05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Additively manufactured transverse flux machine components with integrated slits for loss reduction(2022) Kresse, Thomas; Schurr, Julian; Lanz, Maximilian; Kunert, Torsten; Schmid, Martin; Parspour, Nejila; Schneider, Gerhard; Goll, DagmarLaser powder bed fusion (L-PBF) was used to produce stator half-shells of a transverse flux machine from pure iron (99.9% Fe). In order to reduce iron losses in the bulk components, radially extending slits with a nominal width of 150 and 300 µm, respectively, were integrated during manufacturing. The components were subjected to a suitable heat treatment. In addition to a microscopic examination of the slit quality, the iron losses were also measured using both a commercial and a self-developed measurement setup. The investigations showed the iron losses can be reduced by up to 49% due to the integrated slits and the heat treatment.Item Open Access Top‐down approach to study chemical and electronic properties of perovskite solar cells : sputtered depth profiling versus tapered cross‐sectional photoelectron spectroscopies(2021) Das, Chittaranjan; Zia, Waqas; Mortan, Claudiu; Hussain, Navid; Saliba, Michael; Ingo Flege, Jan; Kot, MałgorzataA study of the chemical and electronic properties of various layers across perovskite solar cell (PSC) stacks is challenging. Depth‐profiling photoemission spectroscopy can be used to study the surface, interface, and bulk properties of different layers in PSCs, which influence the overall performance of these devices. Herein, sputter depth profiling (SDP) and tapered cross‐sectional (TCS) photoelectron spectroscopies (PESs) are used to study highly efficient mixed halide PSCs. It is found that the most used SDP‐PES technique degrades the organic and deforms the inorganic materials during sputtering of the PSCs while the TCS‐PES method is less destructive and can determine the chemical and electronic properties of all layers precisely. The SDP‐PES dissociates the chemical bonding in the spiro‐MeOTAD and perovskite layer and reduces the TiO2, which causes the chemical analysis to be unreliable. The TCS‐PES revealed a band bending only at the spiro‐MeOTAD/perovskite interface of about 0.7 eV. Both the TCS and SDP‐PES show that the perovskite layer is inhomogeneous and has a higher amount of bromine at the perovskite/TiO2 interface.Item Open Access Stress-aware periodic test of interconnects(2022) Sadeghi-Kohan, Somayeh; Hellebrand, Sybille; Wunderlich, Hans-JoachimSafety-critical systems have to follow extremely high dependability requirements as specified in the standards for automotive, air, and space applications. The required high fault coverage at runtime is usually obtained by a combination of concurrent error detection or correction and periodic tests within rather short time intervals. The concurrent scheme ensures the integrity of computed results while the periodic test has to identify potential aging problems and to prevent any fault accumulation which may invalidate the concurrent error detection mechanism. Such periodic built-in self-test (BIST) schemes are already commercialized for memories and for random logic. The paper at hand extends this approach to interconnect structures. A BIST scheme is presented which targets interconnect defects before they will actually affect the system functionality at nominal speed. A BIST schedule is developed which significantly reduces aging caused by electromigration during the lifetime application of the periodic test.Item Open Access Deep learning based soft sensors for industrial machinery(2020) Maschler, Benjamin; Ganssloser, Sören; Hablizel, Andreas; Weyrich, MichaelA multitude of high quality, high-resolution data is a cornerstone of the digital services associated with Industry 4.0. However, a great fraction of industrial machinery in use today features only a bare minimum of sensors and retrofitting new ones is expensive if possible at all. Instead, already existing sensors’ data streams could be utilized to virtually ‘measure’ new parameters. In this paper, a deep learning based virtual sensor for estimating a combustion parameter on a large gas engine using only the rotational speed as input is developed and evaluated. The evaluation focusses on the influence of data preprocessing compared to network type and structure regarding the estimation quality.Item Open Access Fourier spotting : a novel setup for single-color reflectometry(2022) Siegel, Johannes; Berner, Marcel; Werner, Jürgen H.; Proll, Günther; Fechner, Peter; Schubert, MarkusSingle-color reflectrometry is a sensitive and robust detection method in optical biosensor applications, for example for bioanalysis. It is based on the interference of reflected monochromatic radiation and is label free. We present a novel setup for single-color reflectometry based on the patented technology of Berner et al. from 2016. Tilting areas of micro-mirrors allow us to encode the optical reflection signal of an analyte and reference channel into a particular carrier frequency with the amplitude being proportional to the local reflection. Therefore, a single photodiode is sufficient to collect the signals from both channels simultaneously. A 180∘ phase shift in the tilt frequency of two calibrated micro-mirror areas leads to a superposition of the analyte and reference signal which enables an efficient reduction of the baseline offset and potential baseline offset drift. A performance test reveals that we are able to detect changes of the refractive index n down to Δn < 0.01 of saline solutions as regents. A further test validates the detection of heterogeneous binding interaction. This test compromises immobilized testosterone-bovine serum albumin on a three-dimensional layer of biopolymer as ligand and monoclonal anti-testosterone antibodies as analyte. Antibody/antigen binding induces a local growth of the biolayer and change in the refractive index, which is measured via the local change of the reflection. Reproducible measurements enable for the analysis of the binding kinetics by determining the affinity constant KA = 1.59 × 10- 7 M- 1. In summary, this work shows that the concept of differential Fourier spotting as novel setup for single-color reflectometry is suitable for reliable bioanalysis.Graphical AbstractItem Open Access Ionic liquid Stabilizing high‐efficiency tin halide perovskite solar cells(2021) Li, Guixiang; Su, Zhenhuang; Li, Meng; Yang, Feng; Aldamasy, Mahmoud H.; Pascual, Jorge; Yang, Fengjiu; Liu, Hairui; Zuo, Weiwei; Di Girolamo, Diego; Iqbal, Zafar; Nasti, Giuseppe; Dallmann, André; Gao, Xingyu; Wang, Zhaokui; Saliba, Michael; Abate, AntonioTin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.Item Open Access Analyzing the influence of hyper-parameters and regularizers of topic modeling in terms of Renyi entropy(2020) Koltcov, Sergei; Ignatenko, Vera; Boukhers, Zeyd; Staab, SteffenTopic modeling is a popular technique for clustering large collections of text documents. A variety of different types of regularization is implemented in topic modeling. In this paper, we propose a novel approach for analyzing the influence of different regularization types on results of topic modeling. Based on Renyi entropy, this approach is inspired by the concepts from statistical physics, where an inferred topical structure of a collection can be considered an information statistical system residing in a non-equilibrium state. By testing our approach on four models-Probabilistic Latent Semantic Analysis (pLSA), Additive Regularization of Topic Models (BigARTM), Latent Dirichlet Allocation (LDA) with Gibbs sampling, LDA with variational inference (VLDA)-we, first of all, show that the minimum of Renyi entropy coincides with the “true” number of topics, as determined in two labelled collections. Simultaneously, we find that Hierarchical Dirichlet Process (HDP) model as a well-known approach for topic number optimization fails to detect such optimum. Next, we demonstrate that large values of the regularization coefficient in BigARTM significantly shift the minimum of entropy from the topic number optimum, which effect is not observed for hyper-parameters in LDA with Gibbs sampling. We conclude that regularization may introduce unpredictable distortions into topic models that need further research.Item Open Access Photoelectrochemical water‐splitting using CuO‐based electrodes for hydrogen production : a review(2021) Siavash Moakhar, Roozbeh; Hosseini‐Hosseinabad, Seyed Morteza; Masudy‐Panah, Saeid; Seza, Ashkan; Jalali, Mahsa; Fallah‐Arani, Hesam; Dabir, Fatemeh; Gholipour, Somayeh; Abdi, Yaser; Bagheri‐Hariri, Mohiedin; Riahi‐Noori, Nastaran; Lim, Yee‐Fun; Hagfeldt, Anders; Saliba, MichaelThe cost‐effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water‐splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO‐based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water‐splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO‐based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent‐generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.Item Open Access Characterizing the influence of charge extraction layers on the performance of triple‐cation perovskite solar cells(2023) Siekmann, Johanna; Kulkarni, Ashish; Akel, Samah; Klingebiel, Benjamin; Saliba, Michael; Rau, Uwe; Kirchartz, ThomasSelecting suitable charge transport layers and suppressing non-radiative recombination at interfaces with the absorber layer is vital for maximizing the efficiency of halide perovskite solar cells. In this study, high-quality perovskite thin films and devices are fabricated with different fullerene-based electron transport layers and different self-assembled monolayers as hole transport layers. Then, a comparative study of a significant variety of different electrical, optical, and photoemission-based characterization techniques is performed to quantify the properties of the solar cells, individual layers, and, importantly, the interfaces between them. In addition, the limitations and problems of the different measurements, the insights gained by combining different methods, and the different strategies for extracting information from the experimental raw data, are highlighted.Item Open Access Monolithically integrated GaN power stage for more sustainable 48 V DC-DC converters(2024) Basler, Michael; Mönch, Stefan; Reiner, Richard; Benkhelifa, Fouad; Quay, RüdigerIn this article, a fully monolithically integrated GaN power stage with a half-bridge, driver, level shifter, dead time and voltage mode control for 48 V DC-DC converters is proposed and analyzed. The design of the GaN IC is presented in detail, and measurements of the single function blocks and the DC–DC converter up to 48 V are shown. Finally, considerations are given on a life cycle assessment with regard to the GaN power integration. This GaN power IC or stage demonstrates a higher level of integration, resulting in a reduced bill of materials and therefore lower climate impact.