Zeitschriftenaufsätze

Currently, 5G low-earth orbit satellite communications offer enhanced wireless coverage beyond the reach of 5G terrestrial networks, with important implications, particularly for automated and connected vehicles. Such wireless automotive mass-market applications demand well-designed compact user equipment antenna terminals offering non-terrestrial jointly with terrestrial communications. The antenna should be low-profile, conformal, and meet specific parameter values for gain and operational frequency bandwidth, tailored to the intended applications, in line with the aesthetic design requirements of passenger cars. This work presents an original concept for a dual-band nested circularly polarized automotive user terminal that operates at the S-band frequencies around 3.5 GHz and Ka-band frequencies around 28 GHz, namely within the 5G new-radio bands n78 and n257, respectively. The proposed terminal is designed to be integrated into the plastic components of a passenger vehicle. The arrays consist of 2 × 2 aperture-coupled corner-truncated microstrip slot patch antenna elements for the n78 band and of 4 × 4 single-layer edge-truncated microstrip circular slot patch antenna elements for the n257 band. The embedded arrays offer, across the two bands, respectively, 9.9 and 13.7 dBi measured realized gain and 3-dB axial ratio bandwidths of 100 and 1500 MHz for the n78 and n257 bands along the broadside direction. Detailed link budget calculations anticipate uplink data rates of 21 and 6 Mbit/s, respectively, deeming it suitable for various automotive mobility and Internet-of-Things applications.

The increasing demand for micro- and nanofabrication and in parallel the increasing requirements on feature size and resolution is leading to an enormous growth in the field of multi-photon three-dimensional fabrication. To enable new and diverse investigations in this field and to enable high precision for nanofabrication on large areas, a high precision positioning system is combined with an ultra-short pulse laser system. The aim is a modular setup with constant adherence to the Abbe-comparator principle in order to achieve systematic improvements in the area of Direct Laser Writing. For a high-quality identification of the microstructures a measurement tool based on atomic force microscopy is used. To enable the fabrication of continuous micro- and nanostructures on large area, an extremely high positioning precision is used, where no further stitching methods are necessary. Therefore as base of the Direct Laser Writing system the nanopositioning and nanomeasuring machine (NMM-1) is used, which was developed at Technische Universität Ilmenau together with SIOS Meßtechnik GmbH, with a positioning volume of 25 mm × 25 mm × 5 mm and a positioning resolution in the sub-nanometer range. First investigations already confirmed that microfabrication with a Femtosecond Laser and the NMM-1 could be realized and showed the possibility of further developments in the field of Direct Laser Writing. Now the modular structure as a research platform is designed in such a way that the various extensions and measurement setups for large-scale investigations can always be implemented in a metrologically traceable manner. The presented work shows the development of a modular functional setup of an exposure system and NMM-1, which enables micro- and nanofabrication and an improvement in the structure size over large areas.

Bobbin tool friction stir welding (BTFSW) is a variant of the FSW process which uses the special two-shoulder tool that forms the top and bottom of a weld surface. As such, a significant simplification of the welding setup is achieved. One of the dominant parameters of the BTFSW process is the interference between the tool shoulder pinch gap and the weld metal thickness. In this research, the influence of interference of the square pin tool with convex shoulders on process temperature, microstructure, tensile, impact, and bend performance were studied, and appropriate correlations were devised. The base metal was an aluminum-magnesium alloy in which the interference varied in the range of 0.1 to 0.5 mm. Wormhole defects and irregularities were found in all specimens except in the specimen welded with 0.4 mm interference. An optimal interference of 0.4 mm resulted in the best mechanical properties, which, in terms of tensile strength and reduction of area, were similar to the base metal. Furthermore, the impact strength was significantly higher, which was attributed to the grain refinement effect in the nugget zone.

Electrochemical reduction of CO2 to valuable products, powered by renewable energy, provides a promising strategy for reducing our dependence on fossil fuels. But up to now, no technology has been implemented for large-scale industrial applications. Without massive utilization of CO2, many vital practical problems, such as reducing CO2 emissions, storing renewable energy, and alleviating environmental pollution, cannot be resolved through this route. Herein, we propose a novel electrolyzer for CO2 electro-reduction, which is separated into three chambers by a bipolar membrane and a cation exchange membrane. In the cathodic chamber, CO2 is reduced to CO in organic electrolytes. In the anodic chamber, Cl- is oxidized to Cl2 in NaCl aqueous solution. In the central chamber, NaOH is obtained. The generated CO and Cl2 can be used as feedstock to produce phosgene (CO+Cl2 =COCl2). Through this route, phosgene can be produced from CO2 and NaCl, with NaOH generated as a byproduct. By substantially increasing the product value, we can promote CO2 electro-reduction technology to industrial applications.

The extension of low-earth orbit (LEO) services to non-terrestrial mobile communications has huge potential for eliminating network white spots and providing high-speed, low-latency links with worldwide geographic coverage. State-of-the-art user terminals for mobile platforms are too large for integration into a passenger vehicle. Antenna elements loaded with a dielectric superstrate could potentially lead to a considerable miniaturization of the user terminal. As per link budget calculations, an array with a gain of 27 dBi is necessary to ensure a throughput of 25 Mbps in the downlink at the Ku-band. A conventional array with a gain of 6 dBi per element, assuming a 12 × 12 arrangement with half-wavelength spacing, would require a footprint of 36 λ2 at 10 GHz to achieve this target and appears unsuitable for automotive integration. This paper proposes a low-profile, dual-band, dual-polarized, vertically stacked patch antenna with superstrate loading and shows that the inclusion of the superstrate improves the antenna’s gain by at least 3 dB. Therefore, compared to a conventional array, a superstrate-loaded array would need only half of the number of elements to meet the target gain, thus occupying only half of the surface area, and offers better integration for automotive applications. Requiring half of the number of elements also implies considerably reduced design complexity and cost.