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During the last years, much progress has been made in hierarchical planning towards domain-independent systems that come with sophisticated techniques to solve planning problems instead of relying on advice in the input model. Several of these novel methods have been integrated into the PANDA framework, which is a software system to reason about hierarchical planning tasks. Besides solvers for planning problems based on plan space search, progression search, and translation to propositional logic, it also includes techniques for related problems like plan repair, plan and goal recognition, or plan verification. These various techniques share a common infrastructure, like e.g. a standard input language or components for grounding and reachability analysis. This article gives an overview over the PANDA framework, introduces the basic techniques from a high level perspective, and surveys the literature describing the diverse components in detail., publishedVersion

Next-generation radar sensors require imaging capabilities with high angular resolution. As for a single sensor, the aperture, and thus the achievable resolution, is limited due to the constraints of the front end, radar networks consisting of multiple sensors are a possible solution. However, their incoherency usually makes joint angle estimation impossible. This article presents a network concept consisting of an orthogonal frequency-division multiplexing (OFDM) radar and repeater elements, which receive the reflections from targets and retransmit them back to the radar. Thereby, any frequency conversion from radio frequency to baseband and vice versa is omitted such that the signal remains coherent to the initial transmit signal. To distinguish the bistatic signal transmitted by the repeater from the monostatic one of the OFDM radar, the orthogonal subcarrier structure of OFDM waveforms is exploited by combining a sparse radar transmit signal with a low-frequency modulation in the repeater. This allows to evaluate the bistatic signals at the radar with standard multiple-input-multiple-output (MIMO)-OFDM signal processing, leading to separate range-Doppler images for each virtual channel. Finally, it is shown that this method offers a coherent angular estimation based on the extended aperture of the network. For this purpose, a method to establish phase coherency by a reconstruction of the modulation phase is presented. The network concept is proved with measurements at 77 GHz., publishedVersion

To strain or not to strain: We calculate the strain dependence of metal anode surface properties from first principles to explore whether surface stress can be related to dendrite growth in metal-ion batteries on the atomistic level. We only find a weak dependence of these properties on the applied strain, which suggests that strain does not influence dendrite growth on the atomistic scale, but rather dendrite-related morphologies on longer-length scales. Dendrite growth poses a significant problem in the design of modern batteries as it can lead to capacity loss and short-circuiting. Recently, it has been proposed that self-diffusion barriers might be used as a descriptor for the occurrence of dendrite growth in batteries. As surface strain effects can modify dendritic growth, we present first-principles DFT calculations of the dependence of metal self-diffusion barriers on applied surface strain for a number of metals that are used as charge carriers in batteries. Overall, we find a rather small strain dependence of the barriers. We mainly attribute this to cancellation effects in the strain dependence of the initial and the transition states in diffusion., publishedVersion

Distributed scenarios pose a big challenge to tracking and fusion systems. They require the prevention of repeatedly incorporating the same information, which originates from ring closures in the communication path and would affect optimality. Additionally, the multi-sensor multi-object Generalized Labeled Multi-Bernoulli filter update is NP-hard in principle. The method proposed in this paper tackles these problems, as it constitutes a divide and conquer strategy for distributed, synchronized multi-sensor systems with central fusion. Based on a common prediction, local sensor updates are calculated separately, sent back and fused centrally in order to start a new cycle. Thus, the intractable multi-sensor update is split into less complex local single-sensor updates and a novel, low-complexity fusion strategy. The proposed method enables a full parallelization of the optimal multi-sensor Generalized Labeled Multi-Bernoulli and δ -Generalized Labeled Multi-Bernoulli update. Our approach bases on the Bayes Parallel Combination Rule and can be seen as multi-sensor multi-object Information Matrix Fusion for synchronous sensors, which constitutes a perfect choice in centralized systems with distributed sensors. Finally, we compare the proposed method to the Iterator Corrector approach from literature in detailed simulations., acceptedVersion

Radar networks offer the opportunity of enhancing the radar sensing performance beyond the inherent limitations of single multiple-input multiple-output (MIMO) radars. Different locations of the individual sensor nodes allow for diverse observation angles on the targets. Moreover, in case of a coherent network, such as radar-repeater networks, the direction of arrival (DoA) capabilities are increased. However, a crucial point in exploiting the full potential of a sensor network is the separability of the signals originating from the different sensor nodes during operation, while preserving reasonable radar sensing performance of the individual sensors and the network. In this paper multiplexing methods for an orthogonal frequency-division multiplexing (OFDM)-based radar network are proposed and investigated. The first method combines traditional time and frequency multiplexing, while the second method applies a random assignment in combination with a compressed sensing-based signal evaluation. Both methods are compared with the traditional FDM multiplexing for MIMO-OFDM. For this purpose, performance criteria are proposed and the concepts are evaluated based on measurements and simulations., acceptedVersion

Materials science is highly significant in space program investigation, energy production and others. Therefore, designing, improving and predicting advanced material properties is a crucial necessity. The high temperature creep and corrosion resistance of Ni-based superalloys makes them important materials for turbine blades in aircraft engines and land-based power plants. The investment casting process of turbine blades is costly and time consuming, which makes process simulations a necessity. These simulations require fundamental models for the microstructure formation. In this paper, we present advanced analytical techniques in describing the microstructures obtained experimentally and analyzed on different sample’s cross-sectional images. The samples have been processed on board the International Space Station using the MSL-EML device based on electromagnetic levitation principles. We applied several aspects of fractal analysis and obtained important results regarding fractals and Hausdorff dimensions related to the surface and structural characteristics of CMSX-10 samples. Using scanning electron microscopy (SEM), Zeiss LEO 1550, we analyzed the microstructure of samples solidified in space and successfully performed the fractal reconstruction of the sample’s morphology. We extended the fractal analysis on the microscopic images based on samples solidified on earth and established new frontiers on the advanced structures prediction., publishedVersion

A hybrid thin film multilayer antenna for automotive radar is presented in this work. A 2×8 aperture coupled stacked patch antenna array is realized on a single layer printed circuit board (PCB) using a novel thin film based approach. Using a compact 180 ◦ phase difference power divider, inter-element spacing in a 2×2 sub-array is reduced. Measurement results show a 19% (67.9–82.5 GHz) impedance bandwidth and a wideband broadside radiation pattern, with a maximum gain of 15.4 dBi realized gain at 72 GHz. The presented antenna compares favorably with other multilayer PCB antennas in terms of performance, with the advantage of simpler manufacturing and robust design. The antenna can be employed in mid-range automotive radar applications., acceptedVersion

There is a growing demand for collaborative robots in order to improve the ef���ciency of industrial processes and to push Industry 4.0 forward. The challenge for these robots is the compliance of the safety regulations to protect human workers from injuries. Therefore, a large number of sensors for the close range (several centimeters up to some meters) around the robot are needed. For a protective cover around the robotic arms all sensors must cooperate and process their information together. This paper presents a close range proximity sensor based on a 160-GHz radar MMIC with a transition to two ���exible dielectric waveguides. On the low-loss waveguides, leaky-wave antennas with a large ���eld of view are distributed. This reduces the number of sensors and achieves a coverage area for one sensor of more than 2200 cm�� for a distance of 30 cm. For distances below 30 cm the sensor has blind areas. However, the expected extended targets like body parts can still be detected and the proximity sensor will stop the robot in the danger area. Additionally, the ���exible waveguide offers the possibility to place the antennas almost arbitrarily around the robotic arm. For a single target scenario it is even possible to determine the target position by multilateration with only one receive channel., publishedVersion

Modern consumer and industrial unmanned aerial vehicles (UAVs) are easy-to-use flying sensor platforms. They offer stable flight, good maneuverability, hovering, and even waypoint flights in autopilot mode. For stabilization and localization, sensors such as inertial measurement units (IMUs)-including gyroscopes and accelerometers-barometric sensors, and the Global Navigation Satellite System (GNSS) are used. To sense the UAV's direct environment, e.g., for collision avoidance or fully automated flight, additional sensors are needed. State-of-the-art combinations of infrared, ultrasonic, and vision-based sensors (monocular and/or stereo vision) capture the close vicinity. Using radar sensors is advantageous, as they are able to directly sense range and velocity and are not affected by lighting conditions and contrast. With the help of a multichannel radar, the angular information may also be extracted., acceptedVersion

Plasma electrolytic oxidation (PEO) is a novel surface treatment process to produce thick, dense metal oxide coatings, especially on light metals, primarily to improve their wear and corrosion resistance. The coating manufactured from the PEO process is relatively superior to normal anodic oxidation. It is widely employed in the fields of mechanical, petrochemical, and biomedical industries, to name a few. Several investigations have been carried out to study the coating performance developed through the PEO process in the past. This review attempts to summarize and explain some of the fundamental aspects of the PEO process, mechanism of coating formation, the processing conditions that impact the process, the main characteristics of the process, the microstructures evolved in the coating, the mechanical and tribological properties of the coating, and the influence of environmental conditions on the coating process. Recently, the PEO process has also been employed to produce nanocomposite coatings by incorporating nanoparticles in the electrolyte. This review also narrates some of the recent developments in the field of nanocomposite coatings with examples and their applications. Additionally, some of the applications of the PEO coatings have been demonstrated. Moreover, the significance of the PEO process, its current trends, and its scope of future work are highlighted., publishedVersion

In order to improve the resolution of imaging radars, electrically large arrays and high absolute bandwidths are required. At a large off-boresight angle of the incident wave, the difference in path length at the antennas becomes a multiple of the range resolution of the radar. Consequently, the radar responses of the targets at the different receiving channels are distributed over a large number of range bins, depending on the direction-of-arrival (DoA) of the target echo. Applying conventional signal processing, the resolution of the radar is considerably reduced. In this paper, the key aspects of DOA estimation are discussed when radars with both a large aperture size and a high absolute bandwidth are employed. A signal processing method is proposed avoiding errors that occur in conventional DOA estimation techniques. As shown by measurements, an angular resolution of 0.4�� can be achieved with an array size of 200 lambda and a bandwidth of 10GHz., acceptedVersion

Flawless operation even with a high density of radar sensors in the vicinity is an essential prerequisite for radar sensors in automotive applications, safety systems, future autonomous driving, and in industry applications. Recent research shows the great potential of digitally modulated radars such as orthogonal frequency-division multiplexing (OFDM). Furthermore, novel frequency agile OFDM approaches such as stepped and sparse OFDM are superior to standard OFDM as they are able to achieve high resolution beyond the hardware-related band limits. In order to prevent possible mutual interference issues of common and novel modulation schemes, the influence of a state-of-the-art FMCW on stepped and sparse OFDM is examined in this paper. The effects of interference are investigated theoretically and through measurements using an experimental OFDM setup at 76 GHz and scenarios with up to two FMCW interferers. To prevent signal deterioration and limited detection performance due to interference, an efficient but low-cost detection and mitigation approach is presented for each of the two approaches., acceptedVersion

For imaging radars, the calibration effort increases with higher frequency and finer angular resolution demands and is therefore one of the largest cost factors in radar production. In case of high angular resolution, the calibration is also sensitive to array misalignment, resulting in costly calibration procedures. This paper proposes an angle-dependent radar calibration method with significantly reduced calibration effort. The high efficiency and robustness against misalignment is achieved by exploiting phase symmetry of a target in the measured radar response. Based on an initial theoretical formulation followed by an experimental verification, this novel approach does not only yield a cost-effective calibration, but also increases the robustness against array misalignment., acceptedVersion

This paper presents the channel influence when simulating interference between automotive radars in realistic scenarios. As a starting point, a simple approach considering only the line-of-sight (LoS) component of the signal transmitted by the interferer radar is presented. Following, the influence of the ground reflections in interference situations is analyzed by introducing the two-path model. Properties of the road surface such as roughness and the Fresnel reflection coefficient are considered in order to obtain a more realistic simulation. A sweep of all the possible ranges between victim and interferer radars is performed, and the influence of the interferer radar is analyzed. Finally, a statistical analysis of the key radar parameters is carried out in order to evaluate the interference behavior in the presented model., acceptedVersion

A wastewater refinery is a multifunctional solution that combines different technologies and processing schemes to recover a spectrum of valuable materials from municipal or industrial wastewater. The concept of wastewater refinery introduces a new perspective on wastewater treatment and management. It aims at making the most of wastewater constituents by co-producing different worthful outputs, such as water, energy, nitrogen, sulfide, and phosphorous. This can turn the treatment of wastewater from a major cost into a source of profit. The wastewater refinery approach is well aligned with the concept of the circular economy. A case study on Qatar’s wastewater revealed the potential recovery of significant quantities of valuable resources embodied in the country’s wastewater. Valorization of organic constituents and the recovery of nitrogen, phosphorus, and sulfide should be given priority. To facilitate the adoption of the wastewater refinery concept, research is required to explore technical and economic bottlenecks., publishedVersion

Ionic liquids are promising candidates for novel electrolytes as they possess large electrochemical and thermodynamic stability and offer a high degree of tunability. As purely-ionic electrolyte without neutral solvent they exhibit characteristic structures near electrified interfaces and in the bulk, both being described theoretically via separate frameworks and methodologies. We present a holistic continuum theory applying to both regions. This transport theory for pure ionic liquids and ionic liquids-mixtures allows the systematic description of the electrolyte evolution. In particular, dynamic bulk-transport effects and interfacial structures can be studied. The theory is thermodynamically consistent and describes multi-component solutions (ionic liquids, highly concentrated electrolytes, water-in-salt electrolytes). Here, we give a detailed derivation of the theory and focus on bulk transport processes of ionic liquids as appearing in electrochemical cells. In addition, we validate our framework for a zinc-ion battery based on a mixture of ionic-liquid and water as electrolyte., publishedVersion

Automated vehicles need to not only perceive their environment, but also predict the possible future behavior of all detected traffic participants in order to safely navigate in complex scenarios and avoid critical situations, ranging from merging on highways to crossing urban intersections. Due to the availability of datasets with large numbers of recorded trajectories of traffic participants, deep learning based approaches can be used to model the behavior of road users. This paper proposes a convolutional network that operates on rasterized actor-centric images which encode the static and dynamic actor-environment. We predict multiple possible future trajectories for each traffic actor, which include position, velocity, acceleration, orientation, yaw rate and position uncertainty estimates. To make better use of the past movement of the actor, we propose to employ temporal convolutional networks (TCNs) and rely on uncertainties estimated from the previous object tracking stage. We evaluate our approach on the public "Argoverse Motion Forecasting" dataset, on which it won the first prize at the Argoverse Motion Forecasting Challenge, as presented on the NeurIPS 2019 workshop on "Machine Learning for Autonomous Driving"., acceptedVersion

Since the number of radar sensors per vehicle has been increasing in order to improve the performance of Advanced Driver Assistance Systems, mutual interference has become one of the most important challenges for near future automotive radar systems. Depending on the sensor parameters and the diverse properties of the traffic scenario, the interference effects can significantly vary. The effort to measure and appraise the interference in real traffic scenarios leads to the importance of designing a tool suited to simulate and analyze the interference. This paper presents a fast simulator capable of modeling, estimating, and evaluating the effects of interference in complex multi-user traffic scenarios. A statistical analysis of the interference in a proposed scenario is performed in order to validate the presented simulator., acceptedVersion

A variety of transitions from a monolithic microwave integrated circuit (MMIC) to a waveguide were proposed in literature to enable chip-to-chip links or to provide a standard interface. The MMIC is usually in contact with the waveguide and is therefore exposed to the mechanical stress exerted on the overall system. This paper presents mechanically decoupled transitions from MMIC to a rectangular waveguide and to a dielectric waveguide at G-Band (140 GHz to 220 GHz). Both transitions use a patch radiator on a quartz glass carrier as on-chip antenna. To focus the beam, a dielectric rod antenna or an elliptical dielectric lens is placed on the quartz glass. Since the transitions are mechanically decoupled, a second antenna is used as receive element. A horn antenna connected to the rectangular waveguide or a second dielectric lens connected to the dielectric waveguide is used. The transitions were characterized using a back end of line MMIC. The minimum measured insertion loss is 3.1 dB for the transition from MMIC to rectangular waveguide and 4.9 dB for the transition to dielectric waveguide., acceptedVersion

Monostatic,multiple-input-multiple-output (MIMO) radar configurations using the same antenna array for transmission and reception inherently lead to redundant virtual antenna positions within the virtual MIMO aperture. This article presents a new method for designing monostatic MIMO radars where this disadvantage may be overcome and nonredundant virtual arrays are yielded by exploiting biomimetic antenna arrays (BMAAs). The new concept of biomimetic MIMO is introduced and thoroughly investigated in this article. Its working principle is compared with conventional monostatic MIMO and verified by radar measurements. The new approach is intended to improve the angle estimation capability of, in particular, small radar systems. Therefore, the concept is applied to an ultracompact two-channel radar monolithic microwave integrated circuit (MMIC) with fully integrated antennas for range and angle measurements in the 150-GHz range. The chip features two monostatic transmit-receive (TRX) channels with an antenna spacing of ��/4 and occupies less than 3 mm�� of space. By applying biomimetic MIMO, a virtual aperture consisting of four unique antenna positions and an equivalent total size of around 1.5�� is achieved., publishedVersion

Biomimetic antenna arrays (BMAAs) are used to improve the angle estimation capabilities of compact antenna systems by mimicking the hearing system of an insect. The key component of the antenna system is the biomimetic coupling network. Recent works propose the use of transformers for this purpose, but these are difficult to realize especially in the mm-wave range. In this paper, a new topology for the biomimetic coupling network based on rat-race couplers is proposed and a straightforward design process is given. A prototype antenna is designed, fabricated, and measured showing an excellent match between theory and measurement., acceptedVersion

In this paper, we present a multimodal dataset for affective computing research acquired in a human-computer interaction (HCI) setting. An experimental mobile and interactive scenario was designed and implemented based on a gamified generic paradigm for the induction of dialog-based HCI relevant emotional and cognitive load states. It consists of six experimental sequences, inducing Interest, Overload, Normal, Easy, Underload, and Frustration. Each sequence is followed by subjective feedbacks to validate the induction, a respiration baseline to level off the physiological reactions, and a summary of results. Further, prior to the experiment, three questionnaires related to emotion regulation (ERQ), emotional control (TEIQue-SF), and personality traits (TIPI) were collected from each subject to evaluate the stability of the induction paradigm. Based on this HCI scenario, the University of Ulm Multimodal Affective Corpus (uulmMAC), consisting of two homogenous samples of 60 participants and 100 recording sessions was generated. We recorded 16 sensor modalities including 4 &times, video, 3 &times, audio, and 7 &times, biophysiological, depth, and pose streams. Further, additional labels and annotations were also collected. After recording, all data were post-processed and checked for technical and signal quality, resulting in the final uulmMAC dataset of 57 subjects and 95 recording sessions. The evaluation of the reported subjective feedbacks shows significant differences between the sequences, well consistent with the induced states, and the analysis of the questionnaires shows stable results. In summary, our uulmMAC database is a valuable contribution for the field of affective computing and multimodal data analysis: Acquired in a mobile interactive scenario close to real HCI, it consists of a large number of subjects and allows transtemporal investigations. Validated via subjective feedbacks and checked for quality issues, it can be used for affective computing and machine learning applications.

Imaging radars are usually realized fully coherently. However, the distribution of one common radio frequency signal to all transmit and receive paths requires a high degree of hardware complexity. In order to reduce the hardware effort significantly, a novel phase synchronization method for incoherent and quasi-coherent frequency-modulated continuous-wave (FMCW) imaging radars with individual signal synthesis per channel is presented. The quasi-coherent setup uses one common oscillator for all frequency synthesizers. It is shown that in the case of the quasi-coherent system, only a phase difference between the calibration and the measurement has to be corrected to achieve coherence. In comparison, an incoherent system causes additional time, frequency, and FMCW ramp slope errors due to the different behavior of the oscillators. In order to achieve phase coherence and to correct the error sources, a calibration-based method using a defined signal path as part of the radar system is proposed. The imaging radar used for verification of the theory consists of individual single-channel radar monolithic microwave integrated circuits (MMICs) at 160 GHz; each MMIC fed by an individual frequency synthesizer. As shown by measurements, it is possible to achieve phase coherence for both system approaches and to perform angle estimation., publishedVersion

An essential prerequisite for radars in automotive applications, safety systems, future autonomous driving, and industry applications is the reliable operation even under difficult conditions such as interference from other radars. Recently, digital radar principles such as orthogonal frequency-division multiplexing (OFDM) gained increasing attention. In this letter, an interference-robust processing for OFDM radar signals using compressed sensing (CS) is presented, which is particularly suitable for random OFDM but also applicable to stepped and standard OFDM. It allows robust radar operation in presence of interfering signals that have a comparable low instantaneous bandwidth and high narrowband power. The method is validated experimentally using measurements of an OFDM radar setup at 76 GHz and a state-of-the-art FMCW radar as an interferer., acceptedVersion

There exists a plethora of claims about the advantages and disadvantages of model transformation languages compared to general-purpose programming languages. With this work, we aim to create an overview over these claims in the literature and systematize evidence thereof. For this purpose, we conducted a systematic literature review by following a systematic process for searching and selecting relevant publications and extracting data. We selected a total of 58 publications, categorized claims about model transformation languages into 14 separate groups and conceived a representation to track claims and evidence through the literature. From our results, we conclude that: (i) the current literature claims many advantages of model transformation languages but also points towards certain deficits and (ii) there is insufficient evidence for claimed advantages and disadvantages and (iii) there is a lack of research interest into the verification of claims., publishedVersion

A robust and wideband differential microstrip line-to-WR6-waveguide transition for mixed multilayer PCBs at D-band is presented. The PCB stack is composed of three standard RF core materials with standard thicknesses. Compared to other inline transitions above 90 GHz, which are designed for single substrates, it can be applied to mixed multilayer circuits. The tapered transition is only 8.0-mm wide and 2.5-mm long, has an insertion loss between 1.2 and 1.8 dB, and a return loss higher than 10 dB for 30-GHz bandwidth around the center frequency of 120 GHz., acceptedVersion

In this letter, the capabilities of an incoherent radar sensor network for robust Doppler-based gesture recognition are investigated, and a significant performance boost is demonstrated. A comprehensive dataset is recorded with an incoherent sensor network consisting of three time-synchronized 77GHz frequency-modulated continuous wave radars. Based on this dataset, we show that differential Doppler features obtained from the varying viewing angles result in a significant multistatic gain for classification, particularly for high intraclass variations and low Doppler frequencies. For the most complex dataset, cross-user validation accuracy of a convolutional neural network with optimized data fusion is improved by 7.4% to an overall value of 87.1%, which we regard to be high as gestures are not designed for distinguishability but reflect everyday control and communication signals., acceptedVersion

A novel concept for a holographic antenna-in-package (AiP) is presented enabling the seamless integration of high gain antennas at millimeter wave frequencies. The antenna is based on a holographic impedance approach stimulating a leaky wave mode at 150 GHz. Since the antenna structure is placed on top of the glass package, a large antenna aperture with high angular beam width and efficiency were achieved. The surface wave launcher (SWL) of the antenna connected to the integrated active circuitry is designed in a very compact fashion using a vertical through-glass-via (TGV) and solder balls. The performance of the proposed holographic antenna package has been investigated by an analytic model and full wave simulations. The measurement results of the antenna prototype on glass using anisotropic unit cells show excellent agreement to the simulated values. A maximum gain of 24.7 dBi, a sidelobe level of 15 dB, and a 3 dB-beam width of 4.7�� are achieved. The measured 3D-radiation pattern shows a highly directive pattern in all cuts., acceptedVersion

n recent years, the energy production sector has experienced a growing interest in new energy vectors enabling energy storage and, at the same time, intersectoral energy applications among users. Hydrogen is one of the most promising energy storage and carrier media featuring a very high gravimetric energy density, but a rather low volumetric energy density. To this regard, this study focuses on the use of aluminum as energy storage and carrier medium, offering high volumetric energy density (23.5 kWh L−1), ease to transport and stock (e.g., as ingots), and is neither toxic nor dangerous when stored. In addition, mature production and recycling technologies exist for aluminum. Herein, the performance of power systems driven by aluminum powder in terms of electrical efficiency (η(I)) and round-trip efficiency (RTE) is analyzed. Along with the additional advantages relating to high volumetric energy density, and safety and management aspects, the aluminum-based technology appears to outperform the power-to-power systems based on hydrogen and liquid fuels., publishedVersion

Large high-resolution displays (LHRDs) provide an enabling technology to achieve immersive, isometrically registered, virtual environments. It has been shown that LHRDs allow better size judgments, higher collaboration performance, and shorter task completion times. This paper presents novel insights into human size perception using large-scale floor displays, in particular in-depth evaluations of size judgment accuracy, precision, and task completion time. These investigations have been performed in the context of six, novel applications in the domain of automotive production planning. In our studies, we used a 54-sqm sized LED floor and a standard tablet visualizing relatively scaled and true to scale 2D content, which users had to estimate using different aids. The study involved 22 participants and three different conditions. Results indicate that true to scale floor visualizations reduce the mean absolute percentage error of spatial estimations. In all three conditions, we did not find the typical overestimation or underestimation of size judgments., publishedVersion

The system concept of a compact three-dimensional (3D) imaging radar in the millimeter-wave range around 150 GHz is presented. The multiple-input multiple-output (MIMO) radar system is composed of two identical two-channel radar monolithic microwave integrated circuits (MMICs) with on-chip antennas arranged perpendicular to each other. Typically, such arrangements suffer from angular ambiguities due to large antenna spacings that come along with the MMIC footprint and printed circuit board (PCB) routing constraints. The concept of biomimetic antenna arrays (BMAAs) is used to mitigate the problem of ambiguities. The influence of applying a spherical lens to the radar system is discussed in the paper, and radar measurements show the applicability of the proposed concept., acceptedVersion

In order to improve the resolution of imaging radars, electrically large arrays and a high absolute modulation bandwidth are needed. For radar systems with simultaneously high range resolution and very large aperture, the difference in path length at the receiving antennas is a multiple of the range resolution of the radar, in particular for off-boresight angles of the incident wave. Therefore, the radar response of a target measured at the different receiving antennas is distributed over a large number of range cells. This behavior depends on the unknown incident angle of the wave and is thus denoted as range-angle coupling. Furthermore, the far-field condition is no longer fulfilled in short-range applications. Applying conventional signal processing and radar calibration techniques leads to a significant reduction of the resolution capabilities of the array. In this article, the key aspects of radar imaging are discussed when radars with both a large aperture size and a high absolute bandwidth are employed in short-range applications. Based on an initial mathematical formulation of the physical effects, a correction method and an efficient signal processing chain are proposed, which compensate for errors that occur with conventional beamforming techniques. It is shown by measurements that with an appropriate error correction an improvement of the angular resolution up to a factor of 2.5 is achieved, resulting in an angular resolution below 0.4�� with an overall aperture size of nearly 200 \lambda., publishedVersion

Motivated by the potential of ionic liquids (ILs) to replace traditional aqueous electrolytes in Zn-air batteries, we investigated the effects arising from mutual interactions between O2 and Zn(TFSI)2 as well as the influence of H2O impurities in the oxygen reduction/oxygen evolution reaction (ORR/OER) and in Zn deposition/dissolution on a glassy carbon (GC) electrode in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide (BMP-TFSI) by differential electrochemical mass spectrometry. This allowed us to determine the number of electrons transferred per reduced/evolved O2 molecule. In O2 saturated neat BMP-TFSI the ORR and OER were found to be reversible, in Zn2+ containing IL Zn deposition/stripping proceeds reversibly as well. Simultaneous addition of O2 and Zn2+ suppresses Zn metal deposition, instead ZnO2 is formed in the ORR, which is reversible only after excursions to very negative potentials (−1.4 V). The addition of water leads to an enhancement of all processes described above, which is at least partly explained by a higher mobility of O2 and Zn2+ in the water containing electrolytes. Consequences for the operation of Zn-air batteries in these electrolytes are discussed., publishedVersion

Information-theoretic bounded rationality describes utility-optimizing decision-makers whose limited information-processing capabilities are formalized by information constraints. One of the consequences of bounded rationality is that resource-limited decision-makers can join together to solve decision-making problems that are beyond the capabilities of each individual. Here, we study an information-theoretic principle that drives division of labor and specialization when decision-makers with information constraints are joined together. We devise an on-line learning rule of this principle that learns a partitioning of the problem space such that it can be solved by specialized linear policies. We demonstrate the approach for decision-making problems whose complexity exceeds the capabilities of individual decision-makers, but can be solved by combining the decision-makers optimally. The strength of the model is that it is abstract and principled, yet has direct applications in classification, regression, reinforcement learning and adaptive control., acceptedVersion

Especially for short-range radar sensors, a protection of the electronics against environmental damage like heat or humidity as well as a robust antenna front end are essential. In order to separate the sensitive electronics and the robust antenna spatially, a system concept for a 300-GHz radar with mechanically ���exible front end is presented in this paper. The ���exible front end is realized with a low-loss dielectric waveguide (DWG) with losses of around 15 dB/m. It is bendable up to a radius of 1 cm. An elliptical lens (30.9 dBi) at the end is used to focus the beam. The front end is fed by a radar MMIC in a QFN-like package with an integrated silicon lens. The wide beam is focused by simply placing a multimodal DWG above package and lens. The intentionally caused interference of the individual modes then results in a ���eld maximum in the center, and the fundamental mode can be fed into the DWG., acceptedVersion

For highly integrated imaging systems above 100 GHz, the complexity and chip area increases signi���cantly with increasing number of channels. In addition, bulky dielectric lenses prevent applications in spatially restricted surroundings. The presented concept of an imaging monopulse radar with a mechanically ���exible front end reduces the required chip area and allows the antenna to be placed in any desired position apart from the sensitive electronics. The radar system is based on a two-channel 160 GHz microwave monolithic integrated circuit (MMIC) feeding a ���exible dielectric waveguide. Depending on the angle of the incidence signal, a sum mode (HE11 mode) and a difference mode (HE21 mode) are excited in the dielectric waveguide. MMIC and waveguide are connected by a self-aligning transition reducing the requirements for packaging accuracy. The required chip area of the transition is only 0.022���� with a spacing between the on-chip antennas of ��/4. The measured ambiguity-free region between ���18�� and 15�� is de���ned by the modi���ed elliptical lens antenna focusing in the E-plane only. A mechanical bending of the ���exible waveguide is possible down to a radius of at least 2 cm without affecting the angle estimation capability., acceptedVersion

Information and communication technology (ICT) is an enabler for establishing automated vehicles (AVs) in today’s traffic systems. By providing complementary and/or redundant information via radio communication to the AV’s perception by on-board sensors, higher levels of automated driving become more comfortable, safer, or even possible without interaction by the driver, especially in complex scenarios. Additionally, communication between vehicles and/or a central service can improve the efficiency of traffic flow. This paper presents a reference architecture for such an infrastructure-based support of AVs. The architecture combines innovative concepts and technologies from different technological fields like communication, IT environment and data flows, and cyber-security and privacy. Being the basis for the EU-funded project ICT4CART, exemplary implementations of this architecture will show its power for a variety of use cases on highways and in urban areas in test sites in Austria, Germany, and Italy, including cross-border interoperability., publishedVersion

By structural and analytical TEM and scanning electron microscopy experiments we show thatatomically-resolved structural characterization of oxidation-sensitive two-dimensional material isstrongly hindered when thefinal step of the preparation process, the transfer to the TEM grid, isperformed with a wet etching method involving bases or acids, interacting with the highlyreactive sample surface. Here we present an alternative polymer-assisted and mechanical-exfoliation-based sample preparation method and demonstrate it on selected oxidation-sensitivetransition metal phosphorus trisulfides and transition metal dichalcogenides. The analysis,obtained from the samples prepared with both of the methods clearly show that oxidation is theorigin of discrepancy, the oxidation during thefinal preparation step is strongly reduced onlywhen the new method is applied, and atomically-resolved structural characterization of thepristine structures is now possible., publishedVersion

We use a combination of microwave fields and free precession to drive the spin of a nitrogen-vacancy (NV) center in diamond on different trajectories on the Bloch sphere, and investigate the physical significance of the frame-dependent decomposition of the total phase into geometric and dynamic parts. The experiments are performed on a two-level subspace of the spin-1 ground state of the NV, where the Aharonov-Anandan geometric phase manifests itself as a global phase, and we use the third level of the NV ground state triplet to detect it. We show that while the geometric Aharonov-Anandan phase retains its connection to the solid angle swept out by the evolving spin, it is generally accompanied by a dynamic phase that suppresses the geometric dependence of the system dynamics. These results offer insights into the physical significance of frame-dependent geometric phases., Comment: 10 pages, 5 figures

Publisher's version (útgefin grein), Improved understanding of the fundamental processes leading to degradation of platinum nanoparticle electrocatalysts is essential to the continued advancement of their catalytic activity and stability. To this end, the oxidation of platinum nanoparticles is simulated using a ReaxFF reactive force field within a grand-canonical Monte Carlo scheme. 2–4 nm cuboctahedral particles serve as model systems, for which electrochemical potential-dependent phase diagrams are constructed from the thermodynamically most stable oxide structures, including solvation and thermochemical contributions. Calculations in this study suggest that surface oxide structures should become thermodynamically stable at voltages around 0.80–0.85 V versus standard hydrogen electrode, which corresponds to typical fuel cell operating conditions. The potential presence of a surface oxide during catalysis is usually not accounted for in theoretical studies of Pt electrocatalysts. Beyond 1.1 V, fragmentation of the catalyst particles into [Pt6O8]4− clusters is observed. Density functional theory calculations confirm that [Pt6O8]4− is indeed stable and hydrophilic. These results suggest that the formation of [Pt6O8]4− may play an important role in platinum catalyst degradation as well as the electromotoric transport of Pt2+/4+ ions in fuel cells., B.K. thanks the University of Iceland Research Fund for support through a PhD fellowship, Dr. Anna Garden for access to nanoparticle DFT structures, and Marcos Tacca for translation help of Spanish primary literature. Andrey Sinyavskiy is acknowledged for implementing the 2PT method. This work was supported by the German Federal Ministry of Education and Research through the BMBF-project ?GEP ? Grundlagen elektrochemischer Phasengrenzen? (Grant No. 13XP5023D), the Deutsche Forschungsgemeinschaft (DFG) through Grant No. SFB-1316 (collaborative research center), as well as through the Icelandic Research Fund under Grant No. 174582-052. Computational resources were provided by the state of Baden?W?rttemberg through bwHPC and the German Science Foundation (DFG) under Grant No. INST 40/467-1 FUGG. The Volkswagen Group, Wolfsburg, Germany is acknowledged for partial funding of this project.

A novel hermetically sealed RF packaging concept based on glass is presented. Using the laser induced deep etching (LIDE) technology enables the fabrication of glass vias without degrading the mechanical stability as micro-cracks are completely avoided. Furthermore, aspect ratios of up to 1:10 make this technology superior over conventional packaging solutions for the upper millimeter wave regime beyond 150 GHz. As an initial design demonstration, this paper shows a vertical RF-transition through the glass substrate using Through-Glass Vias (TGVs) with an aspect ratio larger than 1:6. The realized prototypes intended for highly efficient LO/VCO distribution within the glass package show excellent reproducibility with a maximum insertion loss of 0.4 dB up to 40 GHz. In addition, a very compact RF-interconnection from PCB to the glass package using solder balls is presented. The simulation of the RF-transition is in good agreement with the measured reflection and transition coefficient not exceeding ���15 dB and ���1.5 dB up to 35 GHz, respectively., acceptedVersion

This paper presents an approach to estimate the true direction of motion and the velocity of a target within a single measurement snapshot. This is achieved by using a single radar sensor in combination with an active repeater element that is operated as a displaced virtual sensor. Coherency between sensor and repeater tag is only obtained by signal processing; on a hardware level both operate incoherently. This setup provides the necessary multi-perspective view on the target at low effort and large freedom of placement. The results of simulations and measurements in the 77 GHz band with one radar sensor and two repeater elements are presented to validate the theory., acceptedVersion

Multiple-input-multiple-output (MIMO) radars show improved angular resolution compared to traditional phased-array radar systems. Exploiting the advantages of MIMO radars could thus significantly improve the performances of the next generation of automotive radar sensors. The placement and the characteristics of the antenna arrays affect the performance of the MIMO system. For such applications, different metrics like the ambiguity function of the antenna system must be accurately evaluated. This letter presents a detailed characterization of an MIMO antenna configuration at millimeter-wave frequencies. To prove the effectiveness of this method, a five-element nonuniform antenna configuration based on cavity antenna arrays has been designed and tested., acceptedVersion

An ultra compact monostatic two-channel radar MMIC at 160 GHz with enhanced angle estimation accuracy is presented. The MMIC is built up of two transceivers as well as two chip integrated antennas. The small antenna aperture of a quarter wavelength is enhanced by applying a biomimetic antenna array. As a consequence, the MMIC only occupies a chip area of 2.40��1.15 mm��. Radar measurements are performed to evaluate the angle estimation capability of the MMIC and it is shown that the accuracy of the angle estimation is enhanced by a factor of 2.2 by using the biomimetic antenna system., acceptedVersion

Physical unclonable functions (PUFs) are excellent candidates to generate secret information on-chip without the need for secure storage. Ring-oscillator (RO) based PUFs have been receiving great attention over the years due to their easy design and superior statistical characteristics on field pro- grammable gate arrays (FPGAs). Although previous work has improved their statistical measures and provided deeper insights, there are still gaps to be filled. Therefore, this work presents an in-depth analysis of RO-PUFs on Xilinx Zynq-7000 FPGAs with a framework based on partial reconfiguration. This approach allows for full-chip characterization of 100% of the targeted area. Based on the measured data and beforehand estimated routing delay, we will show how to identify and avoid potential bias in the final PUF placement. By utilizing DSP48 slices, an enhanced counter was designed for high-frequency measurements. A second feedback path was added to the ring-oscillators in order to avoid glitches at the counters input. In combination with a reference normalization, the frequency standard deviation could be reduced to 0.0229% at a much shorter evaluation time of 10��s compared to the state-of-the-art, while maintaining the maximum inter-hamming distance. An investigation on the influence of spatial distribution on different RO pairings was performed. The chip variations were found to have a much larger effect on the statistical measures than the difference between logic elements. The measurement data and the framework will be made accessible to interested researchers to provide them with a data basis for further research., acceptedVersion

One common problem of frequency modulated continuous wave radar is leakage from the transmitter to the receiver. The leakage power is orders of magnitude larger than the target return power and appears as a very strong signal in the first few range bins. Additionally, the residual phase noise density of the local oscillator occurs around the leakage signal, which often raises the noise floor and limits the dynamic range of a radar system at the close proximity of the sensor. In this paper a novel system concept that cancels the phase noise around the dominating leakage path is proposed, mathematically derived, and proven by radar measurements with a radar demonstrator at 77 GHz., acceptedVersion

Humanitarian demining is still mainly carried out by hand. The most trusted and widely used technical tool is probably the metal detector. However, these sensors are hand-held devices which are operated closely to the surface. To make the process of mine clearance safer, a ground penetrating synthetic aperture radar (GPSAR) was developed that can be operated on an autonomous flying unmanned aerial system (UAS). A key challenge of this system approach is the accurate position acquisition of the UAS. This paper compares a real time kinematic global navigation satellite system (RTK GNSS) and a total station with respect to UAS-based synthetic aperture radar (SAR) image processing. First, the systems and the associated signal processing chain will be briefly presented, then the trajectories and the processed SAR image will be compared., acceptedVersion

Physical Unclonable Functions (PUFs) offer the possibility to produce unique fingerprints for integrated circuits. As raw PUF responses are affected by noise, some post-processing steps are necessary. We present a coding chain test framework for PUFs on Field Programmable Gate Arrays. The framework allows easy exchange, evaluation and comparison of different PUF implementations, coding algorithms and other chain modules. For a testing framework, the execution time of the evaluated algorithm is a bottleneck, since a huge amount of runs are supposed to be done. Hence, we additionally present a new type of Reed-Muller decoder hardware architecture using parallel modules to speed up the decoding process. The decoding time could be decreased by 95% in comparison to existing implementations at the cost of 41 times higher slice count., acceptedVersion

Electrical Impedance Spectroscopy (EIS) is a popular method for investigating tissue properties. Implementing the signal generator for EIS measurements with a suitable excitation signal type is thereby one of the two system components. The choice of the excitation signal defines the measurement speed, signal-to-noise ratio (SNR), total area and power consumption of the system, and many more properties. Signal types such as analog single-tone, analog multi-tone, linear feedback shift registers (LFSR), and single-tone Sigma Delta Modulated (SDM) are proposed in the state of the art. In this work an EIS setup is implemented and successfully tested with all the mentioned signal types to evaluate their properties on impedance models as well as in vitro cell layers. It is proposed to combine the SDM with the multi-tone excitation signal yielding a very versatile excitation generator. Multi-tone SDM are as fast as analog multitones, while benefiting from a binary output and thus less system complexity. The implemented EIS setup is used to perform EIS measurement for biological samples. The results show a very good matching with the reference for all the excitation signals., acceptedVersion

In automotive sensor networks the spatial distribution of the radar sensors allows to unveil additional information about the target objects. For example, the different angles to a target provide an increased robustness, and the wide sensor distances allow for a single snapshot motion estimation. This is even possible with single-channel radar sensors, but the reliability of the output highly depends on the condition that single scattering points are jointly detected. This paper presents an algorithm which associates single detections of a target over multiple sensors by utilizing the ego-motion of the vehicle. Further, it is shown how all target detections can be assessed and how reliable detections can be identified to improve subsequent processing steps like target localization. The proposed processing is validated by radar measurements at 77 GHz., acceptedVersion