Konferenzbeiträge ab 2018

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Müller, Jens; Kaltwasser, Mahsa; Bartsch, Heike; Behrens, Arne; Handte, Thomas; Wüster, Julian; Sinzinger, Stefan
Glass and glass/LTCC interposers as heterogenous integration platform. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 7 S.

Glass as substrate or interposer material is gaining more and more interest due to its thin film compatibility and thus high-density integration capability. Multilayer stacks for processor packaging applications can be achieved by laminating Ajinomoto build-up film (ABF) on glass substrates. Some glasses exhibit very frequency stable dielectric properties and low losses which makes glass substrates also favorable for microwave applications. Moreover, in contrast to silicon as interposer material, glass materials are cheaper, they can be processed in large panel format, they do not require deposition of insulating dielectric layers and they are available with different temperature coefficients of expansion (TCE). The latter was the pre-requisite to combine glasses with TCE-matching Low Temperature Cofired Ceramic (LTCC) materials to achieve an inorganic compound substrate offering both multilayer and thin-film capability in one substrate. In addition, the glass side of the interposer might be used for integrating photonic elements and components for mixed electronic/photonic applications. Green LTCC tapes are processed in the standard sequence up to the lamination step. In parallel, holes for vias are laser drilled in the glass and filled with thick-film conductor paste. The LTCC stack is then laminated onto the glass substrate and the laminate is fired according to sintering conditions of the LTCC. During firing, the sintered LTCC establishes a strong bond to the glass without the need of an extra bonding layer. This multilayer Tape-on-Substrate approach results in zero lateral shrinkage of the LTCC and therefore high lateral dimensional accuracy. After cleaning, the glass side can be used for semi-additive or additive conductor structuring. Thick-film printing on glass as well as printing of metal-organic pastes as basis for electroplating are demonstrated. This paper summarizes the achieved results on process development and interposer substrate evaluation comprising assembly technologies and high-frequency properties.

Ortlepp, Ingo;
High-precision nanopositioning and nanomeasuring machines for alternative nanofabrication. - In: Proceedings of SPIE, Bd. 12956 (2024), 129560D, S. 129560D-1-129560D-17

For two decades, the Technische Universität Ilmenau has been developing high precision Nanopositioning and Nanomeasuring machines (NPMMs). These have proven their potential for nanometer accurate measurements in large volumes up to 200mm x 200mm x 25mm with 5 axis operation in several fields. As these machines operate according to the highest standards of metrology, offer picometer resolution and nanometer uncertainty, the goal is to transfer their unique precision to fabrication and patterning. So far, the NPMMs have been equipped with laser-based as well as tip-based patterning tools, including one photon and two photon polymerization, nanoimprint, scanning probe lithography and combinations of these technologies. The goal is basic research on these technologies, to tackle the evident challenges and explore the concealed limits to estimate the potential for later use in an industrial scale. In this paper, the specifics and advantages of the NPMMs will be described as well as the micro- and nanofabrication tools that are currently worked on. Focus is on the parameters in measurement mode and the accomplished fabrication results.

Hasieber, Michael; Rudel, Paul; Sennewald, Martin; Löhn, Torsten; Grätzel, Michael; Bergmann, Jean Pierre
Failure mechanisms of Friction stir welding tools related to process control and tool geometry. - In: Proceedings of the Institution of Mechanical Engineers, ISSN 2041-3076, Bd. 0 (2024)

Friction stir welding (FSW) is subjected to process-specific challenges including comparatively high process forces and tool wear resulting from thermomechanical stresses. As a result, the acting loads and the geometric-related tool wear can cause tool failure. The tool (shoulder) design, whether it is concave or flat, with or without geometrical elements, is mainly responsible for the related failure mechanism and tool life. Therefore, this study systematically analyzes the failure mechanisms as a function of the process temperature, during FSW of AA-6060 T66 using tools made of H13 tool steel, with different shoulder designs, namely a concave contour and a scroll contour. The mechanism responsible for tool failure was induced by repeated welding at rotational speeds of 4000 rpm and 2000 rpm, at process temperatures within the range of the secondary hardness maximum (552 ˚C and 555 ˚C) and below the temperature of the secondary hardness maximum (488 ˚C and 499 ˚C). The experimental investigation showed that reducing the rotational speed of the scrolled shoulder from 4000 rpm to 2000 rpm resulted in less wear and therefore an increase in tool life from 474 m to up to 1400 m. In this context, it has also been shown that the shoulder geometry affects the mechanism relevant to failure due to the free length of the probe.

Yigci, Ibrahim; Strohbücker, Veith; Kunze, Miles; Schatz, Markus
Measurement of the particle distribution around the tire of a light commercial vehicle on unpaved roads. - In: SAE technical papers, ISSN 2688-3627, (2024), SAE Technical Paper 2024-01-5032, S. 1-10

Dust testing of vehicles on unpaved roads is crucial in the development process for automotive manufacturers. These tests aim to ensure the functionality of locking systems in dusty conditions, minimize dust concentration inside the vehicle, and enhance customer comfort by preventing dust accumulation on the car body. Additionally, deposition on safety-critical parts, such as windshields and sensors, can pose threats to driver vision and autonomous driving capabilities. Currently, dust tests are primarily conducted experimentally at proving grounds. In order to gain early insights and reduce the need for costly physical tests, numerical simulations are becoming a promising alternative. Although simulations of vehicle contamination by dry dust have been studied in the past, they have often lacked detailed models for tire dust resuspension. In addition, few publications address the specifics of dust deposition on vehicles, especially in areas such as door gaps and locks. Many authors focus primarily on the environmental impact of vehicles due to non-exhaust emissions, such as tire and road wear particles (TRWP) and brake wear on paved roads. To close this gap, this paper presents an experimental test in which a vehicle drives through a dry dust track. Using special dust measurement techniques positioned in the wheelhouse, we determine the number and size distribution of the dust particle field around the tire circumference. The results of this experiment provide a deeper understanding of the dust dispersion patterns generated by tires on unpaved surfaces and serve as valuable data for boundary conditions and for the validation of CFD (computational fluid dynamics) simulations.

Petrich, Martin; Kletzin, Ulf
Practical fatigue strength diagrams for compression springs based on the FKM-guideline “Analytic Strength Assessment for Springs“. - In: Journal of physics, ISSN 1742-6596, Bd. 2692 (2024), 012031, S. 1-7

Today’s helical compression springs are designed according to DIN EN 13906-1. The fatigue diagrams contained there are outdated and essential influences on fatigue strength are not taken into account. In order to resolve these circumstances, endurable stresses were calculated with the FKM guideline “Analytic Strength Assessment for Springs and Spring Elements”, which was published in 2020. The application of the included safety concept results in characteristic curves for permissible stresses that are conservative with regard to real test data. Therefore, the new fatigue strength diagrams can be used directly for standard applications. This article gives an overview of the method and accompanying experiments. The presented results enable spring designers to design competitive springs in a shorter time and with less testing effort according to the current state of research.

Ved, Kalpan; Lenk, Claudia; Ivanov, Tzvetan; Hövel, Philipp; Ziegler, Martin
Bio-inspired, adaptive acoustic sensor : Sensing properties in dependence of feedback parameters. - In: AIP conference proceedings, ISSN 1551-7616, Bd. 3062 (2024), 1, 040011, S. 040011-1-040011-10

Pre-processing of the sound signal during sensing is an integral functionality of the cochlea, the part of human hearing responsible for sound sensing. This pre-pocessing, which is integrated into the sensing stage directly, enables the remarkable properties of human hearing. Similarly, integrating some of these pre-processing functionalities in technological speech processing systems strongly improves their recognition performance.We developed a bio-inspired, adaptive acoustic sensor with pre-processing capabilities like nonlinear amplification and frequency filtering functionality. The sensor is composed of a single clamped silicon beam with integrated deflection sensing and thermo-mechanical actuation, subjected to a real-time feedback. While the resonance frequency and bandwidth are determined by the geometry of the sensor beam, its transfer characteristics can be switched dynamically from linear to nonlinear regime by changing the feedback parameters. In the linear regime, the feedback controls the sensitivity and bandwidth of the sensors. Here, we elaborate on the influence of the sign of feedback strength and offset on the sensor behaviour. Changing the sign of the feedback parameters switches between amplification and damping behaviour, enabling the change of sensitivity by 44 dB. Thereby, complex oscillation modes are observed for feedback parameters with similar polarity.

Najeeb, Mussab; Schwalbe, Ulf; Herget, Mathias
Improved approach for online monitoring of second life lithium-ion batteries to optimize the performance in stationary storage systems. - In: 2023 14th International Renewable Energy Congress (IREC), (2024), insges. 6 S.

Monitoring lithium-ion batteries in their second life is of great importance when using them in stationary storage systems for grid support or in any other energy system, due to the expected different behavior and operational conditions in their second life compared to their first life. The idea of this study based on the fact that each estimation method has its advantages and drawbacks depending on the application in which the batteries will be used, and that monitoring batteries in their second life required to be integrated with the battery management system to balance cells, optimize performance, and prevent overheating. The contribution of our study can be summarized in the integration of specific methods, aiming to benefit from most of their advantages and neutralizing their drawbacks as much as possible to provide more accurate and reliable online monitoring of batteries. The combination presented in this study, consisting, for state of charge estimation, of an artificial neural network and an Unscented Kalman Filter with adjusting the filtering process using Coulomb counting, and Kalman Filter for state of health estimation, showed much better reliability and accuracy than if each method was used alone. This combination has been trained and adjusted using empirical data of second-life batteries, extracted from used electric vehicle battery bank, to obtain the best possible performance, considering the specificity of these batteries in terms of operating voltage range, lower current ratio, and other parameters.

Nycz, Julia; Link, Dietmar; Klemm, Matthias; Klee, Sascha; Haueisen, Jens
Characterization of a new fluorescence lifetime imaging ophthalmoscope. - In: Acta ophthalmologica, ISSN 1755-3768, Bd. 102 (2024), S279, insges. 1 S.

Aims/Purpose: Fluorescence lifetime imaging ophthalmoscopy (FLIO) allows in vivo measurement of autofluorescence intensity decays of endogenous fluorophores in the ocular fundus. So far, only devices from Heidelberg Engineering based on the Spectralis system have been used in FLIO research. Here, we present and characterize a new FLIO device based on the RETImap system from Roland Consult. Methods: The device is based on a confocal scanning laser ophthalmoscope (35˚ field, 512 × 512 px). A ps diode laser (BDL-SMN 473 nm, Becker & Hickl GmbH, Berlin, Germany) excites autofluorescence. The fluorescence photons are split into a short (498-560 nm, SSC) and a long (560-720 nm, LSC) spectral channel (one HPM-100-40 detector [Becker & Hickl GmbH] each) and are detected by time-correlated single photon counting (SPC-160, Becker & Hickl GmbH). We determined the maximum laser power (ILT2400, International Light Technologies, Inc. Peabody, MA, USA) and analysed the instrument's behaviour at three different laser power levels (150 μW, 200 μW and max.) in terms of laser spectrum (CAS140CT, Instrument Systems GmbH, Munich, Germany) and instrument response function (IRF). The IRF was determined using a 25 μM Eosin Y solution, mixed with a 5 M solution of potassium iodide, placed in a flat cuvette (110-OS, Hellma GmbH & Co. KG, Müllheim, Germany) in front of the objective lens of the FLIO device. Fluorescence measurements of approximately 1-min duration were performed three times for all three laser powers. The IRF and the full width at half maximum (FWHM) were calculated using FLIMX software (www.flimx.de). Results: The max. laser power was 280 μW. The peak wavelengths of the laser spectra were 467.6 (150 μW), 467.9 (200 μW) and 468.0 nm (280 μW). IRF FWHM in SSC were 298.6 ± 1.1 ps (150 μW), 341.0 ± 2.5 ps (200 μW) and 347.5 ± 6.0 ps (280 μW). In LSC, the IRF FWHM were 290.4 ± 3.8 ps (150 μW), 344.0 ± 3.4 ps (200 μW) and 358.8 ± 1.3 ps (280 μW). Results are mean ± standard deviation. Conclusions: A new fluorescence lifetime imaging ophthalmoscope has been characterized. The device offers a high laser power for fluorescence excitation, a large field of view, a high spatial resolution, and a sufficiently high time resolution. Thus, it is suitable for fluorescence lifetime studies.

Käufer, Theo; Cierpka, Christian
Volumetric Lagrangian temperature and velocity measurements with thermochromic liquid crystals. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 3, 035301, S. 1-11

We propose a Lagrangian method for simultaneous, volumetric temperature and velocity measurements. As tracer particles for both quantities, we employ encapsulated thermochromic liquid crystals (TLCs). We discuss the challenges arising from color imaging of small particles and present measurements in an equilateral hexagonal-shaped convection cell of height h = 60 mm and distance between the parallel side walls w = 10^4 mm, which corresponds to an aspect ratio Γ = 1.73. As fluid, we use a water-glycerol mixture to match the density of the TLC particles. We propose a densely-connected neural network, trained on calibration data, to predict the temperature for individual particles based on their particle image and position in the color camera images, which achieves uncertainties below 0.2 K over a temperature range of 3 K. We use Shake-the-Box to determine the 3D position and velocity of the particles and couple it with our temperature measurement approach. We validate our approach by adjusting a stable temperature stratification and comparing our measured temperatures with the theoretical results. Finally, we apply our approach to thermal convection at Rayleigh number Ra = 3.4 × 10^7 and Prandtl number Pr = 10.6. We can visualize detaching plumes in individual temperature and convective heat transfer snapshots. Furthermore, we demonstrate that our approach allows us to compute statistics of the convective heat transfer and briefly validate our results against the literature.

Girkes, Florian; Günther, M.; Rüger, Carolin; Bergmann, Jean Pierre; Töpfer-Kerst, Christian B.
An integrated approach to developing modular product families in the engineer-to-order sector. - In: Production at the leading edge of technology, (2024), S. 737-746

Nowadays, companies face challenges such as globalization, individualization and shorter product lifecycles, resulting in a constant stream of new product development processes (PDP). Modularized product families represent a powerful concept for reducing complexity and increasing resource efficiency in the PDP and beyond. Despite existing approaches and methods in the development of modular product families, there are deficits in the state of the art regarding their transfer and application to the engineer-to-order (ETO) sector, as well as for neutral indicator-based evaluation. Therefore, this paper derives a generic modularization procedure for the ETO sector and verifies it in an industrial use case. For this purpose, a heuristic swapping algorithm has been developed for grouping the components of a product family into clusters and enabling an objective mathematical evaluation. By integrating modular product structures into organizational processes, ETO manufacturers can strengthen their competitive position as well as increase their resource efficiency.