Vagus nerve stimulation serves as an approach to manage drug-resistant epilepsy. Focused ultrasound stands out as a unique tool, offering a non-invasive modality for VNS. With its excellent depth of penetration and sub-millimeter focusing capabilities in soft tissue, ultrasound allows for precise targeting of the vagus nerve without the need for surgical intervention. This technology relies on piezoelectric transducers that convert electrical energy into ultrasonic waves. However, the high costs and technical difficulties associated with the production of these arrays have led to limited commercialization of piezoelectric transducer arrays. This thesis investigates the design, fabrication, and optimization of a small, low-cost phased-array piezoelectric ultrasonic transducer. The transducer is specially designed for non-invasive UVNS applications in the form of a small patch for the neck. The research is dedicated to the fabrication of the transducer array, designing a transducer capable of both transmitter (TX) and receiver (RX) functions, which in the future can be used for simultaneous image-guided neural regulation. Two prototypes were fabricated: one is a 256-element 2MHz rectangular transducer array integrated into an 8-layer stacked rigid printed circuit board (PCB), and the other is a dual-frequency array integrated into a 4-layer flexible PCB substrate, explicitly designed for simultaneous imaging and neural modulation. The study utilized two key materials, the well-known PZT and the lesser-known but promising <001> oriented PMN-0.3PT piezoelectric single crystal. Through extensive optimization, air-filled PZT transducer arrays were realized, and the cutting parameters for PMN-PT were significantly improved. A unique aspect of the fabrication was the use of flip-chip technology to directly integrate the air-filled 2D array onto the PCB, a method seldom detailed in existing research. While exhaustive testing on phase-delayed beam-forming and imaging capabilities could not be conducted due to equipment limitations, preliminary evaluations of the capacity to generate plane waves were made. The properties of the bulk PZT and PMN-PT transducers were characterized. It was observed that the PMN-PT transducer generated significantly lower ultrasonic pressure compared to the PZT transducer, which aligns with expectations due to the fragile nature of PMN-PT. The first prototype of the PZT array transducer was successfully fabricated and assessed, achieving a pressure of 176 kPa at its 10 mm natural focal point. Subsequently, the internal array second of the prototype was fabricated and evaluated, registering a pressure of 1.14 MPa at the 1.2 mm natural focus point. The results demonstrate the feasibility of building complex piezoelectric arrays using optimized fabrication methods. This lays the foundation for future prototypes to test beam-forming capabilities and for fabrication of the complete equipment afterwards.

This thesis details the design of a selection operator used in a Genetic Algorithm. The Genetic Algorithm is used for loudspeaker filter design of three way loudspeakers for which tournament selection was chosen as selection operator. A methodology is proposed and used to tune the parameters of tournament selection, which is based on diversity and fitness of the population. Besides basic tournament selection, two new adaptive selection operators based on tournament selection are proposed to improve its functionality. The first adaptive selection operator uses noise proportional to the fitness variance of the population to improve the efficiency of the genetic algorithm. The second adaptive selection operator uses a convergence stage to speed up the convergence towards the optimal filter. After the presented tuning process in this thesis, the latter adaptive selection operator was found to perform better. The optimal selection operator and parameters found in this thesis will not translate to every application, because they heavily depend on the design and the application of the genetic algorithm. However, the presented comparison of selection operators, the provided performance metrics and design methodology can still be used to guide the choice and the tuning process of a selection operator used in any genetic algorithm.

The current drug development process is a costly effort both in terms of budget and time. Organ-on-Chip (OoC) technologies are rapidly developing and are used for various applications and studies that aim to reduce the costs of this process. They represent the convergence between tissue engineering and microfluidic technology to provide researchers with an in vitro tool that can better recreate the environmental conditions in which cells would normally develop in vivo. One of the applications of this tool is the implementation of such platforms to study heart and muscle tissue. Electrical stimulation of this tissue is of great importance for these studies. There exist different ways in which these cells can be electrically stimulated such as microelectrode arrays (MEAs) or external electrodes. These methods pose several challenges that need to be addressed. The scope of this project is to implement 3D microelectrodes into an already existing device from the company Bi/ond to electrically stimulate the cells developing inside. This approach aims to solve the existing challenges in current methods for the electrical stimulation of tissue. This project succeeded in developing such 3D microelectrodes although the functionality of the device could not be proven. However, several approaches were also studied and propositions were made on how to continue with this project.

Purpose The main purpose of this report is to find out whether the OpenBCI "Ultracortex Mark IV" Electroencephalogram (EEG) headset is capable of differentiating EEG-signals of motor execution from neutral state with recorded data and to find out whether it can differ motor executions between left and right hand. Next to that, it is to be determined whether the OpenBCI headset was the optimal one for this purpose. Method First, the specifications of different headsets were compared. Afterwards, a montage of the electrodes was designed to detect motor execution and motor imagery, mainly centered around the locations C3, Cz and C4, on the top of the scalp. The software "Openvibe" was used to extract data from the headset during experiments and to record it in a csv file. A subject was asked to follow a video with a sound cue followed by a visual cue instructing to move either its left hand or right hand. Result Merging the left and right hand trial data together, the result is that the headset shows in the alpha band (7-12 Hz) mostly a decrease (ERD) in magnitude around the visual cue, sometimes followed by a bigger increase in magnitude (ERS). Looking at the extremes after the cue, it is seen that mostly the difference in magnitude is around a factor 1.5 compared to the average magnitude of before the visual cue. Splitting the trial data between left and right hand, similar results can be seen, but one hand produces slightly more ERD or ERS than the other hand depending on the position of the electrode on the left or right hemisphere of the brain. Conclusion The OpenBCI headset can in fact detect a difference between movement of the hands and the neutral state. Differentiating between the movements of left and right hands seems possible from the results, but the difference in the signal of left and right hand is minimal. It is recommended to repeat the experiment with more trials and different subjects to get a more solid conclusion.

Tissue vitality monitoring is a crucial process to preserve patients’ health during post-surgical recovery or to ensure full adaptation and healing of transplanted organs. Among the many local factors for vitality assessment, tissue oxygenation gives an insight into entire tissue recovery and is directly linked to cell metabolism. To be able to assess oxygenation at the cellular level, NADH fluorescence sensing is used due to its contribution to the cellular respiratory cycle and high sensitivity to oxygen concentration. The current devices for NADH fluorescence sensing are limited to external measurements, where they are suitable for hospital use. This raises the need for a device that is implantable and bioresorbable so that it can stay in the body after the surgery and does not require secondary surgery for removal that puts the patient at risk. The goal of this master’s thesis is to introduce the design of a bioresorbable optical filter and photodetector for the measurements of oxygen through the detection of NADH fluorescence. The design consists of an absorption layer, a Fabry-Perot filter, and a wavelength-specific photodetector; where the overall response is designed to have high sensitivity to the emission wavelength of NADH (470nm) and low sensitivity to the excitation of NADH (350nm). ZnO nanoparticles are chosen to be the absorption layer due to their high absorption properties to 350nm and biodegradability, where the optical response is then tested through spectroscopy measurements. For the Fabry-Perot filter, a design with SiO2 and SiNx layers has been created with simulation and tested with optical measurements. The complete design consists of 15 layers and has a total thickness of approximately 1μm. Lastly; for the photodetector, Spectra simulations have been conducted for the determination of the optimal design properties. The choices are then adapted to a mask design for the fabrication, in which the back side etching of the silicon wafer is required for biodegradability and optical performance. The fabrication of the photodetector has not been completed due to the time frame of the project. The measurements on the combination of ZnO and Fabry-Perot filter show that the transmission of 470nm is 2.5-4 times larger than the transmission of 350nm, which is expected to increase to at least an order of magnitude when combined with the photodetector. For future experiments, it is recommended to conduct more tests on the filters and ZnO to ensure repeatability and consistency.

Tissue vitality monitoring is a crucial process to preserve patients’ health during post-surgical recovery or to ensure full adaptation and healing of transplanted organs. Among the many local factors for vitality assessment, tissue oxygenation gives an insight into entire tissue recovery and is directly linked to cell metabolism. To be able to assess oxygenation at the cellular level, NADH fluorescence sensing is used due to its contribution to the cellular respiratory cycle and high sensitivity to oxygen concentration. The current devices for NADH fluorescence sensing are limited to external measurements, where they are suitable for hospital use. This raises the need for a device that is implantable and bioresorbable so that it can stay in the body after the surgery and does not require secondary surgery for removal that puts the patient at risk. The goal of this master’s thesis is to introduce the design of a bioresorbable optical filter and photodetector for the measurements of oxygen through the detection of NADH fluorescence. The design consists of an absorption layer, a Fabry-Perot filter, and a wavelength-specific photodetector; where the overall response is designed to have high sensitivity to the emission wavelength of NADH (470nm) and low sensitivity to the excitation of NADH (350nm). ZnO nanoparticles are chosen to be the absorption layer due to their high absorption properties to 350nm and biodegradability, where the optical response is then tested through spectroscopy measurements. For the Fabry-Perot filter, a design with SiO2 and SiNx layers has been created with simulation and tested with optical measurements. The complete design consists of 15 layers and has a total thickness of approximately 1μm. Lastly; for the photodetector, Spectra simulations have been conducted for the determination of the optimal design properties. The choices are then adapted to a mask design for the fabrication, in which the back side etching of the silicon wafer is required for biodegradability and optical performance. The fabrication of the photodetector has not been completed due to the time frame of the project. The measurements on the combination of ZnO and Fabry-Perot filter show that the transmission of 470nm is 2.5-4 times larger than the transmission of 350nm, which is expected to increase to at least an order of magnitude when combined with the photodetector. For future experiments, it is recommended to conduct more tests on the filters and ZnO to ensure repeatability and consistency.