightweight and portable design with a precision of 0.5 degrees is discussed and implemented. The goal of this localization system is to track the transmitter that is attached to the Asian Hornet. The system utilizes two Software Defined Radio (SDR) dongles from the brand RTL that receive the transmitted signal from the transmitter and send it to the computer. The Angle Of Arrival of the signal is calculated using phase interferometry. The results show that the Python program, the algorithm implementation in combination with the used hardware, used to calculate the phase difference is not fast enough to process the received signal in real time. Furthermore, the chosen RTL SDR dongles cannot be synchronized easily which leads to unknown and varying phase differences when receiving the signals. ... Read more

Piezoelectric micromachined ultrasonic transducers (PMUTs) are commonly employed in applications such as medical imaging and gesture recognition. One important performance metric for PMUTs is the quality factor. However, once fabricated, PMUTs have fixed parameters, making them non-tunable for adaptation to various scenarios. This paper presents a technique for using feedback circuits to regulate the bandwidth and quality factor of PMUTs, thereby broadening the potential applications for fabricated PMUTs. First, the electrical characterization of a ScAlN-based PMUT was implemented to extract the parameters in the Butterworth-Van Dyke (BVD) model, which was used in the circuit
design simulations.
Second, the circuit was designed to control the quality factor and bandwidth, simply by adjusting variable resistors in the feedback loop. The characterization results of PCB validated the function of the design. The difference with simulation results was analyzed. Finally, the ultimate performance of the circuit was characterized by a wire-bonded PMUT. The results show that the proposed circuit design effectively manages the Q-factor from 279 to 576 in the quality factor increasing circuit, and 279 to 180 in the quality factor decreasing circuit.
... Read more

Micropumps are essential for providing controlled fluid dynamics in Organ-on-a-Chip (OoC) devices. Additive manufacturing builds up prototypes in several hours with a free-geometry advantage. Therefore, this master's thesis investigates the utilization of additive manufacturing to produce a micropump with a flowrate in the range of several $\mu l/min$ for OoC applications. A ball valve-based piezoelectric micropump was fabricated with a mSLA 3D printer. This micropump generates unidirectional flow through the reciprocating motion of the piezoelectric actuator and the movement of a ball within the conical channel. The virtual mass due to the inertia of the fluid inside the chamber shifts the resonance frequency of the piezoelectric actuator from the 1600 Hz to 43 Hz. The maximum flow rate of $26.5 \mu l/min$ was generated when the applied sinusoidal voltage was 240 Vpp at 5Hz and the maximum back pressure of 36.5 mbar was obtained under this power supply. These results confirm that additive manufacturing provides a promising option for miniature pump manufacturing. ... Read more

This thesis presents a 48V-to-1V 10-level dual inductor hybrid converter (DIHC) containing 11 on-chip switches and an off-chip Gallium Nitride (GaN) switch. Thanks to the 10-level Dickson switched-capacitor (SC) circuit, most of the voltage stress will be taken over by off-chip capacitors, which reduces the voltage stress of each switch to 4.8 V and takes full advantage of the voltage pressure on the 5-V on-chip transistors. This proposed structure is implemented in a 0.18-μm BCD process to convert 48-V input to 1-V output with up to 18-A current load. The post-layout simulations show that a peak power efficiency of 90.6% can be achieved at 5.2-A loading and the power density is about 2093 W/in3 considering the power stage volume.
This thesis also proposes a 48V/3V multi-resonant DC-DC converter for data center applications, consisting of a 3Φ-SC stage and a 4-to-1 series-parallel stage. Thanks to the multi-phase resonant operation mode, the converter uses fewer components to achieve the same voltage conversion ratio as the conventional two-phase SC converters, and can further improve the efficiency by realising soft-charging. This topology is simulated in cadence spectre, and achieves a peak efficiency of 96.94%, and 95.0% full load efficiency at 30-A load. ... Read more

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. ... Read more

Over the past decades the diamagnetic effect has been used for a variety of applications. This ranges from levitating a living frog to stabilizing a force sensor, designing an acceleration sensor and determin­ing the power of a laser. Diamagnetic levitation is the only method in which a passive stable levitation of an object can be achieved. Such a stable levitation has the benefits that the levitated object is iso­lated from its environment, thus eliminating mechanical damping and friction. Furthermore, no energy or control mechanisms are needed to sustain the levitation and to keep the object in its place. With the decrease in the damping, due to the elimination of the mechanical damping component, potential non­linearities in the movement of the plate can present themselves. Such nonlinearities can be exploited in, for example, energy harvesters. In such energy harvesters, the nonlinearities can be used to increase the range of frequencies at which energy can be harvested. As both diamagnetism and nonlineari­ties have their benefits, this study aims at investigating the nonlinear behaviour of a diamagnetically levitating plate in the vertical direction. An analytical model has been constructed which aimed at pre­dicting the (non)linear behaviour of a pyrolytic graphite plate, levitating over a 2x2 array of permanent magnets, which is actuated electrostatically. The model is verified numerically using COMSOL and has been used to predict both the static -­ and dynamic behaviour of the plate. Experiments have been conducted to assess the validity of the analytical predictions. It is found that the static behaviour and the linear dynamic behaviour of the plate can be predicted analytically within certain margins. The ana­lytical model indicates that all combinations of the magnetic force and electrostatic forces investigated have a softening effect on the levitating plate. A softening response is also observed in experiments. However, the analytical model cannot perfectly predict the experimental frequency response functions. A possible reasons for this discrepancy might be mode coupling. Overall, the study of the nonlinear dynamics for a diamagnetically levitating plate will help to gain more understanding on its fundamental mechanism and thus pave a way for its wider applications. ... Read more

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.
... Read more

Facioscapulohumeral muscle dystrophy (FSHD) is the third most common muscle disease in the world. No cure has been found for FSHD, and current treatments focus on alleviating the symptoms. The disease is caused by a genetic error in 1/1000 - 1/200 of the nuclei in a multinucleated skeletal muscle cell. Studying that specific nucleus, by removing it from the cell, perform transcriptomics on it and determining the cell viability after the nucleus removal, can provide important information about FSHD.

In this work, a multiscale 3D printing approach was optimized to fabricate a microfluidic atomic force microscopy (AFM) cantilever that can remove a nucleus from a living cell. With the device mounted on an AFM system, cell experiments were performed, which showed that the nucleus can be removed from a cell using 3D printed microfluidic cantilevers. The printing methods can be used to fabricate various types of suspended microfluidic devices to perform single-cell biopsy and biophysical characterization of single-cells. ... Read more