Analytical and experimental studies of ground reflections on bi-static radar signal propagation. - In: AMTA 2022 proceedings, (2022), insges. 6 S.
Progressing towards highly automated and connected vehicles, radar systems have evolved into reliable assistance systems for environmental perception, for a wide spectrum of traffic scenarios, and with them, accurate angle-dependent descriptions of reflectivities and scattering centers of traffic participants and road users. Depending on the electrical size of the radar object, the influence of possibly unwanted ground reflections can be significant in radar cross-section measurements. This paper presents an analytical model based on the transmitter, receiver, and single or multiple scattering center positions, that takes into account the geometric reflections at the ground floor and calculates the resulting interference. Considering also the bi-static crosstalk between the transmit and receive antennas, six different propagation paths are obtained, which differ in path delay and attenuation. Subsequent validation measurements in a semi-anechoic automotive antenna test facility confirm the analytical approach very well. Existing discrepancies between the single scattering center model and the measurements with a metal sphere could be corrected by a closer look at the position of the scattering center. Final measurements on realistic bicyclist dummies show that the model is also reliably applicable to extended radar targets.
https://doi.org/10.23919/AMTA55213.2022.9954954
Evaluation of the effect of local gas flows on keyhole geometry by means of a half-section setup. - In: 12th CIRP Conference on Photonic Technologies, (2022), S. 385-390
Increasing beam power of solid-state lasers enables high welding speeds for laser welding processes. However, increasing welding speeds lead to imperfections, especially spatter formation while processing high-alloy steels. A recent and novel approach to reduce the spatter formation is the utilization of a local gas flow to manipulate the keyhole pressure balance beneficially. To get a better understanding of the effect of the gas flow on the keyhole and its geometry during deep penetration welding, a half-section setup was developed. The laser beam was positioned partially on a glass plate and the metal sheet to provide an insight into the processing zone by means of high-speed recordings. Thus, it was possible to measure the keyhole geometry and to quantify the effect of different welding speeds and gas flows on keyhole length for full penetration welds.
https://doi.org/10.1016/j.procir.2022.08.172
Characterization of keyhole dynamics in laser welding of copper by means of high-speed synchrotron X-ray imaging. - In: 12th CIRP Conference on Photonic Technologies, (2022), S. 501-506
Laser welding of copper is of great importance for industrial applications, e.g., for manufacturing of electrical components such as hairpins. Solid state lasers are widely used due to the high power and beam brilliance, but the implementation can be challenging in terms of process instabilities and resulting weld defects, i.e., spatter and pore formation. In order to understand the formation thus avoid these defects, the development of the understanding of the keyhole and its interaction with the surrounding melt pool is required. In this paper, high-speed synchrotron X-ray imaging (frame rate: 20,000 Hz) demonstrated its capability to study the keyhole geometry to quantify and describe the dynamic behavior inside the workpiece. Thus, novel insights into fundamental processes are provided and a new methodic approach was introduced to describe the time-dependent behavior of the keyhole and its interaction with the melt pool during laser beam deep welding of copper (Cu-ETP/CW004A).
https://doi.org/10.1016/j.procir.2022.08.079
Deep learning aided interpolation of spatio-temporal nonstationary data. - In: 30th European Signal Processing Conference (EUSIPCO 2022), (2022), S. 2221-2225
Despite the growing interest in many fields, spatio-temporal (ST) interpolation remains challenging. Given ST nonstationary data distributed sparsely and irregularly over space, our objective is to obtain an equidistant representation of the region of interest (ROI). For this reason, an equidistant grid is defined within the ROI, where the available time series data are arranged, and the time series of the unobserved points are interpolated. Aiming to maintain the interpretability of the whole process while offering flexibility and fast execution, this work presents a ST interpolation frame-work which combines a statistical technique with deep learning. Our framework is generic and not confined to a specific application, which also provides the prediction confidence. To evaluate its validity, this framework is applied to ultrasound nondestructive testing (UT) data as an example. After the training with synthetic UT data sets, our framework is shown to yield accurate predictions when applied to measured UT data.
https://ieeexplore.ieee.org/document/9909600
Estimating multi-modal dense multipath components using auto-encoders. - In: 30th European Signal Processing Conference (EUSIPCO 2022), (2022), S. 1716-1720
We present a maximum-likelihood estimation algorithm for radio channel measurements exhibiting a mixture of independent Dense Multipath Components. The novelty of our approach is in the algorithms initialization using a deep learning architecture. Currently, available approaches can only deal with scenarios where a single mode is present. However, in measurements, two or more modes are often observed. This much more challenging multi-modal setting bears two important questions: How many modes are there, and how can we estimate those? To this end, we propose a Neural Net-architecture that can reliably estimate the number of modes present in the data and also provide an initial assessment of their shape. These predictions are used to initialize for gradient- and model-based optimization algorithm to further refine the estimates. We demonstrate numerically how the presented architecture performs on measurement data and analytically study its influence on the estimation of specular paths in a setting where the single-modal approach fails.
https://ieeexplore.ieee.org/document/9909796
Bio-inspired acoustic sensor with gain adaptation enhancing dynamic range and onset detection. - In: 2022 IEEE International Symposium on Circuits and Systems (ISCAS), (2022), S. 789-793
The exceptional capability of humans to perceive speech in varying acoustic environments could not yet be achieved by technological speech processing systems. Possible reasons for this might be that (i) signal pre-processing occurring in the inner ear before and during transduction is implemented in technological systems only after the transduction stage and (ii) adaptation of the transduction stage with incorporated pre-processing is not included. Here, we present a novel, nonlinear acoustic sensor system including adaptation. Thereby, (short-term) adaptation is implemented using automatic gain control by discrete analog circuits. Thus, the sensor includes pre-processing capabilities like frequency decomposition, nonlinear amplification of signals and adaptation of sensing properties to varying acoustic inputs. The integration of the adaptation mechanism into the sensor system not only enhances important sound features like sound onset but also increases its dynamic range by increasing sensitivity for low volume sounds and preventing saturation for large volume sounds. A flexible design with tuneable components allows adaptation on different time scales (short- and long-term adaptation).
https://doi.org/10.1109/ISCAS48785.2022.9937484
Effect of line structures on the self-propagating reaction of Al/Ni multilayer. - In: 2022 IEEE 9th Electronics System-Integration Technology Conference (ESTC), (2022), S. 379-382
This work investigates the influence of a structured chip surface on the propagation of a self-sustaining reaction that is aimed to be used as heat source for chip assembly. A silicon (100) surface was structured by a combination of thermal oxidation and dry and wet etching to obtain line structures with height lesser than 1 µm. To ensure reaction of 5 µm thick Al/Ni multilayers, 1 µm of SiO2 is used as thermal insulator. Different widths of lines and valleys, with a ratio of 1:1, were processed. Width values were chosen to be 30 µm, 50 µm and 80 µm. Bilayer thickness of 50 nm with a 50/50 at% of Al/Ni were deposited using magnetron sputtering. By using focused ion beam with integrated scanning electron microscope and X-ray diffractometer the samples were analyzed prior to reaction. Velocity and temperature were measured with high-speed camera and high-speed pyrometer. Variations in reaction speed depending on the structure width were recorded and analyzed in perspective of the influence of the additional inclined reaction path. Calculation of the extended reaction paths and their influence on the reaction speed between the structures was performed. The results show that the additional distance has only a low influence on the velocity. Different reasons were identified, but it was not possible to determine the main cause. It was possible to slow down the reaction and keeping the temperature over 350 ˚C for over 500 ms, which provides enough energy to melt solders. The influence of smaller structures can be applied to bonding applications with reactive multilayers.
https://doi.org/10.1109/ESTC55720.2022.9939472
Time-domain analysis of ultra-wideband scattering properties of fruits. - In: 2022 19th European Radar Conference, (2022), S. 77-80
In the present paper we evaluate scattering properties of fruits measured with a short-range Ultra-Wideband radar. This is part of our investigation how effectively such a radar can be used to infer information such as fruit biomass or ripeness in an agricultural environment. The covered frequency band spans from 1.4 to 5.6 GHz. We analyze measured impulse responses of a watermelon, a grapefruit, and an apple with respect to a dependency on the distance between radar and fruit and the observation angle i.e., rotation of the fruit. Measurements are performed under laboratory conditions, however, we analyze the data considering a pre-harvest analysis on a field. It becomes apparent that an analysis of the dispersed dominant reflection of the peel is most promising. Due to the natural growth and hence anisotropy of the fruits, we conclude to average over multiple monostatic observation angles to reduce the natural variations of e.g. the scattered power.
https://doi.org/10.23919/EuRAD54643.2022.9924720
Ceramic additive manufacturing for high-performance microwave circuits. - In: 2022 24th International Microwave and Radar Conference (MIKON), (2022), insges. 4 S.
The recent advances in the ceramic additive manufacturing allow to develop structures that were unobtainable before. This opens up possibilities for spatial design of antennas, filters, microwave circuits, sensors and microsystems. Simple structures had been already reported using top-level equipment. We have analyzed the possibility to obtain similar results using less expensive devices to make the technology more accessible and introduce it to the wider public. We found that the commercially-available materials have high porosity and thus high dielectric losses. Therefore, we have developed a proprietary composition which can be used with inexpensive 3D printers. It offers high density and dielectric properties very close to well-established materials. Moreover, it has lower sintering temperature than typical ceramic materials, which allows to embed conductive traces inside of the structure. This technology has a potential to expand capabilities of microwave devices, especially in high-performance space and biosensor applications. Furthermore, we have developed a method to directly print spatial transparent polymeric structures on ceramic substrates, which allows to integrate optical and microwave circuits in one device.
https://ieeexplore.ieee.org/document/9924862
Link budget and design approach of a non-terrestrial 5G automotive antenna. - In: 2022 52st European Microwave Conference, (2022), S. 864-867
5G low-earth orbiting satellites are continuously increasing attention from automotive industry for automated and connected driving. Compactness of user equipment antennas and high data rates are key performance figures for efficient satellite communication systems. Here, we present a link budget for internet-of-things applications at Ka-band frequencies (5G frequency range FR2). Anticipating a realistic high-gain satellite antenna, an uplink data rate of 4 Mbit/s can be achieved with a compact user terminal antenna with a moderate gain of 13 dBi. Along these lines, a 4×4 patch antenna array was designed for seamless embedding in the plastic part of a car body, in order to verify the link budget calculations by experiment. The radiation performance was measured under free-space conditions and with the antenna embedded in the rear spoiler wing of a modern passenger car. The array offered 11.2 dBi realized gain and 1.6 GHz of −10 dB matching bandwidth, with an uplink data rate of 2 Mbit/s, promising for many mobility applications.
https://doi.org/10.23919/EuMC54642.2022.9924379