Precipitatieverschijnselen en spanningseffecten in geavanceerde aluminiumlegeringen

Chemical EngineeringApplied Science

Core-Shell Leaky-Wave Lens Antenna for 150GHz Fly’s Eye Communication Systems

This work presents a novel lens antenna architecture based on a core-shell lens design with a leaky-wave in-packaged antenna at 150GHz. An electrically small core lens made of dense dielectric material is used to enhance the radiation of the in-packaged antenna. A low-loss dielectric shell lens with electrically large dimensions is then added to provide high directivity. A microstrip feeding network for connection to a 150GHz chipset is then also discussed. The proposed lens antenna provides good quality patterns with aperture efficiencies above 80% over a bandwidth of 20%.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz SensingElectronic

Rapidly solidified (melt-spun) aluminium alloys: Morphology, texture and excess vacancies

AbstractChemical EngineeringApplied Science

A Wideband Leaky-Wave Lens Antenna with Annular Corrugations in the Ground Plane

We present a resonant leaky-wave lens antenna, fed by a circular waveguide with annular corrugations in the ground plane. The proposed leaky-wave feed reduces the impact of the spurious TM0 leaky-wave mode in all planes over a wide bandwidth while reducing assembly complexity compared to previous methods. The proposed leaky-wave antenna has an aperture efficiency above 80%, a return loss below -15 dB, and a cross-polarization level below -20 dB over a bandwidth from 110-220 GHz (2:1). We have fabricated and measured a WR-5 band (140-220 GHz) antenna prototype with a lens diameter of 3 cm that achieves excellent agreement between measurement and simulation in terms of return loss, directivity, and gain.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

High Aperture Efficiency Plastic Lens Antenna for Scanning Lens Phased Array at 180 GHz

In this contribution, we present a plastic resonant leaky-wave lens antenna with high aperture efficiency (>80%) over a 1:2 bandwidth centered at 180 GHz. This antenna can be integrated in a scanning lens phased array architecture for next-generation wireless and sensing applications that require high-directivity steerable beams. The high aperture efficiency is achieved thanks to the combination of annular corrugations in the ground plane with a leaky-wave resonant cavity. A WR-5 (140-220 GHz) prototype is manufactured and measured in terms of reflection coefficient, radiation patterns, directivity, losses, cross-polarization and scan performance, showing excellent agreement with simulations.Accepted author manuscriptTera-Hertz Sensin

First Demonstration of Dynamic High-Gain Beam Steering With a Scanning Lens Phased Array

We report on the first demonstration of dynamic beam steering using a scanning lens phased array. A scanning lens phased array relies on a combination of mechanical and electrical phase shifting to dynamically steer a high-gain beam beyond the grating-lobe free region using a sparse array. These two concepts have been demonstrated separately in the past, here we present, for the first time, a prototype demonstration where active mechanical and electrical phase shifting are combined. For this purpose, we have developed a sparse 4x1 scanning lens phased array at W-band (75-110 GHz) capable of beam steering a directive beam (>30 dBi) towards ± 20° with low grating lobe levels (around -10 dB). The lens array is fed by a waveguide-based leaky-wave feeding architecture that illuminates the lenses with high aperture efficiency over a wide bandwidth, which is required in the proposed scanning lens phased array architecture. The electrical phase shifting has been implemented using IQ-mixers around 15 GHz in combination with x6 multipliers to reach the W-band. The mechanical phase shifting relies on a piezo-electric motor, which is able to achieve displacements of the lens array of 6 mm with an accuracy of a few nanometers. The entire active array is calibrated over the air with an ad-hoc quasi-optical measurement setup. Resulting measurements show excellent agreement with the anticipated performance.Tera-Hertz SensingElectronic

Identification and classification of very low frequency waves on a coral reef flat

Very low frequency (VLF, 0.001–0.005 Hz) waves are important drivers of flooding of low-lying coral reef-islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a 5 month data set of water levels and waves collected along a cross-reef transect on Roi-Namur Island in the Republic of the Marshall Islands, the observed VLF motions were categorized into four different classes: (1) resonant, (2) (nonresonant) standing, (3) progressive-growing, and (4) progressive-dissipative waves. Each VLF class is set by the reef flat water depth and, in the case of resonance, the incident-band offshore wave period. Using an improved method to identify VLF wave resonance, we find that VLF wave resonance caused prolonged (∼0.5–6.0 h), large-amplitude water surface oscillations at the inner reef flat ranging in wave height from 0.14 to 0.83 m. It was induced by relatively long-period, grouped, incident-band waves, and occurred under both storm and nonstorm conditions. Moreover, observed resonant VLF waves had nonlinear, bore-like wave shapes, which likely have a larger impact on the shoreline than regular, sinusoidal waveforms. As an alternative technique to the commonly used Fast Fourier Transformation, we propose the Hilbert-Huang Transformation that is more computationally expensive but can capture the wave shape more accurately. This research demonstrates that understanding VLF waves on reef flats is important for evaluating coastal flooding hazardsEnvironmental Fluid Mechanic

Electrically Small High Permittivity Lens Antenna Using Artificially Loaded Thermoplastics at 170 GHz

This contribution presents the development of an electrically small lens antenna using an artificially loaded thermoplastic at 140-170GHz. We will present the on-going development of the Fly’s Eye front end antenna concept that was presented in [1]. The antenna is composed on a dual plastic lens, a core lens and a shell lens, fed by a double slot. The core-lens, being presented in this contribution, is a spherical lens made from an artificially loaded plastic of permittivity 9.5. To the best of our knowledge, this thermoplastic material has not been used for lens antennas in this frequency range before. A 4mm lens prototype has been developed using this material, which includes an antireflective layer synthesized by drilling sub-wavelength holes on the lens contour. Full-wave simulations show a negligible degradation of the performance of the anti-reflection layer compared to an ideal homogeneous matching layer. Physical measurements and antenna measurements confirm that the antenna's performance matches the design specifications.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz SensingElectronic

Al-Si Alloys Rapidly Quenched from the Melt

Chemical EngineeringApplied Science

Potential associations between immune signaling genes, deactivated microglia, and oligodendrocytes and cortical gray matter loss in patients with long-term remitted Cushing's disease

Introduction: Cushing's disease (CD) is a rare and severe endocrine disease characterized by hypercortisolemia. Previous studies have found structural brain alterations in remitted CD patients compared to healthy controls, specifically in the anterior cingulate cortex (ACC). However, potential mechanisms through which these persistent alterations may have occurred are currently unknown. Methods: Structural 3T MRI's from 25 remitted CD patients were linked with gene expression data from neurotypical donors, derived from the Allen Human Brain Atlas. Differences in gene expression between the ACC and an unaffected control cortical region were examined, followed by a Gene Ontology (GO) enrichment analysis. A cell type enrichment analysis was conducted on the differentially expressed genes, and a disease association enrichment analysis was conducted to determine possible associations between differentially expressed genes and specific diseases. Subsequently, cortisol sensitivity of these genes in existing datasets was examined. Results: The gene expression analysis identified 300 differentially expressed genes in the ACC compared to the cortical control region. GO analyses found underexpressed genes to represent immune function. The cell type specificity analysis indicated that underexpressed genes were enriched for deactivated microglia and oligodendrocytes. Neither significant associations with diseases, nor evidence of cortisol sensitivity with the differentially expressed genes were found. Discussion: Underexpressed genes in the ACC, the area vulnerable to permanent changes in remitted CD patients, were often associated with immune functioning. The specific lack of deactivated microglia and oligodendrocytes implicates protective effects of these cell types against the long-term effects of cortisol overexposure.Pattern Recognition and Bioinformatic