This report discusses the design and implementation of a wireless network to demonstrate a dynamic process based on the Susceptible-Infected (SI) model. The system supports up to 10 nodes that communicate over Bluetooth Low Energy (BLE) and employ a token passing based network protocol. The Relative Signal Strength Indicator (RSSI) is used to determine whether connections are formed depending on distance. Each node displays their SI state and to which sub-network they belong through an RGB LED. Furthermore, a centralized visualization system is used to combine this information to provide an overview on a screen. The data for this visualization tool is collected by a visualization node that scans the network and copies the communicated data packets to the visualization script. The data is communicated to a webpage using a WebSocket, this webpage is hosted on a local host and displays an interactive, continuously updating network plot. The model can be initialized through this interface as well. Experimental evaluation shows that the system successfully reproduces the expected probabilistic behavior of the SI model across the implemented network topologies. The prototype operates on battery power with an estimated runtime of approximately 34 hours per node. ... Read more

Uncovering the formation history of dusty star-forming galaxies in the early universe requires wideband spectroscopic instruments capable of detecting redshifted emission lines in the millimeter and submillimeter regime. The on-chip spectrometer DESHIMA 2.0 addresses this by integrating filterbanks and kinetic inductance detectors (KIDs) onto a single chip, enabling wide frequency coverage in a compact footprint. However, performance is currently limited by losses in the dielectric layer of its microstrip lines, which reduce transmission efficiency and sensitivity. Minimizing these losses is crucial not only to enhance signal throughput but also to enable the use of parallel-plate capacitors (PPCs), which significantly reduce resonator size, increase detector count, and thus improve spectral resolution. Achieving low-loss dielectric films is therefore essential for the next generation of high-resolution spectrometers such as TIFUUN.

To support this development, this thesis focuses on optimizing the deposition of hydrogenated amorphous silicon (a-Si:H) films using Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICP-CVD). These films function as dielectric layers in both microstrip lines forming the filterbank (90–360 GHz) and in PPCs (1–10 GHz).

Since direct measurement of dielectric losses was beyond the scope of this project, optimization was based on properties known to correlate with loss mechanisms—namely two-level systems (TLSs) and absorption in the vibrational tail. TLSs are expected to dominate at PPC operating frequencies, while vibrational absorption is more relevant in the filterbank. The optimized properties include residual stress, thickness non-uniformity, optical and infrared refractive index, band gap, void-volume fraction, hydrogen content, and microstructure parameter.

A Taguchi L18 orthogonal array was used to systematically vary seven deposition parameters: table temperature, silane flow rate, ICP power, table RF power, gas ratio (silane/argon), pressure, and native oxide removal method (argon milling vs HF dip). Film properties were evaluated using ellipsometry, FTIR spectroscopy, and a stressmeter.

ANOVA revealed table RF power as the dominant factor, with the highest contribution to five of the eight properties: thickness uniformity, refractive index, hydrogen content, microstructure, and residual stress. In the latter, increasing power shifted the film from tensile to strongly compressive regimes. Other parameters had more moderate effects: chamber pressure had strongest influence on void-volume fraction and infrared index, while silane flow rate and wafer preparation affected the band gap most significantly. Despite some models exhibiting high residuals, indicating unmodeled interactions between the parameters, the overall analysis successfully identified key relationships between the deposition parameters and the material properties.

Two optimized recipes were selected using Grey Relational Analysis, with equal weighting assigneds to hydrogen content and void-related properties. Recipe 19 achieved minimal hydrogen content (4.3 at.%) and low residual stress, making it a strong candidate for minimizing dielectric losses in the filterbank. However, it also showed high void fraction and surface inhomogeneity. Recipe 20, aimed at maximizing hydrogen content, reached 16.3 at.% but showed only average performance and suffered from high compressive stress (–745 MPa). As a more robust alternative, Recipe 9 offered low void content, moderate hydrogen level, favorable stress (+125 MPa), and good uniformity—making it the most practical candidate for integration into both filterbank and PPC structures.

Future work should focus on direct measurement of dielectric loss tangent and TLS density under cryogenic conditions to validate the predicted performance in superconducting spectrometers. ... Read more

In the quest to create a 3D map of the universe, TU Delft recently started research on a Terahertz Integral Field Unit with Universal Nanotechnology or TIFUUN. These integral field units contain up to 217 spectrometer pixels (spaxels). Kinetic inductance detectors (KID) are dominating the area coverage of a spaxel. Reducing their size, allows for more spectral channels (called voxels), resulting in a higher spectral resolving power. A new type of KID showed up, which incorporates a parallel plate capacitor with a dielectric layer, significantly reducing the required space per component compared to the current state of the art. The performance of this capacitor is compromised by two-level system (TLS) noise in the dielectric layer. Previous literature made suggestions on what material characteristics influence TLS noise, called TLS indicators. These dielectric layers, in this case a-Si layers, are deposited in a plasma inside of an inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) machine. Plasma emission spectra were collected, using a spectrometer and an optical fiber, during the deposition of different recipes to investigate how the plasma spectrum is related to the room temperature (RT) TLS indicators of a-Si films. Voigt profile fits were made through key emission peaks in the spectral data. The ratios between the heights of the key emission peaks in the spectral data were compared to the TLS noise indicators. No statistically significant relation was found between these ratios and TLS noise indicators. These results suggest that the plasma spectrum during film deposition is unrelated to RT TLS indicators of a-Si films. This narrows the focus for future research to other factors influencing these indicators, bringing us closer to creating low TLS noise dielectric films. ... Read more

This project reports the design and validation of a wheeled mobile robot that collects spatially distributed environmental data inside a building. Built on the four-board GEMS stack—Sapphire (communication), Ruby (sensing), Diamond (motor control), and Emerald (power), the prototype integrates a CAN bus backbone, an I2C sensor backplane, ultrasonic obstacle detection, and a Wi-Fi web interface. Responsibilities were divided among three subgroups. The wireless team implemented the CAN network, web server, and finite-state machine for autonomous navigation. The mechanical team designed and printed the chassis; they also developed battery management and voltage regulation. The motor control group implemented the PI control. Integration tests show that the system satisfies every “must-have” requirement in the Programme of Requirements: CAN frame loss remained below 1 % during a five-minute run, Wi-Fi throughput exceeded 1 Mbps in the range of ten meters, ultrasonic sensors detected obstacles from 10 cm to 30 cm and temperature and humidity data were logged at 2 Hz with millisecond precision. However, late delivery of prefabricated cabling forced a temporary hand-wired CAN harness, leaving room for mechanical refinement. Overall, the project demonstrates that the open-source GEMS [10] architecture can be turned into a low-cost, modular sensor platform on wheels, providing a reproducible foundation for future research and classroom exercises in embedded communication, control and data acquisition. ... Read more

This thesis develops a method to map the surface of an exoplanet. The problem of exoplanet mapping sounds easy to solve. Take a few photographs of an exoplanet and sew them together to create a map of the surface. The telescope required to do this is far beyond our technological capabilities. However, our current telescopes could allow us to measure the light reflected from the star on the surface of the star as a point source. This thesis constructs the surface map of an exoplanet using only a point source of reflected light as information. This method of planet mapping is called spin-orbit tomography, introduced by Cowan and Agol [2008] and more in depth by Fujii and Kawahara [2012]. Spin Orbit tomography is a method to construct a surface map from the reflected light curve, the total intensity of the light from the star, reflected on the surface of the planet, directed towards an observer. ... Read more

In the near future, next-generation telescopes will be able to observe Earth-like exoplanets illuminated by their parent stars for long periods of time. As the distance between exoplanet and observer is enormous, exoplanets will only make up a pixel on our image. However, the observed intensity of this pixel will fluctuate over time as the exoplanet rotates about its axis and orbits around its parent star. These fluctuations in the reflected light contain information about the planet’s surface. Previous researchers have developed a retrieval method known as spin-orbit tomography which uses these intensity fluctuations to construct a surface map of the exoplanet assuming fully diffuse reflection as a model for the reflection of starlight. In this thesis, we aim to build on this method by introducing two new reflection models, namely Fresnel and Lommel-Seeliger reflection, and by using this composite reflection model for the starlight we attempt to reconstruct the surfaces of exoplanets based on their observed light curve. We will derive an analytical expression for the observed intensity of the light reflected off an exoplanet. Next, we will simulate intensity observations along the orbit of an exoplanet with a pseudo-randomly generated surface containing terrain types found on Earth.
As we assign a measure of reflectance for each reflection model, we will construct three distinct reflectance maps for one planet, nd simulate the observed light curve by linearly transforming these maps. Afterward, we attempt to retrieve the reflectance maps from the observed signal by inverting the transformation.
We show that the retrieval of all three maps is successful if the light curve is observed without noise, even when the number of samples is low. If artificial shot noise is imposed on our signal, we are still able to retrieve glossy reflectance maps for Lambertian and Lommel-Seeliger reflection by truncating the transformation matrix. Lastly, we show that even if the original light signal originates from an exoplanet that only reflects according to the Lambertian model, then the composite reflection model still retrieves the Lambertian map accurately. On the other hand, if the original light curve is simulated by the composite reflection model, then the Lambertian method does not retrieve an accurate surface map. ... Read more

60 million people around the world have epilepsy, which is a neurological disorder that severely impacts their day to day life negatively. Currently available methods to reduce the effects of epilepsy are either ineffective or require expensive and invasive surgery. A new method has been found that can suppress epilepsy without the need of surgery, called Transcutaneous Vagus Nerve Stimulation (t-VNS). Detecting epileptic seizures is important for this method, as the stimulation should only be used during a seizure. Traditionally, detecting epilepsy is done using scalp-Electroencephalography (EEG), which requires a controlled environment and is hard to use in day to day life. Recently, advancements have been made in ear-EEG, which allows for EEG outside a controlled environment. This study focuses on detecting epilepsy using ear-EEG. Ear-EEG was simulated using scalp-EEG channels close to the ear. After low-pass filtering and downsampling the results were obtained using features obtained from the Wavelet Transform (WT) and Fourier Transform (FT) in combination with several Machine Learning (ML) models; these being a random forest, a Support Vector Machine (SVM), and a Neural Network (NN). Furthermore PCA was also applied to the features, with a threshold of 0%, 95% and 99%. The results clearly show that using the WT outperforms features from the FT. Furthermore, out of the three models, the NN consistently has the best sensitivity for detecting seizures. The best sensitivity was achieved using WT features with a NN and a threshold of 99% for the PCA. The accuracy and sensitivity are 99.3% and 83.5% respectively, which is comparable to previous ear-EEG based research detecting epileptic seizures.
... Read more

In this thesis, we provide a method for reconstructing a planet's surface map from its reflected light curve. We are going to derive an equation for the reflective light-curve under the assumption that the surface map is characterized by four different surface types (ocean, vegetation, sand and snow), is stationary (no clouds), and that all reflection is diffuse (Lambertian). We will show that the transformation is a linear function of the surface map and we will work out the transformation for arbitrary observer inclination and axial tilt. Using this knowledge, we create mock light curve data of self-generated planets. Afterwards, the transformation is inverted using the Moore-Penrose pseudo-inverse and the mock data will be used to demonstrate the surface map recovery for edge-on and face-on observations of planets with different axial tilts. Furthermore, we also provide a method for recovering the planet's axial tilt from its reflected light curve.

Even when a realistic amount of photon shot noise is added to the light curve, we are able to retrieve the planet's surface map and axial tilt fairly well, especially when the planet's tilt has larger axial tilt.

... Read more

Terahertz time-domain spectroscopy (THz-TDS) is an extremely useful method to probe material electrodynamics. The THz regime comprises rich physics, enabling to determine compositional, electronic and vibronic degrees of freedom through THz spectroscopy of a material under study. However, to study nanometre size thin films with THz-TDS, we need to overcome a large mismatch in length scales, since the THz wavelength is on the order of millimeters. A solution lies in the THz probing of metasurfaces, artificial materials made of conductive structures with length scales much smaller than the probing wavelength. Such a metamaterial induces enhanced electromagnetic field strengths near the surface, enabling nonlinear spectroscopy without the need for strong-field terahertz sources. Additionally, they provide sensitivity to the local (micron-scale) electrodynamic environment. In the ideal case, one can infer significant information about the thin film electrodynamics via the resonance frequency and dissipation in the metasurface. This thesis project comprises the optimization of terahertz (THz) resonant electric split ring resonator (eSRR) metasurfaces for enhanced-light matter coupling, suitable for material characterization. Experimental characterization is combined with finite element simulations, to obtain the transmission spectra and near-field electric, magnetic fields and current densities. In simulation, the eSRR design is optimized to obtain an up to four times stronger response at resonance than the designs described in literature. The optimized design is studied on different substrates, revealing the ability to extract a resonance even close to a substrate Reststrahlen band. This thesis concludes with characterization of the metal-insulator transition of transition metal oxide NdNiO3. From the resonance frequency and quality factor it is possible to track this phase transition from time-domain terahertz spectroscopy, thereby revealing the ability to probe extremely thin films, with an outlook on out of equilibrium studies. ... Read more

The increasing number of drones forms a more significant problem every year. Negative impact becomes more apparent during daily life as, for example, airport operations are shut down due to unauthorized users of drones. This report focuses on designing a new wideband antenna array as part of an integrated radar system to detect small objects, such as drones or birds. The design is done by studying generic array design assuming uncoupled antenna elements with omnidirectional radiation patterns. A comparative study of possible antenna element types has been conducted, concluded with selecting the best candidate. An antenna array has been designed with the embedded antenna elements and is verified using a prototype. Finally, an additional enhancement using meta-materials is done in an attempt to improve the antenna’s performance further. A wideband patch antenna array is proposed, which achieves a verified impedance bandwidth of 0.90 GHz with a scanning capability of ±30 degrees in azimuth and ±15 degrees in elevation. The measurements verify what the simulations have shown at broadside. Also, simulations have shown that the impedance could be increased to 2.96 GHz if a smaller feeding pin is used. It is also demonstrated that an AMC ground plane doesn't improve the antenna's performance and is, therefore, not implemented. ... Read more

Microwave Kinetic Inductance Detectors (MKIDs) are remarkable photon detectors, that have single photon detection and energy resolving capabilities in the near-infra red and higher frequency range. At lower frequencies, MKIDs are excellent radiation detectors as well, because of their high sensitivity and natural multiplexing capabilities, which enable large scale detector arrays.In the (near) optical regime, MKIDs can use their single photon energy resolving capabilities for direct exoplanet detection, in missions like Hab-Ex or LUVOIR. This would enable atmospheric characterization, potentially finding habitual exoplanets. However, two aspects of the MKID still need improvement for this application: the photon absorption efficiency must go from 30% to 50% and the resolving power must go from 8 to 100, both for wavelengths of 1 µm. In this thesis, we study the single photon response and generation-recombination (GR) noise in optical NbTiN-Al hybrid MKIDs, to find knowledge gaps and opportunities to improve detector performance. For the single photon response, we set up a model starting from the Rothwarf-Taylor and Mattis-Bardeen equations, including the pair-breaking efficiency as only fit parameter. Both at high (220 mK and 250 mK) and low (120 mK) temperatures, the model predicted the single photon response of 4 different wavelengths correctly, with a fitted pair-breaking efficiency close to expected values (30%-70%), but somewhat high, which might be due to a non-thermal distribution of quasiparticles caused by read power. In particular, the effect of phonon trapping was captured by the model, which was verified by considering MKIDs on substrate and membrane.At lower temperatures (120 mK), a second exponential decay in both the amplitude and phase single photon pulse tail was observed, which is not explained by the model. This second decay was faster for higher read powers. For the GR noise, also an unexpected feature was observed: the GR noise level dropped exponentially, when lowering temperature (<250 mK), for the amplitude, phase and cross power spectral densities (PSDs). High read powers mask this effect, due to the creation of excess quasiparticles. The noise drop was present in all analysed MKIDs, except for an MKID with an 150 nm (instead of 50 nm) thick Al film, which might be due to read power induced excess quasiparticles. When assuming the GR noise to be Poissonian, we show that the behaviour could be explained by a process which limits the quasiparticle lifetime, while keeping the quasiparticle density thermal.We hypothesize the cause of both of these unpredicted measurements to be quasiparticle trapping, which is the localisation of quasiparticles. This process is known to degrade superconducting tunnel junction detectors and limit quasiparticle lifetimes in MKIDs. A secondary ion-mass spectroscopy (SIMS) analysis showed Fe contamination on the substrate-Al film interface, which is thought to be the quasiparticle trapping cause in our systems, consistent with the observation that increasing the film thickness diminishes the GR noise drop. To our knowledge, quasiparticle trapping has not be studied in steady state experiments, such as GR noise measurements.Different models including quasiparticle trapping have been set up and can predict the amplitude PSDs, when assuming that trapped quasiparticles cannot dissipate microwave power. However, comparison of the fitted model parameters with the trapping and detrapping rates calculated by Kozorezov et al., showed a orders of magnitude difference. Combining this with the fact that amplitude, phase and cross PSDs show similar behaviour, implying that they relate to Cooper-pair fluctuations, led us to conclude that the trapping process cannot be the cause of the observed behaviour. On-trap recombination most likely plays a role in the GR noise drop, but models including this process involve cyclic transitions and non-equilibrium steady states, greatly complicating the calculations. The second exponential decay could not be described by the trapping models, but also here on-trap recombination and Cooper-pair fluctuations must be considered.A qualitative analysis on the MKID detector performance (both single photon and radiation power integration) showed that quasiparticle trapping effects can increase the energy resolving power and noise equivalent power at low temperatures, when this effect replaces the usual lifetime saturation due to excess quasiparticles. ... Read more

Mankind becomes ever more reliant on wireless technology like mobile communications, navigation and radar. This development has resulted in more sensitive receivers, but this increased sensitivity also has increased the susceptibility of these receivers to interference from external sources. One of these sources that is known to disrupt terrestrial communications is the Sun. The DISTURB project aims to provide the means to observe and study interference phenomena generated by the Sun between frequencies of 10 MHz and 3 GHz. Furthermore, DISTURB stations should provide the ability to observe the Sun from sunrise to sunset, at any location in the world and thus require full hemispherical coverage. This master thesis project is concerned with the design of a conformal phased array antenna for a novel application in radio astronomy. The goal of this project is to provide an initial conformal array design that is able to provide full hemispherical coverage in the 1500 MHz to 3 GHz band of the DISTURB project. A quasi-spherical array of radius 1.55 metres and with 343 crossed modified bow-tie antenna elements, distributed using a novel geodesic topology, is proposed and found to satisfy DISTURB requirements in the frequency range of 1.3 to 3 GHz. Hence, the designed array is found to achieve a fractional bandwidth of 79% and therefore even exceeds the initial design goal. Finally, the designed array is compared to a parabolic reflector antenna, resulting in an insight in the complexity of a conformal phased array antenna design and the advantages and disadvantages such a conformal phased array antenna may bring to the DISTURB project. ... Read more

The objective of this master thesis research project is to determine the overall polarisation sensitivity of the Near Infrared Spectograph (NIRSpec) on board the JamesWebb Space Telescope (JWST). Understanding the polarisation sensitivity is important to correctly interpret the output data and accurately calibrate the instrument during operational lifetime. As experimental research on this topic for NIRSpec was limited, a numerical code has been built to simulate the light following the optical path of NIRSpec. This numerical code is effectively a ray tracer with polarisation state analysis functions. They ray tracer is designed to be modular, making it straightforward to add new functions or optical elements, either for future work on NIRSpec or application to other instruments. The analyses regarding the polarisation sensitivity were performed in three main categories: the induced polarisation through reflections by mirrors, the grating efficiencies and overall throughput, and the effect on the calibration process. The JWST is a large space telescope that aims to help better understand every time period of the universe from the Big Bang till the present. The launch is currently scheduled in March 2021. The JWST shall provide new data by observing thermal radiation from various celestial objects. It houses four main science instruments, one of which is NIRSpec developed by the European Space Agency. The optical design of NIRSpec is based on three three-mirror anastigmats and six main opto-mechanical assemblies. Two of those assemblies are the grating wheel assembly which houses dispersive reflection gratings and the calibration assemblywhich is used to internally calibrate the instrument. These optical elements introduce a polarisation sensitivity, meaning that the instrument output data will depend on the polarisation state of the incoming radiation. Even though NIRSpec will mainly observe unpolarised light sources, a degree of polarisation will always be induced via reflections by themirrors. The optical path of the calibration beam differs from the nominal science path, so a different degree of polarisation will be induced via the calibration path compared to the nominal science path. Application of the calibration measurements to the science measurements can thus lead to errors on the deduced signals. The induced degree of polarisation for the nominal science path will likely remain below 2%. This degree of polarisation is slightly dependent on both wavelength and initial incidence angle, but not significantly. The analysis of the grating efficiencies clearly indicates a polarisation sensitivity up to 20% for the medium resolution gratings and up to 40% for the high resolution gratings. Due to the low estimated induced polarisation below 2%, the maximumuncertainty in the output data for unpolarised incoming light would be lower than 1%. Observing celestial objects with an inherent degree of polarisation, however, could introduce a significant uncertainty in the measurements. Finally, the calibration process has also been examined and it can be concluded that the induced degree of polarisation by the calibrationmirrors before the light reaches the grating will be 1 to 2% higher compared the nominal science path. Whether or not this difference should be taken into account will depend on the application. Recommendations for future work can be divided into four categories. First, the reflection grating efficiencies should be analysed in more details as the accuracy of the presented results is uncertain. Second, the filters and detector are modelled as single layer Fresnel surfaces, while in reality they consist of multiple layers of different materials. It should be researched how this assumption affects the presented results. Third, configurations using the long-slit spectroscopy and integral field spectroscopy have not been analysed while the microshutter assembly is modelled as ideal transmitter. Analysing these configurations would provide a more complete understanding ofNIRSpec’s polarisation sensitivity. Fourth, validation through measurement data would help determine the accuracy of the ray tracer presented in this master thesis research. This data could come from eithermeasurements of NIRSpec during operational lifetime or comparable instruments of which measurement data is available. ... Read more

Microwave Kinetic Inductance Detectors (MKIDs) are extremely sensitive radiation detectors based on superconducting resonators that can be combined in large arrays on a single readout line within a limited frequency bandwidth. This makes MKIDs ideal detectors for the ultimate far-infrared observatory: a future space-based actively cooled telescope with its performance solely limited by the low universe background radiation. However, to reach these detector requirements, state-of-the-art MKIDs still need a order of magnitude improvement in device sensitivity. In this work, the MKID sensitivity is improved by reducing the aluminium volume that absorbs pair-breaking radiation into quasiparticle excitations, while making sure all radiation is still absorbed. Furthermore, a key requirement is sufficient reduction of excess noise as to keep the device intrinsically limited by thermally driven random fluctuations in the number of quasiparticles in absence of radiation, or Generation-Recombination (G-R) noise. To this end, a model is developed that describes the noise contributions as function of device geometry, readout power, material properties and radiation power. Subsequently, a realistic MKID design is presented and tested that reduces excess noise and maximises the sensitivity, expressed as Noise Equivalent Power (NEP). At high temperatures, good overall agreement is found between the measured noise spectra and the model. At low temperature T = 120 mK, the measurement results give an optical NEP similar to current state-of-the-art MKIDs. The NEP is not as low as expected due to short quasiparticle lifetimes, an unexpected decrease in the G-R noise level and a very high excess noise attributed to Two-Level Systems (TLS) noise that starts to dominate the already low G-R noise spectrum at low temperatures. Possibly, the quick quasiparticle lifetime saturation and noise level drop are caused by a strong readout power effect, as the readout power is known to create excess quasiparticles and to cause a strongly non-thermal electron energy distribution in the aluminium strip of the MKID. However, the exact microscopic details of these effects are unknown and not studied in this project. Based on the current chip design, a straightforward way to improve device performance and study the readout power effect in more detail is a reduction of the high TLS noise levels, which is possibly fabrication related. This would allow an unobstructed view of the G-R noise spectrum at low temperatures, thereby allowing both a study of the readout power effect on the quasiparticle system, and ultimately achieving the improvement in NEP needed reach the detector requirements for the ultimate space-based far-infrared observatory. ... Read more

Superconducting-normalconducting-superconducting (SNS) transmons with 2-facet Al-shell nanowires are qubits compatible with magnetic fields above 10 mT. There are important correlations of the room temperature nanowire resistance with the chance of the qubit being measurable: at a resistance of 2−3 kΩ, the qubit is almost guaranteed to work. The chance of success halves every 2−3 kΩ increase. This information can be used to increase the yield. The flux noise power spectral density (PSD) of a model spin-1/2 fluctuator has been investigated as a function of the magnetic field using the Zeeman interaction. Not only the fluctuations parallel to the magnetic field contribute, but also the fluctuations perpendicular to the magnetic field. Cross-terms cancel out. The flux noise PSD of the SQUID is a linear combination of these spin PSDs when the spins are spatially uncorrelated. The magnetic field suppresses the parallel spin-axis noise PSD contribution as cosh^(-2)(μB/kBT). The magnetic field changes the perpendicular spin-axis PSD contribution due to the Larmor precession frequency peak 2fZ~μB, but does not influence the PSD contribution at frequencies higher that the Larmor precession frequency. When rotational asymmetry in the SQUID geometry is present, the PSD contributions of the perpendicular and parallel components can be separated. In our setup, a perpendicular coil is used to align the magnetic field with the transmon plane. The alignment procedure of maximizing the resonator frequency vs. the perpendicular coil field has been verified. To measure the flux noise, the perpendicular coil is first used to change the flux bias by large amounts. Then a dedicated flux bias is used to make a fine-grained sweep over the flux without flux-jumps, to calibrate the magnetic field at the SQUID. We have found a signal of the flux noise at zero field and at field. A flux noise amplitude of A~1000 μΦ_0 has been found at zero magnetic field. ... Read more

On-chip spectrometers, such as DESHIMA and SuperSpec, require transmission lines with very low loss of tanδ < 10^-4 to achieve sufficient system efficiency. Transmission lines with higher loss would introduce too much signal attenuation in the line from antenna to filter and in the filters themselves. Data regarding the losses of transmission lines at THz frequencies and sub-K temperatures is severely lacking. In this report an on-chip Fabry-Pérot resonator concept is demonstrated that can be used to measure the losses of a transmission line with high sensitivity at high frequencies. To create the in-line Fabry-Pérot resonator, a transmission line of certain length is coupled to a THz source via a twin-slot lens antenna on one side and to an Al-NbTiN hybrid MKID on the other side. The goal of this work is to measure the losses of microstrip lines at frequencies > 300 GHz, at a temperature of about 250 mK, with dielectric dominated loss in the range of 10^-3 > tanδ > 10^-5. There are several experimental challenges for measuring tanδ. The first challenge is the limited frequency resolution of the source, due to which resolving low tanδ can become impossible. Secondly it was experimentally found that there is stray light coupled to the detector which causes a spurious response with a level of −30dB with respect to the peak (unity) transmission of the Fabry-Pérot resonator. Taking these experimental challenges into account results in a Fabry-Pérot resonator design where the length, the mode number, and the coupler quality factor Q_c of the resonator are optimized. Furthermore multiple resonators on a single chip are used, each coupled to a separate antenna and detector, with different Q_c values. This design method is applicable for different dielectric materials and different transmission line configurations. Using this method a chip was designed and fabricated for a microstrip line based Fabry-Pérot resonator fabricated from sputter deposited superconducting NbTiN metal and a PECVD deposited a-Si layer. Using this chip a tanδ ≈ 10^-4 @ 350 GHz was measured, which represents the lowest loss values of a microstrip line at frequencies > 10 GHz ever measured. ... Read more

In this thesis, the implementation of a passive, chipless, frequency coded Radio-Frequency Identification (RFID) tag for bedload transport studies is proposed. The proposed tag will be deployed in the semi-arid Río Colorado river, Bolivia with the aim to develop quantitative sediment transport models that relate transport to grain size. The designed tag is an open-loop resonator with a fragment-loading structure, that has an op- timised configuration based on a Multiobjective Evolutionary Algorithm based on Decomposition combined with Enhanced Genetic Operators (MOEA/D-GO). The designed RFID tag can ideally reach a size of 4 by 4 millimetres with a maximum calculated reading range of 1.3 meters, and operates in the ultra wide band from 3 to 7 gigahertz. Numerous simulations on the tags were run to verify their properties. The tags proved to have a good directivity, quality factor and radio cross section on its resonant frequency. The tags could reach resonance frequencies as low as 2.9 gigahertz and quality factors as high as 130. The proof of concept on a Printed Circuit Board with an FR-4 substrate results in a tag of 6.4 by 3.4 millimetres. Unfortunately, these properties could not yet be verified by measuremen ... Read more

Spatial cues allow a listener to determine the direction sound is coming from. In addition, recognising spatially separated sound sources facilitate the listener to focus on specific sound sources. Because of this, preservation of spatial cues in multi-microphone hearing assistive devices is important to the listening experience and safety of the user.
A number of linearly-constrained-minimum-variance-based methods exist for this purpose. Most of these are limited in the number of interfering sources for which they can preserve the spatial cues. In this thesis, a method of selecting the most important interfering point sources using convex optimisation is proposed.
The method is presented based on two different convex relaxations, which are compared, using simulation experiments, to existing, exhaustive search and randomised methods in terms of noise suppression and localisation errors.
Both methods are shown to improve the performance of the joint binaural linearly constrained minimum variance beamformer, an existing method for simultaneous noise reduction and spatial cue preservation, by giving it more degrees of freedom for noise reduction and allowing it to handle a larger number of (virtual) sources present in the scene. ... Read more

In this thesis, a we have designed and fabricated a Josephson Parametric Amplifier (JPA) using a new double-angle evaporation method without a Dolan bridge. We have found and resolved several issues in the fabrication procedure, but it requires further tuning before being fully functional. We have also simulated the behaviour of a general parametric amplifier with an additional Duffing non-linear term, and found that this term appears to limit the oscillation amplitude. We have attempted to characterize Josephson junctions fabricated with the new double-angle evaporation procedure, but without much success. Using a different fabrication method, a JPA was made and successfully characterized. The maximum measured gain is 16 dB, with a bandwidth of 1 MHz. The noise temperature is comparable to the cryostat temperature of 250 mK, but it was not characterized accurately. ... Read more

DESHIMA is a superconducting on-chip spectrometer using MKIDs in the sub-mm wavelength regime (240-720 GHz, 1:3 bandwidth). This thesis presents (1) an analysis of the quasi-optical system used for DESHIMA on the ASTE telescope in Chile (2) design of the room-temperature optics of this design and (3) a preliminary investigation into an ultra-wideband leaky-lens antenna suitable for multi-pixel, constant aperture efficiency operation to be used as a feed to high f-number (>2) reflectors. The designed and analyzed optics show good performance and tolerance for the fall 2017 campaign of DESHIMA-on-ASTE. The wideband investigation leads to constant, >70% optical efficiency over the 1:3 bandwidth for a single pixel design (f-num=3.7) or >55% optical efficiency with multiple pixels spaced at 2*\lambda*f-number (f-num=5). Future work must be done to optimize the radiation efficiency of the antenna over the whole bandwidth, which is now the largest obstacle to frequency-dispersion free aperture efficiency. ... Read more