Silicon carbide formation in reactive silicon-carbon multilayers. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 44-48
An alternative low thermal budget silicon carbide syntheses route is presented. The method is based on self-propagating high-temperature synthesis of binary silicon-carbon-based reactive multilayers. With this technique, it is possible to obtain cubic polycrystalline silicon carbide at relatively low annealing temperatures by a solid state reaction. The reaction starts above 600 ˚C. The transformation process proceeds in a four-step process. The reaction enthalpy was determined to be (-70 ± 4) kJ/mol.
https://doi.org/10.4028/p-7u1v90
Silicon carbide - graphene nano-gratings on 4H and 6H semi-insulating SiC. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 170-174
A technical methodology of fabrication of hierarchically scaled multitude graphene nanogratings with varying pitches ranging from the micrometer down to sub 40 nm scale combined with sub 10 nm step heights on 4H and 6H semi-insulating SiC for length scale measurements is proposed. The nanogratings were fabricated using electron-beam lithography combined with dry etching of graphene, incorporating a standard semiconductor processing technology. A scientific evaluation of critical dimension, etching step heights, and surface characterization of graphene nanograting on both polytypes were compared and evaluated.
https://doi.org/10.4028/p-wn4zya
Descending staircase detection for service robots based on M-sequence UWB radar. - In: 2021 18th European Radar Conference, (2022), S. 29-32
Service robotics is expected to be one of the central growth industries of this century. The technological key to this lies in the sufficient perception of the environment, even under difficult conditions, because mobile robots have to orientate themselves and navigate without collision under all circumstances. However, the safe detection of especially descending stairs is a big challenge so far. In this paper, the results of descending staircase detection using UWB radar are shown. The individual steps of the signal processing from signal preparation to multi-target tracking are briefly explained and an outlook is given on how to classify a staircase based on the results. For all investigated stairs the edge of the first step could be detected reliably from a distance of 1.5 m and multiple steps are distinguishable as well.
https://doi.org/10.23919/EuRAD50154.2022.9784493
Angle-dependent reflectivity of microwave absorbers at oblique wave incidence. - In: 2021 51st European Microwave Conference, (2022), S. 233-236
For frequencies in the GHz-range, anechoic chambers are usually evaluated using ray-tracing techniques to locate disturbing reflections off the chamber walls. Most approaches reduce this wave-absorber interaction to a specular reflection, although the absorbers may extend over several wavelengths in size and display a rough surface. In order to develop more realistic ray-tracing models, the reflection characteristics of absorbers must be evaluated based on physical wave phenomena. In this paper, a measurement method is proposed which extends the established NRL-arch to measure the angle-dependent reflectivity for non-specular cases. First measurement results of commercial pyramidal absorbers in the frequency range between 1GHz and 10GHz indicate that the assumption of specular reflections is not justified, as power is reflected over a wide angular range with approximately the same intensity. This effect is, to our knowledge, currently not implemented in ray-tracing methods. These results contribute to a better understanding of the properties of RF absorbers to improve the efficiency of their use.
https://doi.org/10.23919/EuMC50147.2022.9784282
Localization and navigation of service robots by means of M-sequence UWB radars. - In: 2021 18th European Radar Conference, (2022), S. 189-192
The use of service robots has become much more relevant in industry and retail in recent years. To be of best possible benefit to humans, an autonomous motion ability of the service robots is of central importance. This requires that the robot can perceive its surroundings as precisely as possible by using different sensors and their fusion. In contrast to optical sensors, an UWB sensor can, for example, detect small and almost invisible objects such as glass panes with high range resolution. In this paper, a signal processing chain for detection of the environment with M-sequence UWB sensors is proposed. The proposed chain includes pulse reconstruction based on calibration measurements, background subtraction, object detection based on CFAR techniques, and multi-target tracking based on the Kalman filter and the nearest-neighbor approach.
https://doi.org/10.23919/EuRAD50154.2022.9784511
Impact of small-cell deployment on combined uplink and downlink RF exposure compared to the status quo in mobile networks. - In: 2021 51st European Microwave Conference, (2022), S. 618-621
As new cellular technologies are introduced in mobile networks nowadays, more and more small cells and mobile road side units are being deployed to upgrade the performance of the wireless communication network. With regard to the overall human RF exposure, the question arises to what extent the exposure is affected by the deployment of such small cells compared to macro cells as the status quo. In an attempt to answer this important question, this paper proposes a method to measure and evaluate the combined uplink and downlink exposure in terms of the specific absorption rate of a mobile phone user at recently installed small cell locations. The comparison between the small cell and macro cell scenarios revealed a reduction of the total exposure when the user equipment was logged into the investigated LTE small cells, although the downlink exposure increased. The main reason for this encouraging result is the reduction of the uplink transmission power due to the improved link conditions across the small cell. In contrast, the total exposure in a macro cell scenario is dominated by the uplink exposure. In order to minimise the total exposure, a balance must be sought between downlink and uplink exposure.
https://doi.org/10.23919/EuMC50147.2022.9784284
Broadband Ku- and Ka-band circulators in LTCC using sintered bulk ferrites. - In: 2021 51st European Microwave Conference, (2022), S. 18-21
This paper presents a novel approach of designing and fabricating compact microstrip circulators in low-temperature co-fired ceramics (LTCC) for Ku- and Ka-band satellite communications. State-of-the-art soft ferrites are embedded into LTCC boards as sintered bulk ceramics by using an advanced co-firing technology. The combination of (1) precise machining of the ferrites and low tolerance shrinking and (2) careful EM modelling by taking into account technological constraints, leads to reproducible fabrication and good circulator characteristics. We report simulation and measurement results in good agreement for broadband designs in Ku- and Ka-band.
https://doi.org/10.23919/EuMC50147.2022.9784350
A data-driven approach for stochastic modeling of automotive radar detections for extended objects. - In: Ulm 2022 GeMiC, (2022), S. 80-83
Radar sensors play an important role in automated driving technologies. However, the rising number of sensors deployed to enable autonomous driving functions leads to enormous validation efforts. While simulations are a possible approach to accelerate the validation process, the development effort for realistic sensor models increases significantly. Data-driven sensor models offer the possibility to replicate sensor data accurately and efficiently. Using real measurement data, the sensor output can be simulated without the detailed parametric modeling of the wave propagation and sensor effects. In this paper, the radar signatures of a passenger vehicle under a constant aspect angle are analyzed in real measurements. Then, a data-driven approach for stochastically modeling the radar target detections is presented. The model is trained with real sensor data to achieve a high degree of realism. A qualitative comparison between the simulated and measured detections reveals promising results.
https://ieeexplore.ieee.org/document/9783497
Kalibriereinrichtung für Wärmestromsensoren. - In: Sensoren und Messsysteme, (2022), S. 482-486
Vorstellung des Konzepts eines keramischen Wärmestromsensors. - In: Sensoren und Messsysteme, (2022), S. 336-340