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The traditional manual inspection is gradually replaced by the unmanned aerial vehicles (UAV) automatic inspection. However, due to the limited computational resources carried by the UAV, the existing deep learning-based algorithm needs a large amount of computational resources, which makes it impossible to realize the online detection. Moreover, there is no effective online detection system at present. To realize the high-precision online detection of electrical equipment, this paper proposes an SSD (Single Shot Multibox Detector) detection algorithm based on the improved Dual network for the images of insulators and spacers taken by UAVs. The proposed algorithm uses MnasNet and MobileNetv3 to form the Dual network to extract multi-level features, which overcomes the shortcoming of single convolutional network-based backbone for feature extraction. Then the features extracted from the two networks are fused together to obtain the features with high-level semantic information. Finally, the proposed algorithm is tested on the public dataset of the insulator and spacer. The experimental results show that the proposed algorithm can detect insulators and spacers efficiently. Compared with other methods, the proposed algorithm has the advantages of smaller model size and higher accuracy. The object detection accuracy of the proposed method is up to 95.1%.

in press

Single-walled carbon nanotubes (SWCNTs) are versatile near infrared (NIR) fluorescent building blocks for biosensors. Their surface is chemically tailored to respond to analytes by a change in fluorescence. However, intensity-based signals are easily affected by external factors such as sample movements. Here, we demonstrate fluorescence lifetime imaging microscopy (FLIM) of SWCNT-based sensors in the NIR. We tailor a confocal laser scanning microscope (CLSM) for NIR signals (>800 nm) and employ time correlated single photon counting of (GT)₁₀-DNA functionalized SWCNTs. They act as sensors for the important neurotransmitter dopamine. Their fluorescence lifetime (>900 nm) decays biexponentially and the longer lifetime component (370 ps) increases by up to 25 % with dopamine concentration. These sensors serve as paint to cover cells and report extracellular dopamine in 3D via FLIM. Therefore, we demonstrate the potential of fluorescence lifetime as a readout of SWCNT-based NIR sensors. in press

The major challenges in producing highly electrically conductive copper films are the oxide content and the porosity of the sintered films. This study developed a multilayer sintering method to remove the copper oxides and reduce copper film porosity. We used a self-built arc discharge reactor to produce copper nanoparticles. Copper nanoparticles produced by arc discharge synthesis have many advantages, such as low cost and a high production rate. Conductive inks were prepared from copper nanoparticles to obtain thin copper films on glass substrates. As demonstrated by scanning electron microscopy analyses and electrical resistivity measurements, the copper film porosity and electrical resistivity cannot be significantly reduced by prolonged sintering time or increasing single film thickness. Instead, by applying the multilayer sintering method, where the coating and sintering process was repeated up to four times in this study, the porosity of copper films could be effectively reduced from 33.6% after one-layer sintering to 3.7% after four-layer sintering. Copper films with an electrical resistivity of 3.49 ± 0.35 μΩ·cm (two times of the bulk copper) have been achieved after four-layer sintering, while one-layer sintered copper films were measured to possess resistivity of 11.17 ± 2.17 μΩ·cm.

This paper presents a dataset containing recordings of the electroencephalogram (EEG) and the electromyogram (EMG) from eight subjects who were assisted in moving their right arm by an active orthosis device. The supported movements were elbow joint movements, i.e., flexion and extension of the right arm. While the orthosis was actively moving the subject's arm, some errors were deliberately introduced for a short duration of time. During this time, the orthosis moved in the opposite direction. In this paper, we explain the experimental setup and present some behavioral analyses across all subjects. Additionally, we present an average event-related potential analysis for one subject to offer insights into the data quality and the EEG activity caused by the error introduction. The dataset described herein is openly accessible. The aim of this study was to provide a dataset to the research community, particularly for the development of new methods in the asynchronous detection of erroneous events from the EEG. We are especially interested in the tactile and haptic-mediated recognition of errors, which has not yet been sufficiently investigated in the literature. We hope that the detailed description of the orthosis and the experiment will enable its reproduction and facilitate a systematic investigation of the influencing factors in the detection of erroneous behavior of assistive systems by a large community., Comment: Revised references to our datasets, general corrections to typos, and latex template format changes, Overall Content unchanged

Terahertz time-domain spectroscopy (THz-TDS) is a promising tool for high-resolution 3D imaging of objects due to the high center frequency and bandwidth compared to microwave systems. In addition, terahertz waves have a higher penetration depth than visible or near-infrared radiation. Typically, optics are used to focus the terahertz radiation onto an object under test. This limits the imaging capability in the axial dimension to the depth of field and limits simple imaging of complex surfaces. In this work, we adapt a backpropagation algorithm from synthetic aperture radar (SAR) imaging to reconstruct high-resolution 3D images from time-domain traces acquired with a lensless THz-TDS system. For this purpose, an inverse cylindrical aperture is used and an equation that describes the maximum achievable resolution as a function of the beam pattern, the bandwidth, and the length of the synthetic aperture is derived. The calculated resolution is 960 μ m for the linear dimension of the aperture and 75 μ m for the rotationally symmetric dimension of the cylindrical aperture for a bandwidth of 2 THz. The resolving power is verified by measurements on metallic and dielectric objects. In the future, this method can be used for non-destructive testing of objects with complex shaped surfaces and internal structures. CA Kubiczek

PurposeThe best algorithm that was implemented on this Brazilian dataset was artificial immune system (AIS) algorithm. But the time and cost of this algorithm are high. Using asexual reproduction optimization (ARO) algorithm, the authors achieved better results in less time. So the authors achieved less cost in a shorter time. Their framework addressed the problems such as high costs and training time in credit card fraud detection. This simple and effective approach has achieved better results than the best techniques implemented on our dataset so far. The purpose of this paper is to detect credit card fraud using ARO.Design/methodology/approachIn this paper, the authors used ARO algorithm to classify the bank transactions into fraud and legitimate. ARO is taken from asexual reproduction. Asexual reproduction refers to a kind of production in which one parent produces offspring identical to herself. In ARO algorithm, an individual is shown by a vector of variables. Each variable is considered as a chromosome. A binary string represents a chromosome consisted of genes. It is supposed that every generated answer exists in the environment, and because of limited resources, only the best solution can remain alive. The algorithm starts with a random individual in the answer scope. This parent reproduces the offspring named bud. Either the parent or the offspring can survive. In this competition, the one which outperforms in fitness function remains alive. If the offspring has suitable performance, it will be the next parent, and the current parent becomes obsolete. Otherwise, the offspring perishes, and the present parent survives. The algorithm recurs until the stop condition occurs.FindingsResults showed that ARO had increased the AUC (i.e. area under a receiver operating characteristic (ROC) curve), sensitivity, precision, specificity and accuracy by 13%, 25%, 56%, 3% and 3%, in comparison with AIS, respectively. The authors achieved a high precision value indicating that if ARO detects a record as a fraud, with a high probability, it is a fraud one. Supporting a real-time fraud detection system is another vital issue. ARO outperforms AIS not only in the mentioned criteria, but also decreases the training time by 75% in comparison with the AIS, which is a significant figure.Originality/valueIn this paper, the authors implemented the ARO in credit card fraud detection. The authors compared the results with those of the AIS, which was one of the best methods ever implemented on the benchmark dataset. The chief focus of the fraud detection studies is finding the algorithms that can detect legal transactions from the fraudulent ones with high detection accuracy in the shortest time and at a low cost. That ARO meets all these demands.

In dieser Arbeit werden kompakte Induktionsspulen als berührungslose elektroma- gnetische Ultraschallwandler (EMATs) ohne zusätzliche Magnete untersucht. Im Vergleich dazu sind klassische, kommerziell verfügbare EMATs auf die Verwendung von voluminösen Permanentmagneten oder separaten Elektromagneten angewiesen. Die Vorteile der EMATs ohne zusätzliche Magnete sind höhere magnetische Flussdichten lokal am Wirkungsort, keine störende Anziehung von ferromagnetischen Fremdobjekten und deutlich kleinere Sensorköpfe, was eine wichtige Voraussetzung für die Herstellung von kompakten EMAT-Phased-Arrays ist. Die Umsetzung solcher EMATs stellt eine Herausforderung dar, weil die Elektronik für die Ultraschallerzeugung mit Spannungen und Strömen im kV- und kA-Bereich umgehen muss. Aufgrund des bei EMATs generell geringen Wirkungsgrads müssen beim Ultraschallempfang Signale im unteren µV-Bereich detektiert werden. Gleichzeitig dürfen keine Störungen durch die impulsartigen kA-Ströme entstehen und die relativ kleinen EMAT-Induktoren, die als Sensorköpfe dienen, müssen den oft wiederholten kA-Impulsen standhalten. Für die Auslegung von EMATs ohne zusätzliche Magnete werden Modellbildungen für die Magnetfeld- und Schallfeldberechnung gezeigt. Als Demonstrationsszenario wird eine 3D-Lokalisierung einer Inhomogenität im Inneren eines mit Flüssigkeit gefüllten dickwandigen Metallbehälters ohne mechanischen Kontakt zum Behälter (1 mm Luftspalt) erfolgreich durchgeführt. Weiterhin wird eine berührungslose Kantenabtastung einer ferromagnetischen Stahlplatte mit unidirektionalen Lamb-Wellen präsentiert. Die Lamb-Wellen werden mit kontrollierten Interferenzeffekten unidirektional ausgesendet und empfangen. Der kompakte Aufbau des phasengenauen Doppel-EMATs bestätigt die Machbarkeit von Phased-Arrays. Des Weiteren wird gezeigt, wie der Ultraschallempfang mit einem EMAT auf einem ferromagnetischen Prüfkörper ohne eine aktive Magnetisierung (Bias-Magnetfeld) möglich ist. Somit wird die Problematik des zeitlich begrenzten (µs-Bereich) Bias-Magnetfeldes gelöst, wodurch sich deutlich längere (ms- bis s-Bereich) Empfangszeitfenster realisieren lassen. Ohne die Verwendung einer aktiven Magnetisierung entfallen auch Probleme wie das Auftreten von Barkhausenrauschen oder Signalstörungen durch Schaltvorgänge von Dioden zum Schutz vor Polaritätsumkehr der Elektrolytkondensatorbänke. Es entstehen mehr Freiheitsgrade, wodurch neuartige EMAT-Konzepte vorstellbar sind, die flächige Induktoren und Ferritrückplatten mit hohen relativen Permeabilitätszahlen verwenden. Dissertation, Universität Duisburg-Essen, 2023

With the advancement of technology, shielding for terahertz (THz) electronic and communication equipment is increasingly important. The metamaterial absorption technique is mostly used to shield electromagnetic interference (EMI) in THz sensing technologies. The most widely used THz metamaterial absorbers suffer from their narrowband properties and the involvement of complex fabrication techniques. Materials with multifunctional properties, such as adjustable conductivity, broad bandwidth, high flexibility, and robustness, are driving future development to meet THz shielding applications. In this article, a theoretical simulation approach based on finite difference time domain (FDTD) is utilized to study the absorption and shielding characteristics of a two-dimensional (2D) MXene Ti₃C₂Tₓ metasurface absorber in the THz band. The proposed metamaterial structure is made up of a square-shaped array of MXene that is 50 nm thick and is placed on top of a silicon substrate. The bottom surface of the silicon is metalized with gold to reduce the transmission and ultimately enhance the absorption at 1–3 THz. The symmetric adjacent space between the MXene array results in a widening of bandwidth. The proposed metasurface achieves 96% absorption under normal illumination of the incident source and acquires an average of 25 dB shielding at 1 THz bandwidth, with the peak shielding reaching 65 dB. The results show that 2D MXene-based stacked metasurfaces can be proven in the realization of low-cost devices for THz shielding and sensing applications. CA extern

Großflächig lichtemittierende Bauelemente auf Basis von 2D-Halbleitern Zweidimensionale (2D) Materialien stellen eine spannende neue Materialklasse mit metallischen, halbleitenden und isolierenden Eigenschaften dar. Atomar dünne Übergangsmetall-Dichalcogenide (TMDCs), insbesondere die Familie (Mo, W)(S, Se)2, haben in den letzten Jahren großes Interesse geweckt. Liegen diese 2D-Halbleiter als Monolage mit einer Schichtdicke < 0,7 nm vor, weisen sie eine direkte Bandlücke auf und besitzen eine große Oszillatorstärke, was sie zu vielversprechenden Kandidaten für zukünftige optoelektronische Anwendungen macht. In der Theorie können alle 2D-Materialien frei kombiniert werden, ohne durch Wachstumsprozesse und Gitterkonstanten eingeschränkt zu sein. Um jedoch TMDCs als 2D-Bausteine für ultradünne lichtemittierenden Bauelemente der nächsten Generation nutzen zu können, gibt es jedoch noch einige Herausforderungen zu überwinden: Bisher zeigen nur wenige Ansätze die Möglichkeit einer Skalierung für die Herstellung im größeren Maßstab, die für praktische Anwendungen relevant ist. Da auch die kontrollierte Herstellung von TMDCs noch immer eine große Herausforderung ist, würde die Kombination eines reproduzierbaren Herstellungsverfahrens mit einer geeigneten skalierbaren Bauelementarchitektur den nächsten Schritt in Richtung 2D-Optoelektronik ebnen. Das in dieser Arbeit entwickelte Grundkonzept lichtemittierender Bauelemente beruht dabei auf einem vollständig vertikalen Design, wodurch dieses prinzipiell beliebig skalierbar ist. Dieser Ansatz basiert auf der Einbettung von WS2-Monolayern in ein p-i-n-Layout unter Verwendung organischen p- und anorganischen n-Hilfsschichten. In einer ersten Machbarkeitsstudie wurden exfolierte WS2-Monolagen verwendet, wobei der Strompfad mittels Laserlithografie senkrecht zur WS2-Flocke definiert wurde. Diese Bauelemente weisen ein diodisches I-U-Verhalten auf und die Elektrolumineszenz (EL) erreicht bei Raumtemperatur eine Leuchtdichte von bis zu 50 cd m-2 im roten Spektralbereich. Um dieses Bauelementkonzept zu skalieren, ist ein großflächiges TMDC-Wachstum mit homogenen Eigenschaften erforderlich. Dafür wird zunächst MoS2 untersucht, das auf 2 ‘‘ Saphir (0001) Wafern mittels metallorganischer Gasphasenabscheidung (MOCVD) gewachsen ist. Hier wird der Zusammenhang zwischen den Wachstumsparametern und der Photolumineszenz (PL) Intensität analysiert. Dabei konnte eine klare Korrelation zwischen der Kristallkorngröße und der PL-Intensität festgestellt werden. Eine Verringerung der Halbwertsbreiten sowohl der Raman-Resonanzen als auch der PL-Spektren wies darüber hinaus auf eine verringerte Defektdichte bei optimierten Wachstumsbedingungen hin. Eine Transfertechnik wurde entwickelt, um großflächig gewachsene WS2-Monolagen in die vertikale p-i-n-Bauelementarchitektur einzubetten. Bei Anlegen einer Spannung zeigten die prozessierten Bauelemente ein gleichrichtendes Verhalten und eine rote EL über eine Fläche von 6 mm2, die nur durch die Größe der Kontaktpads begrenzt ist. Es wurden Einschaltspannungen < 2,5 V erreicht und bei einer Betriebsspannung von 7 V konnte eine Leuchtdichte von fast 1 cd m2 erzielt werden. Durch die erfolgreiche Umsetzung dieses Konzepts auf Foliensubstraten wurden die ersten flexiblen, großflächigen lichtemittierenden Bauelemente auf der Basis von 2D-Halbleitern realisiert. Eine Besonderheit dieser Bauteile ist, dass durch einfaches Biegen eine Verspannung des WS2-Kristalls hervorgerufen werden kann und somit die Farbe der Lichtemission mit -30 meV ε(%)‑1 verändert werden kann., Large scale light-emitting devices based on 2D semiconductors Two-dimensional (2D) materials represent an exciting new material class of conductors, semiconductors, and insulators. Atomically thin transition metal dichalcogenides (TMDCs), in particular the family (Mo, W)(S, Se)2, have attracted tremendous interest in recent years. Forming a direct bandgap for monolayer thickness (< 0.7 nm) and exhibiting exceptional excitonic effects, these 2D semiconductors represent promising compounds for future applications. Due to their naturally passivated surfaces and out-of-plane van der Waals interactions, TMDCs can be used to form heterostructures without lattice constraints. Consequently, TMDCs can serve as 2D building blocks for next-generation ultrathin optoelectronic devices. However, there are still main challenges on the route toward practical light-emitting devices based on TMDC materials: Although, various approaches toward light-emitting devices, e.g., based on exfoliated or chemical vapor deposited TMDC monolayers, have been reported, they all suffer from limited scalability and reproducibility required for industrial fabrication. Furthermore, the controlled fabrication of TMDCs is still a daunting challenge. Combining a scalable and reproducible fabrication route with a suitable and mature device architecture for light-emitting devices would be the next step toward 2D optoelectronics. Here, a novel LED architecture with a vertical and therefore scalable design is developed. This approach is based on embedding WS2 monolayers into a p-i–n layout using organic p- and inorganic n-supporting layers. In a first step of proof-of-concept, exfoliated WS2 monolayers were used. Laser lithography was applied to define the current path perpendicular to the WS2 flake. These devices exhibit diode-like behavior and emit room temperature electroluminescence (EL) with luminance up to 50 cd m−2 in the red spectral range. Scaling this device concept from the lab towards industrial relevant sizes, a large-scale TMDC growth with homogeneous properties is necessary. Serving this, MoS2 grown on 2 ’’ sapphire (0001) wafers via metal organic chemical vapor deposition (MOCVD) are used. Here the relation between growth parameters and photoluminescence (PL) intensity, as one of the most important parameters for optoelectronic applications, will be discussed. A prebake step under H2 atmosphere combined with a reduced molybdenum precursor flow increases the crystal grain size by one order of magnitude and strongly enhances PL intensity with a clear correlation to the grain size. A decrease of the linewidths of both, Raman resonances and PL spectra, indicate a reduced defect density at optimized growth conditions. A transfer technique was developed to embed MOCVD WS2 monolayers into the vertical p-i‑n device architecture. Those devices show a rectifying behavior in I-V measurements. With an applied voltage, red EL over an area of 6 mm2 was observed, which is just limited by the size of the contact pads. A turn-on voltage of less than 2.5 V has been achieved, and a luminance of almost 1 cd m2 was obtained at a bias voltage of 7 V. By successful implementation of this concept onto foil substrates, the first large-area flexible light-emitting devices based on 2D materials were realized. Uniquely, the strong dependence of the WS2 bandgap on strain results in a tunable EL emission with a gauge factor of -30 meV ε(%)-1 simply by bending the device. These results pave the way to large-area 2D light-emitting devices that are easily processable and scalable for future ultrathin and flexible light concepts.

in press, CA Sheikh In this paper, new concepts for continuous 24/7 real-time monitoring of plants and insects with miniaturized terahertz (THz) systems are described and experimentally tested. Thus, for the first time, small-scale insights into the instantaneous plant health but also in their long-term growth can be obtained. Using such compact THz systems, e.g. water uptake, insect infestation and the behavior of pollinators (i.e. honey bees) and pests can be measured dynamically and non-invasively at virtually any position in the close biotope surrounding them. In addition to general understanding, this can be used to optimize crop yield and reduce resource consumption as well as for identifying characteristics of insect-plant interactions induced by potential environmental stressors. Given such holistic a approach, the proposed concepts may provide a significant advancement in environmental monitoring technology.

Here we present an artificial neural network (ANN)-approach to determine the fractional contributions Pi from fluorophores to a multi-exponential fluorescence decay in time-resolved lifetime measurements. Conventionally, Pi are determined by extracting two parameters (amplitude and lifetime) for each underlying mono-exponential decay using non-linear fitting. However, in this case parameter estimation is highly sensitive to initial guesses and weighting. In contrast, the ANN-based approach robustly gives the Pi without knowledge of amplitudes and lifetimes. By experimental measurements and Monte-Carlo simulations, we comprehensively show that accuracy and precision of Pi determination with ANNs and hence the number of distinguishable fluorophores depend on the fluorescence lifetimes’ differences. For mixtures of up to five fluorophores, we determined the minimum uniform spacing Δτmin between lifetimes to obtain fractional contributions with a standard deviation of 5%. In example, five lifetimes can be distinguished with a respective minimum uniform spacing of approx. 10 ns even when the fluorophores’ emission spectra are overlapping. This study underlines the enormous potential of ANN-based analysis for multi-fluorophore applications in fluorescence lifetime measurements.

Transition metal dichalcogenide (TMDC) monolayers with their direct band gap in the visible to near-infrared spectral range have emerged over the past years as highly promising semiconducting materials for optoelectronic applications. Progress in scalable fabrication methods for TMDCs like metal-organic chemical vapor deposition (MOCVD) and the ambition to exploit specific material properties, such as mechanical flexibility or high transparency, highlight the importance of suitable device concepts and processing techniques. In this work, we make use of the high transparency of TMDC monolayers to fabricate transparent light-emitting devices (LEDs). MOCVD-grown WS₂ is embedded as the active material in a scalable vertical device architecture and combined with a silver nanowire (AgNW) network as a transparent top electrode. The AgNW network was deposited onto the device by a spin-coating process, providing contacts with a sheet resistance below 10 Ω sq−¹ and a transmittance of nearly 80%. As an electron transport layer we employed a continuous 40 nm thick zinc oxide (ZnO) layer, which was grown by atmospheric pressure spatial atomic layer deposition (AP-SALD), a precise tool for scalable deposition of oxides with defined thickness. With this, LEDs with an average transmittance over 60% in the visible spectral range, emissive areas of several mm² and a turn-on voltage of around 3 V are obtained.

Carbon : an international journal sponsored by the American Carbon Society 201, 189-199 (2023). doi:10.1016/j.carbon.2022.09.002, Published by Elsevier Science, Amsterdam [u.a.]

A holistic simulation of a photovoltaic system requires multiple physical levels - the optoelectronic behavior of the semiconductor devices, the conduction of the generated current, and the actual operating conditions, which rarely correspond to the standard testing conditions (STC) employed in product qualification. We present a holistic simulation approach for all thin-film photovoltaic module technologies that includes a transfer-matrix method, a drift-diffusion model to account for the p-n junction, and a quasi-three-dimensional finite-element Poisson solver to consider electrical transport. The evolved digital model enables bidirectional calculation from material parameters to non-STC energy yield and vice versa, as well as accurate predictions of module behavior, time-dependent top-down loss analyses and bottom-up sensitivity analyses. Simple input data like current-voltage curves and material parameters of semiconducting and transport layers enables fitting of otherwise less-defined values. The simulation is valuable for effective optimizations, but also for revealing values for difficult-to-measure parameters.

We fabricated superconducting and ferromagnetic nanostructures, which are intended for applications in transmission electron microscopy (TEM), in a commercial sample holder that can be cooled using liquid helium. Nanoscale superconducting quantum-interference devices (nanoSQUIDs) with sub-100 nm nanobridge Josephson junctions (nJJs) were prepared at a distance of ~300 nm from the edges of a 2 mm × 2 mm × 0.05 mm substrate. Thin-film TiN-NbN-TiN heterostructures were used to optimize the superconducting parameters and enhance the oxidation and corrosion resistance of nJJs and nanoSQUIDs. Non-hysteretic I(V) characteristics of nJJs, as well as peak-to-peak quantum oscillations in the V(B) characteristics of the nanoSQUIDs with an amplitude of up to ~20 µV, were obtained at a temperature ~5 K, which is suitable for operation in TEM. Electron-beam lithography, high-selectivity reactive ion etching with pure SF6 gas, and a naturally created undercut in the Si substrate were used to prepare nanoSQUIDs on a SiN membrane within ~500 nm from the edge of the substrate. Permalloy nanodots with diameters down to ~100 nm were prepared on SiN membranes using three nanofabrication methods. High-resolution TEM revealed that permalloy films on a SiN buffer have a polycrystalline structure with an average grain dimension of approximately 5 nm and a lattice constant of ~0.36 nm. The M(H) dependences of the permalloy films were measured and revealed coercive fields of 2 and 10 G at 300 and 5 K, respectively. These technologies are promising for the fabrication of superconducting electronics based on nJJs and ferromagnetic nanostructures for operation in TEM.

CA extern

Not all research leads to fruitful results; trying new ways or methods may surpass state of the art, but sometimes the hypothesis is not proven, the improvement is insignificant, or the system fails because of a design error done years ago in previous works. In a systems discipline like pervasive computing, there are many sources of errors, from hardware issues over communication channels to heterogeneous software environments. However, failure to succeed is not a failure to progress. It is essential to create platforms for sharing insights, experiences, and lessons learned when conducting research in pervasive computing so that the same mistakes are not repeated. And sometimes, a problem is a symptom of discovering new research challenges. Based on the collective input of the First International Workshop on Negative Results in Pervasive Computing (PerFail 2022), co-located with the 20th International Conference on Pervasive Computing and Communications (PerCom 2022), this article presents a comprehensive discussion on perspectives on publishing negative results, useful failures, and lessons learned in pervasive computing.

IFToMM D-A-CH Konferenz, vol. 2023

This article deals with the recursive filtering issue for an array of two-dimensional systems with random sensor failures and dynamic quantizations. The phenomenon of sensor failure is introduced whose occurrence is governed by a random variable with known statistical properties. In view of the data transmission over networks of constrained bandwidths, a dynamic quantizer is adopted to compress the raw measurements into the quantized ones. The main objective of this article is to design a recursive filter so that a locally minimal upper bound is ensured on the filtering error variance. To facilitate the filter design, states of the dynamic quantizer and the target plant are integrated into an augmented system, based on which an upper bound is first derived on the filtering error variance and subsequently minimized at each step. The expected filter gain is parameterized by solving some coupled difference equations. Moreover, the monotonicity of the resulting minimum upper bound with regard to the quantization level is discussed and the boundedness analysis is further investigated. Finally, effectiveness of the developed filtering strategy is verified via a simulation example. This work was supported in part by the National Natural Science Foundation of China under Grants 61903082, 61873148 and 61933007, the University of Macau under UM Macao Talent Programme (UMMTP-2020-01), the Macau Science and Technology Development Fund under Grant FDCT/0146/2019/A3, the Project MYRG2020-00188-FST of the University of Macau, the Fundação para a Ciência e a Tecnologia (FCT), Portugal through LARSyS-FCT Project UIDB/50009/2020, the China Postdoctoral Science Foundation under Grant 2022M710683, the Jiangsu Funding Program for Excellent Postdoctoral Talent of China under Grant 2022ZB128, the Fundamental Research Funds for the Central Universities of China under Grant 2242022R20032, and the Alexander von Humboldt Foundation of Germany.

A one-dimensional analytical model of charge transfer in charge-coupled devices, which describes the spatial-temporal behavior of the charge carrier density in a potential well, is presented. The general solution of this model considers the transfer dynamics in terms of the electric drift field, i.e., self-induced drift and fringing-field drift, and yields an analytical solution for the total number of charge carriers. A comparison of the transfer efficiency for various electric drift fields is presented. The modulation transfer function in dependence on the transfer efficiency is analyzed, aiming especially at time-delay integration (TDI) applications. Finally, the results of this model are concluded and discussed in detail.

The chemical synthesis of (CdSe)13 magic-sized clusters (MSCs) allows the replacement of host atoms by individual transition metals such as Mn. By analyzing the spectral fingerprints of the Mn2+ photoluminescence (PL) in MSCs with different dopant concentrations, we are able to distinguish between single Mn2+ ions and coupled Mn2+ pairs. In case of Mn2+ pair emission, temperature-dependent studies show a pronounced red shift, followed by a distinct blue shift of the PL energy upon heating. This is related to a spin ladder formation of the ground and excited states due to Mn2+-Mn2+ exchange interaction at cryogenic temperatures, which is assumed to vanish at higher temperatures. In contrast, single Mn2+ ion PL exhibits a unique redshift with increasing temperature, which can be attributed to a particularly strong coupling to vibronic modes due to the ultimate small size of the MSCs.

Prospects and challenges for mobile 6G communications using terahertz frequencies are discussed. For the first time, THz wireless communications with 15 Gbps to multiple mobile users employing a photonic-assisted beam steering antennas is experimentally demonstrated.

Thermoelectric generators (TEGs) possess the ability to generate electrical power from heat. As TEGs are operated under a thermal gradient, inhomogeneous material properties—either by design or due to inhomogeneous material degradation under thermal load—are commonly found. However, this cannot be addressed using standard approaches for performance analysis of TEGs in which spatially homogeneous materials are assumed. Therefore, an innovative method of analysis, which can incorporate inhomogeneous material properties, is presented in this study. This is crucial to understand the measured performance parameters of TEGs and, from this, develop means to improve their longevity. The analysis combines experimental profiling of inhomogeneous material properties, modelling of the material properties using a single parabolic band model, and calculation of device properties using the established Constant Property Model. We compare modeling results assuming homogeneous and inhomogeneous properties to the measurement results of an Mg₂(Si,Sn)-based TEG prototype. We find that relevant discrepancies lie in the effective temperature difference across the TE leg, which decreases by ~10%, and in the difference between measured and calculated heat flow, which increases from 2–15% to 9–16% when considering the inhomogeneous material. The approach confirms additional resistances in the TEG as the main performance loss mechanism and allows the accurate calculation of the impact of different improvements on the TEG’s performance. CA de Boor

in press

Atrial Fibrillation (AF) is one of the most common heart arrhythmias. It is known to cause up to 15% of all strokes. In current times, modern detection systems for arrhythmias, such as single-use patch electrocardiogram (ECG) devices, have to be energy efficient, small, and affordable. In this work, specialized hardware accelerators were developed. First, an artificial neural network (NN) for the detection of AF was optimized. Special attention was paid to the minimum requirements for the inference on a RISC-V-based microcontroller. Hence, a 32-bit floating-point-based NN was analyzed. To reduce the silicon area needed, the NN was quantized to an 8-bit fixed-point datatype (Q7). Based on this datatype, specialized accelerators were developed. Those accelerators included single-instruction multiple-data (SIMD) hardware as well as accelerators for activation functions such as sigmoid and hyperbolic tangents. To accelerate activation functions that require the e-function as part of their computation (e.g., softmax), an e-function accelerator was implemented in the hardware. To compensate for the losses of quantization, the network was expanded and optimized for run-time and memory requirements. The resulting NN has a 7.5% lower run-time in clock cycles (cc) without the accelerators and 2.2 percentage points (pp) lower accuracy compared to a floating-point-based net, while requiring 65% less memory. With the specialized accelerators, the inference run-time was lowered by 87.2% while the F1-Score decreased by 6.1 pp. Implementing the Q7 accelerators instead of the floating-point unit (FPU), the silicon area needed for the microcontroller in 180 nm-technology is below 1 mm (Formula presented.). CA extern

Many countries around the world face a shortage of medical personnel, leading to work overload or even burnout. This calls for political and scientific solutions to relieve the medical personnel. The measurement of vital signs in hospitals is still predominately carried out manually with traditional contact-based methods, taking over a substantial share of the medical personnel’s workload. The introduction of contactless methods for vital sign monitoring (e.g., with a camera) has great potential to relieve the medical personnel. This systematic review’s objective is to analyze the state of the art in the field of contactless optical patient diagnosis. This review distinguishes itself from already existing reviews by considering studies that do not only propose the contactless measurement of vital signs but also include an automatic diagnosis of the patient’s condition. This means that the included studies incorporate the physician’s reasoning and evaluation of vital signs into their algorithms, allowing an automated patient diagnosis. The literature screening of two independent reviewers resulted in a total of five eligible studies. The highest number of studies (three) introduce methods for the risk assessment of infectious diseases, one study introduces a method for the risk assessment of cardiovascular diseases, and one study introduces a method for the diagnosis of obstructive sleep apnea. Overall, high heterogeneity in relevant study parameters is reported among the included studies. The low number of included studies indicates a large research gap and emphasizes the demand for further research on this emerging topic. CA Alic

In diesem Artikel wird zunächst exemplarisch aufgezeigt, welche differenzierten Möglichkeiten und Zugänge bestehen, einen Seifenblasenautomaten im Unterricht zu fertigen. Im Anschluss daran wird mittels einer detaillierten Schritt-für-Schritt-Anleitung die Fertigung einer Seifenblasenautomaten- Variante vorgestellt, die unterschiedliche Fertigungsverfahren und Planungsmittel bei der Umsetzung aufgreift. (DIPF/Orig.)

The energetic disorder has been known for decades to limit the performance of structurally disordered semiconductors such as amorphous silicon and organic semiconductors. However, in the past years, high-performance organic solar cells have emerged showing a continuously reduced amount of energetic disorder. While searching for future high-efficiency material systems, it is therefore important to correctly characterize this energetic disorder. While there are several techniques in the literature, the most common approaches to probe the density of defect states are using optical excitation as in external quantum efficiency measurements, or sequential filling of the tail states by applying an external voltage as in admittance spectroscopy. A metanalysis of available literature, as well as the experiments using four characterization techniques on two material systems, reveal that electrical, voltage-dependent measurements frequently yield higher values of energetic disorder than optical measurements. With drift-diffusion simulations, it is demonstrated that the approaches probe different energy ranges of the subband-gap density of states. The limitations of the techniques are further explored and it is found that extraction of information from a capacitance-voltage curve can be inhibited by internal series resistance. Thereby, the discrepancies between measurement techniques with sensitivity to different energy ranges and electronic parameters are explained.

An indium phosphide (InP)-based E-plane transition for monolithically integrating terahertz photodiodes with standard rectangular waveguide (WR)-outputs is presented for all standard WR-frequency bands from 0.22 THz to 2.2 THz, i.e., from WR3 to WR0.51. The integration concept comprises a modified uni-travelling carrier photodiode (MUTC-PD) chip, an E-plane transition and a stepped impedance low-pass filter (LPF), which are all monolithically integrated on InP substrate. The E-plane transition converts the quasi-TEM coplanar waveguide (CPW) mode of the MUTC-PD output to the dominant TE10 mode of the WR. To our knowledge, this is the first frequency-scalable monolithic integration concept that enables packaging of photodiodes with standard WR-outputs up to 2.2 THz. The recommended thickness of the InP substrate and the proposed E-plane transitions design parameters are investigated by numerical analysis to achieve minimum insertion loss (IL) and a wide operational bandwidth (BW). The presented optimized transitions exhibit a maximum IL of 1.4 dB, a return loss (RL) better than 10 dB and a minimum 1 dB IL BW of 92.23% for all WR-bands up to 2.2 THz. To prove the proposed monolithic integration concept, a MUTC-PD is integrated with a CPW-to-WR3 E-plane transition (220-320 GHz) on a 95 m-thick InP substrate. At 300 GHz, the maximum achieved RF output power of the fabricated MUTC-PD chip is -12.4 dBm at a photocurrent of 18.5 mA. For experimental characterization, the MUTC-PD chip with the integrated E-plane transition has been mounted on a 1 mm-thick soda-lime glass substrate as carrier and it has been manually aligned within a WR-3 together with an adjustable back-short. Due to non-perfect alignment of the chip and the back-short as well as the additional losses and substrate modes due to the thick glass carrier, the calculated average IL is increased to 5.3 dB. Experimentally, an average IL of 8.6 dB is measured within the WR3-band from 220 GHz to 320 GHz. Integration of the chip in a real package without misalignment and without the glass carrier is expected to improve the IL by ~4.8 dB. in press

This paper investigates the finite-time cooperative formation control problem for a heterogeneous system consisting of an unmanned ground vehicle (UGV) - the leader and an unmanned aerial vehicle (UAV) - the follower. The UAV system under consideration is subject to modeling uncertainties, external disturbance as well as actuator faults simultaneously, which is associated with aerodynamic and gyroscopic effects, payload mass, and other external forces. First, a backstepping controller is developed to stabilize the leader system to track the desired trajectory. Second, a robust nonsingular fast terminal sliding mode surface is designed for UAV and finite-time position control is achieved using terminal sliding mode technique, which ensures the formation error converges to zero in finite time in the presence of actuator faults and other uncertainties. Furthermore, by combining the radial basis function neural networks (NNs) with adaptive virtual parameter technology, a novel NN-based adaptive nonsingular fast terminal sliding formation controller (NN-ANFTSMFC) is developed. By means of the proposed adaptive control strategy, both uncertainties and actuator faults can be compensated without the prior knowledges of the uncertainty bounds and fault information. By using the proposed control schemes, larger actuator faults can be tolerated while eliminating control chattering. In order to realize fast coordinated formation, the expected position trajectory of UAV is composed of the leader position information and the desired relative distance with UGV, based on local distributed theory, in the three-dimensional space. The tracking and formation controllers are proved to be stable by the Lyapunov theory and the simulation results demonstrate the effectiveness of proposed algorithms.

This paper presents an analytical and numerical investigation of the radiation features of an interesting class of electromagnetic bandgap (EBG) structures excited by an electric line source. The radiation from two-dimensional (2-D) lattices made with lossless dielectric cylinders, typically optimized by using the Bloch analysis of the corresponding 2-D photonic crystals, are originally investigated in terms of leaky waves. A thorough modal analysis of open waveguides, composed by a finite number of periodic chains of circular dielectric rods, is presented that shows a multiplicity of bound and leaky modes. Two radiation windows are identified and the relevant directive features are described in terms of properly excited dominant leaky modes. The possible excitation of higher order leaky modes and guided modes has been carefully considered, by also capturing the relevant residue contributions in a nonspectral representation of the excited fields. The final results on radiated fields by realistic truncated structures, obtained by ad-hoc software as well as full-wave EM simulators, are in excellent agreement with those predicted by the proposed leaky-wave approach.

Introduction Myalgic encephalomyelitis (ME) / chronic fatigue syndrome (CFS) is a disease of the nervous system that leads to profound physical weakness. The number of patients is currently increasing worldwide due to the consequences of chronic COVID-19 syndrome. ME/CFS patients suffer from severe fatigue, autonomic, neurological and immunological symptoms. The core symptom Post-Exertional Malaise (PEM) leads to a general exacerbation after even low levels of exertion. Since there is no approved therapy, patient advocacy groups recommend pacing. This involves monitoring trivial vital signs of the patient to avoid PEM. This paper aims to evaluate the suitability of various vital signs and proposes matching sensors. Methods Via a literature review, different vital signs are compared in terms of their usefulness for PEM prevention. Objective criteria such as the number of publications and the PEM triggers to be covered are included in the evaluation. Recommendations for the use of body-worn sensors are derived from the vital signs and the requirements for real-world use. This takes into account patient needs through an objective evaluation of, among other things, wearer comfort, long-term stability and attachment. Results Even simple pedometers can help to monitor the physical trigger of PEM. Strong emotional reactions can be detected by heart rate monitoring. This can be accomplished using electrocardiography and photoplethysmopgraphy sensors. Smartwatches and chest straps in particular are suitable for easy monitoring of vital signs because they enable long-term measurement without interruption and easy sensor attachment. Conclusion The importance of different vital parameter sensors in the monitoring of PEM is elaborated. In the future, more complex analysis of heart rate variability and respiratory rate could be used to prevent PEM. From this, recommendations for the prevention of PEM and potential Long-Covid consequences can be derived. This may help to mitigate the severity of the disease course.

CA extern Initiated three decades ago, integrated design of controllers and fault detectors has continuously attracted research attention. The recent development of the unified control and detection framework with an observer-based residual generator in its core gives a more general form of the previous works. Its applications to residual centred modelling of uncertain control systems, fault detection in feedback control systems with uncertainties, fault-tolerant control (FTC) as well as control performance degradation monitoring, detection and recovery are introduced. In conclusion, some future perspectives are proposed.

In this work, we present an optically subharmonic pumped WR3-mixer for enabling photonic coherent frequency-domain terahertz (THz) imaging and spectroscopy systems in the future. The studied mixer operates within the upper range of the WR3-band from 270 GHz to 320 GHz. High-power uni-travelling carrier photodiodes (UTC-PDs) are developed for providing the subharmonic local oscillator (LO) signal within the corresponding WR6-band in the range between 135 GHz and 160 GHz. The proposed THz mixer module consists of a gallium arsenide (GaAs)-based low barrier Schottky diodes (LBSDs) chip and an indium phosphide (InP)-based UTC-PD chip. For integrating the UTC-PD with the WR6 at the mixer’s LO input, an E-plane transition and a stepped-impedance microstrip line low pass filter (MSL-LPF) are developed and monolithically integrated with the UTC-PD chip on a 100 µm thick InP substrate. The E-plane transition converts the quasi-TEM mode of the grounded coplanar waveguide (GCPW) to the dominant TE10 mode of the WR6 and matches the GCPW’s impedance with the WR6’s impedance. According to full-wave EM simulations, the transition exhibits a 1 dB bandwidth (BW) of more than 30 GHz (138.8-172.1 GHz) with a corresponding return loss (RL) better than 10 dB, whereas the minimum insertion loss (IL) is 0.65 dB at a frequency of 150 GHz. Experimentally, the 1 dB BW of the fabricated transition is found to be between 140 GHz and 170 GHz, which confirms the numerical results. The minimum measured IL is 2.94 dB, i.e., about 2 dB larger than the simulated value. In order to achieve the required LO power for successfully pumping the mixer in a direct approach (i.e., without an additional LO amplifier), the design of the epitaxial system of the UTC-PD is optimized to provide a high output power within the WR6-band (110-170 GHz). Experimentally, at 150 GHz, the output power of the fabricated UTC-PD chip is measured to be +3.38 dBm at a photocurrent of 21 mA. To our knowledge, this is the highest output power ever achieved from a UTC-PD at 150 GHz. Finally, the developed high-power UTC-PDs are used as LO source to pump the subharmonic WR3-mixer. Experimentally, the conversion loss (CL) is determined in dependency of the LO power levels within the RF frequency range between 271 GHz and 321 GHz for a fixed IF at 1 GHz. The achieved results have revealed an inverse relation between the CL and LO power level, where the average minimum CL of 16.8 dB is achieved at the highest applied LO power level, corresponding to a photocurrent of 10 mA. This CL figure is promising and is expected to reach the CL of electronically pumped and commercially available THz mixers (∼12 dB) after packaging the LO source with the mixer. Furthermore, an average CL of 17.2 dB is measured at a fixed LO frequency of 150 GHz and a tuned RF frequency between 301 GHz and 310 GHz, i.e., IF between 1 GHz and 10 GHz.

We report on the nanoparticle-size-dependent onset of quantum tunneling of electrons across the subnanometer gaps in three different sizes (30, 50, and 80 nm) of highly uniform gold nanosphere (AuNS) dimers. For precision plasmonics, the gap distance is systematically controlled at the level of single C-C bonds via a series of alkanedithiol linkers (C