Influence of contact pressure on the specific electrical contact resistance of copper. - In: IEEE transactions on components, packaging and manufacturing technology, ISSN 2156-3985, Bd. 12 (2022), 6, S. 973-980
The specific electrical contact resistance (SECR) [ Ωm2 ] of Cu-ETP (CW004A) contacts is characterized in dependence of contact pressure up to high pressures close to the tensile strength of the base material. Two different material states are considered, R200 (soft) and R300. Static four-wire measurements are carried out on a special experimental setup, which favors homogeneous contact states during mechanical loading. A finite-element simulation is utilized for interpretation and evaluation of the measurements, including the deformation of the samples during the test. The results show that the SECR of the harder material state R300 is higher than that of the softer material R200. The developed data show a decrease of SECR with increasing contact pressure. For contact pressures up to 0.5 of the tensile strength σt of the base material, the SECR decreases according to a power law. For contact pressures above 0.6 σt , the decrease shifts toward a linear behavior. In addition, the measurements show that the SECR vanishes at contact pressures in region of the tensile strength of the base material.
https://doi.org/10.1109/TCPMT.2022.3176740
Six decades of research on 2D materials: progress, dead ends, and new horizons. - In: IEEE journal of the Electron Devices Society, ISSN 2168-6734, Bd. 10 (2022), S. 443-451
The present paper guides the reader through six decades of research on 2D materials, thereby putting special focus on the use of these materials for electronic devices. It is shown that after a slow start and only little activity over many years, since 2004 the exploration of 2D materials advanced at an enormous pace. While some of the high expectations raised in the so-called golden era of graphene did not fulfil, other electronic applications for 2D materials that originally were not on the agenda gain increasing attention now. One of the main research topics in the field of 2D materials during the early 2000s was high-performance graphene transistors. This effort, however, led to a dead end due the consequences of the missing bandgap in graphene. On the other hand, the semiconducting 2D materials show potential for different device concepts including stacked-channel 2D nanosheet MOSFETs and 2D memristors. The former may become the transistor architecture of choice at the end of the CMOS roadmap and 2D memristors represent a promising device concept for future neuromorphic computing, a type of information processing that shows great potential for artificial intelligence applications where energy efficiency is a key requirement.
https://doi.org/10.1109/JEDS.2022.3144500
Numerical simulation of the deformation behavior of softwood tracheids for the calculation of the mechanical properties of wood-polymer composites. - In: Polymers, ISSN 2073-4360, Bd. 14 (2022), 13, 2574, insges. 25 S.
From a fiber composite point of view, an elongated softwood particle is a composite consisting of several thousand tracheids, which can be described as fiber wound hollow profiles. By knowing their deformation behavior, the deformation behavior of the wood particle can be described. Therefore, a numerical approach for RVE- and FEM-based modelling of the radial and tangential compression behavior of pine wood tracheids under room climate environment is presented and validated with optical and laser-optical image analysis as well as tensile and compression tests on pine sapwood veneer strips. According to the findings, at 23 ˚C and 12% moisture content, at least 10 MPa must be applied for maximum compaction of the earlywood tracheids. The latewood tracheids can withstand at least 100 MPa compression pressure and would deform elastically at this load by about 20%. The developed model can be adapted for other wood species and climatic conditions by adjusting the mechanical properties of the base materials of the cell wall single layers (cellulose, hemicellulose, lignin), the dimensions and the structure of the vessel elements, respectively.
https://doi.org/10.3390/polym14132574
Microtoxicology by microfluidic instrumentation: a review. - In: Lab on a chip, ISSN 1473-0189, Bd. 22 (2022), 14, S. 2600-2623
Microtoxicology is concerned with the toxic effects of small amounts of substances. This review paper discusses the application of small amounts of noxious substances for toxicological investigation in small volumes. The vigorous development of miniaturized methods in microfluidics over the last two decades involves chip-based devices, micro droplet-based procedures, and the use of micro-segmented flow for microtoxicological studies. The studies have shown that the microfluidic approach is particularly valuable for highly parallelized and combinatorial dose-response screenings. Accurate dosing and mixing of effector substances in large numbers of microcompartments supplies detailed data of dose-response functions by highly concentration-resolved assays and allows evaluation of stochastic responses in case of small separated cell ensembles and single cell experiments. The investigations demonstrate that very different biological targets can be studied using miniaturized approaches, among them bacteria, eukaryotic microorganisms, cell cultures from tissues of multicellular organisms, stem cells, and early embryonic states. Cultivation and effector exposure tests can be performed in small volumes over weeks and months, confirming that the microfluicial strategy is also applicable for slow-growing organisms. Here, the state of the art of miniaturized toxicology, particularly for studying antibiotic susceptibility, drug toxicity testing in the miniaturized system like organ-on-chip, environmental toxicology, and the characterization of combinatorial effects by two and multi-dimensional screenings, is discussed. Additionally, this review points out the practical limitations of the microtoxicology platform and discusses perspectives on future opportunities and challenges.
https://doi.org/10.1039/D2LC00268J
Review: a survey on configurations and performance of flow-mode MR valves. - In: Applied Sciences, ISSN 2076-3417, Bd. 12 (2022), 12, 6260, S. 1-22
Magnetorheological (MR) actuators are semi-active devices controlled by magnetic stimuli. The technology has been commercialized in the automotive industry or high-quality optical finishing applications. It harnesses the rheology of smart fluids to result in the unique application of the material. By a wide margin, the most common example of an MR actuator is a flow-mode single-tube housing with a control valve (electromagnet with a fixed-size air gap filled with the MR fluid) operating in a semi-active vibration control environment. The analysis of the prior art shows that the developed configurations of MR valves vary in size, complexity, the ability to generate adequate levels of pressure, and the interactions with the MR fluid’s rheology resulting in various performance envelopes. Moreover, miscellaneous testing procedures make a direct valve-to-valve comparison difficult. Therefore, in this paper we present a detailed and systematic review of MR control valves, provide classification criteria, highlight the operating principle, and then attempt to categorize the valves into groups sharing similarities in the design and performance envelope(s). Moreover, a simple performance metric based on the shear stress calculation is proposed, too, for evaluating the performance of particular valving prototypes. In the review, we discuss the key configurations, highlight their strengths and weaknesses and explore various opportunities for tuning their performance range. The review provides complementary information for the engineers and researchers with a keen interest in MR applications, in general. It is an organized and and critical study targeted at improvements in the categorization and description of MR devices.
https://doi.org/10.3390/app12126260
State of charge and state of health assessment of viologens in aqueous-organic redox-flow electrolytes using in situ IR spectroscopy and multivariate curve resolution. - In: Advanced science, ISSN 2198-3844, Bd. 9 (2022), 17, 2200535, S. 1-10
Aqueous-organic redox flow batteries (RFBs) have gained considerable interest in recent years, given their potential for an economically viable energy storage at large scale. This, however, strongly depends on both the robustness of the underlying electrolyte chemistry against molecular decomposition reactions as well as the device's operation. With regard to this, the presented study focuses on the use of in situ IR spectroscopy in combination with a multivariate curve resolution approach to gain insight into both the molecular structures of the active materials present within the electrolyte as well as crucial electrolyte state parameters, represented by the electrolyte's state of charge (SOC) and state of health (SOH). To demonstrate the general applicability of the approach, methyl viologen (MV) and bis(3-trimethylammonium)propyl viologen (BTMAPV) are chosen, as viologens are frequently used as negolytes in aqueous-organic RFBs. The study's findings highlight the impact of in situ spectroscopy and spectral deconvolution tools on the precision of the obtainable SOC and SOH values. Furthermore, the study indicates the occurrence of multiple viologen dimers, which possibly influence the electrolyte lifetime and charging characteristics.
https://doi.org/10.1002/advs.202200535
Tuning of high-temperature dielectric properties in the system (Bi0.5Na0.5)TiO3-BaTiO3-CaZrO3. - In: Ceramics international, ISSN 1873-3956, Bd. 48 (2022), 15, S. 22228-22236
Solid solutions of the (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xCaZrO3 system are regarded as promising dielectrics for high-temperature capacitors as they exhibit a remarkable flat trend of the permittivity over a large temperature range coupled with comparable low dielectric losses. In this work, the composition 0.8(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.2CaZrO3 was chosen in an attempt to optimize especially the high-temperature dielectric properties above 200 ˚C. In particular, the influence of excess bismuth to account for element losses caused by evaporation, and the effect of manganese as acceptor dopant are reported. Conventional solid-state reaction route was used to synthesize selected compositions. X-ray diffraction was used to confirm a pseudo-cubic perovskite main phase in all examined compositions, although small traces of a zirconia secondary phase were also detected. All samples exhibit an expected flat trend of the relative permittivity with a maximum deviation of the permittivity lower than 15% between -80 ˚C and 300 ˚C. The unmodified base composition shows small dielectric loss (<2%) between -55 ˚C and 265 ˚C. By using small quantities of manganese doping, the small-loss temperature range was extended (-70 ˚C and 300 ˚C). Excess bismuth also affects the temperature-dependent dielectric losses, resulting in a narrowed temperature range, eventually limiting the application possibilities.
https://doi.org/10.1016/j.ceramint.2022.04.220
THz broadband channel sounders. - In: THz Communications, (2022), S. 37-48
This chapter is the perfect introduction to get an overview of THz channel sounder technologies. Additionally, all relevant state of the art and references for the field of THz channel sounding are summarized. The aim of the THz sounder chapter is to create a basic understanding of measurement setups and challenges for the measurement of the electromagnetic wave propagation in the THz range. All necessary principles, from generating the transmit signal over different mixing principles to the THz band and the data acquisition, are compact summarized.
Designing MoS2 channel properties for analog memory in neuromorphic applications. - In: Journal of vacuum science & technology, ISSN 2166-2754, Bd. 40 (2022), 3, S. 030602-1-030602-5
In this paper, we introduce analog nonvolatile random access memory cells for neuromorphic computing. The analog memory cell MoS2 channel is designed based on the simulation model including Fowler-Nordheim tunneling through a charge-trapping stack, trapping process, and transfer characteristics to describe a full write/read circle. 2D channel materials provide scaling to higher densities as well as preeminent modulation of the conductance by the accumulated space charge from the oxide trapping layer. In this paper, the main parameters affecting the distribution of memory states and their total number are considered. The dependence of memory state distribution on channel doping concentration and the number of layers is given. In addition, how the nonlinearity of memory state distribution can be overcome by variation of operating conditions and by applying pulse width modulation to the bottom gate voltage is also shown.
https://doi.org/10.1116/6.0001815
Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 1. Measurement of strain. - In: Smart materials and structures, ISSN 1361-665X, Bd. 31 (2022), 7, 075014, S. 1-13
https://doi.org/10.1088/1361-665X/ac736d