Measurement uncertainty analysis on a five-axis nano coordinate measuring machine NMM-5D following a vectorial approach :
Messunsicherheitsbetrachtungen an einem fünfachsigen Nano-Koordinatenmessgerät NMM-5D nach einem vektoriellen Ansatz. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 2, S. 61-70
Dieser Beitrag zeigt ein Konzept für eine fünfachsige Nano-Koordinatenmessmaschine zur Messung auf stark gekrümmten asphärischen und frei geformten optischen Oberflächen in einem Messvolumen von 25mm × 25mm × 5mm mit einem maximal möglichen Neigungswinkel von bis zu 60˚ zur Hochachse und einer maximalen Rotation von 360˚ um die Hochachse. Dabei wird die Probe translatorisch bewegt und der Sensor in seiner Orientierung verändert. Unter Einhaltung des Abbe-Komparatorprinzips für alle Messachsen wird die Bewegungsabweichung des Sensors bei der Rotation durch ein in-situ-Referenzmesssystem erfasst. Dieses besteht aus drei kartesisch angeordneten Fabry-Pérot-Interferometern mit dem Ursprung im Antastpunktes des Sensors, die den Abstand zu einer hemisphärischen Referenzfläche messen. Die Messunsicherheitsbetrachtung des Gesamtsystems erfolgt nach dem guide to the expression of uncertainty in measurement in einem vektoriellen Ansatz und liefert unter konservativen Annahmen eine Unsicherheit des Antastpunktes von maximal 72 nm (k=1).
https://doi.org/10.1515/teme-2020-0092
Suppression of free convection effects for spherical 1 kg mass prototype. - In: International journal of heat and mass transfer, ISSN 1879-2189, Bd. 170 (2021), 121037, insges. 13 S.
We investigate the free convection processes in the vicinity of a spherical 1 kg mass standard by two- and three-dimensional direct numerical simulations using a spectral element method. Our focus is on the determination and suppression of updraft forces in a high-precision mass comparator which are caused by temperature differences between mass standard and its environment in the millikelvin range - a source of systematic uncertainties in the high-precison mass determination. A two-dimensional model is presented first, which obtains a good agreement with previous laboratory measurements for the smaller temperature differences up to 15 mK. The influence of different boundary conditions and side lengths of the square domain is discussed for the mass standard positioned in the center of the chamber. The complexity is increased subsequently in configurations with additional built-ins for counter heating in form of planar plates or hemispherical shells above the mass standard. The latter ones lead to a full compensation of the updraft force. Three-dimensional simulations in a closed cubic chamber confirm the two-dimensional findings and additionally reveal complex secondary flow patterns in the vicinity of the mass standard. The reduction of the heat transfer due to the built-ins is also demonstrated by a comparison of the Nusselt numbers as a function of the Rayleigh number in the chosen parameter range. Our simulations suggest that such additional constructive measures can enhance the precision of the mass determination by suppression of free convection and related systematic uncertainties.
https://doi.org/10.1016/j.ijheatmasstransfer.2021.121037
Functionalized three-dimensional multilayer ceramic modules. - In: Electronics, ISSN 2079-9292, Bd. 10 (2021), 3, 248, insges. 11 S.
Three-dimensional interconnect devices are still strongly related to plastic materials. Since the use of these materials is limited in harsh environments, there is an application gap, which could be filled by ceramic circuit carriers. Low-temperature cofired ceramics (LTCC) offer promising solutions to fill this gap. This work provides a feasibility study, including the whole technological chain of ceramic multilayer processing. Targeting a curved multilayer substrate, fully equipped with SMD (Surface-mounted device) components, the particularities of single process steps are investigated. Two shaping methods based on quartz glass molds are compared with regard to shape fidelity and technological effort. The investigation of internal conductor lines and via connections reveals that the metallization should have a minimum width of 200 m and the via diameter is limited to 150 m. Further considerations focus on the possible footprint of components and use of cavities to increase the footprint of components. The limits of wire bonding on curved surfaces were inspected. Finally, the work presents a demonstrator of a fully equipped four-layer ceramic circuit, including internal wiring. Hence, the transfer of the 2.5-dimensional multilayer ceramic technology into the third dimension is proven.
https://doi.org/10.3390/electronics10030248
A method to approach constant isotropic permeabilities and demagnetization factors of magneto-rheological elastomers. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 527 (2021), 167742
The use of non-conventional materials is nowadays of much interest in scientific community. Magneto-rheological elastomers are hybrid materials, which in presence of magnetic fields state a change in their mechanical properties. They are composed by an elastomeric matrix with embedded magnetic particles. One of the most attractive features of these materials is that as soon as the magnetic field is removed from the material, the original mechanical properties are completely recovered, with negligible differences in comparison to the original state. This paper focuses on the study of magnetic characteristics of these smart materials, such as relative permeability and demagnetizing factors, for samples with different volume concentration of ferromagnetic particles.
https://doi.org/10.1016/j.jmmm.2021.167742
The impact of individual electrical fields and anatomical factors on the neurophysiological outcomes of tDCS: a TMS-MEP and MRI study. - In: Brain stimulation, ISSN 1876-4754, Bd. 14 (2021), 2, S. 316-326
Background - Transcranial direct current stimulation (tDCS), a neuromodulatory non-invasive brain stimulation technique, has shown promising results in basic and clinical studies. The known interindividual variability of the effects, however, limits the efficacy of the technique. Recently we reported neurophysiological effects of tDCS applied over the primary motor cortex at the group level, based on data from twenty-nine participants who received 15min of either sham, 0.5, 1.0, 1.5 or 2.0 mA anodal, or cathodal tDCS. The neurophysiological effects were evaluated via changes in: 1) transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP), and 2) cerebral blood flow (CBF) measured by functional magnetic resonance imaging (MRI) via arterial spin labeling (ASL). At the group level, dose-dependent effects of the intervention were obtained, which however displayed interindividual variability. - Method - In the present study, we investigated the cause of the observed inter-individual variability. To this end, for each participant, a MRI-based realistic head model was designed to 1) calculate anatomical factors and 2) simulate the tDCS- and TMS-induced electrical fields (EFs). We first investigated at the regional level which individual anatomical factors explained the simulated EFs (magnitude and normal component). Then, we explored which specific anatomical and/or EF factors predicted the neurophysiological outcomes of tDCS. - Results - The results highlight a significant negative correlation between regional electrode-to-cortex distance (rECD) as well as regional CSF (rCSF) thickness, and the individual EF characteristics. In addition, while both rCSF thickness and rECD anticorrelated with tDCS-induced physiological changes, EFs positively correlated with the effects. - Conclusion - These results provide novel insights into the dependency of the neuromodulatory effects of tDCS on individual physical factors.
https://doi.org/10.1016/j.brs.2021.01.016
Field-cycling NMR and DNP - a friendship with benefits. - In: Journal of magnetic resonance, ISSN 1096-0856, Bd. 322 (2021), 106851, S. 1-16
Field-cycling relaxometry, or rather its electronic version with a resistive magnet which requires signal detection at a field strength of 1 Tesla or below, remains an inherently insensitive technique due to the construction compromise that goes along with the need for a fast-switching, low-inductance magnet. For the same reasons, signal lifetime is short and frequency resolution is typically not given, at least for the predominantly used hydrogen nuclei. Dynamic Nuclear Polarization (DNP) bears the potential to circumvent these disadvantages: not only has it been demonstrated to enhance magnetization by up to three orders of magnitude beyond its thermal value, but it also provides the possibility to address particular parts of a molecule, thus generating selectivity even in the absence of spectral resolution. At the same time, DNP requires the introduction of stable radicals giving rise to additional relaxation contributions. This article presents a straightforward way to recover the native relaxation rates of the undisturbed system, and shows examples in different research fields where field-cycling relaxometry is traditionally used for refining models of molecular dynamics and interactions.
https://doi.org/10.1016/j.jmr.2020.106851
Numerical modeling of an inductively coupled plasma torch using OpenFOAM. - In: Computers & fluids, Bd. 216 (2021), 104807
A customized code using the free and fully open-source CFD software package OpenFOAM was developed to simulate a two-dimensional axisymmetric model of an inductively coupled plasma torch. To efficiently calculate the high-frequency magnetic fields generated by the inductive coil, a technique based on the vector potential formulation of Maxwell's equations was implemented using the block coupled matrix solver provided by the foam-extend toolbox. While the fluid equations for the inner torch region are solved under the assumption of a laminar flowing argon plasma under atmospheric pressure and local thermodynamic equilibrium conditions, the electromagnetic equations are solved on an overlapping mesh extended far outside the torch. Moreover, a novel technique for initializing the plasma solver by separately precomputing the velocity and temperature fields is presented. Using this approach our plasma solver can run in both steady-state and transient modes. The implementation has been validated by means of analytical methods, and the simulation results of the Tekna-PL50 plasma torch have been compared against literature data. The results obtained using the OpenFOAM code are in good agreement with those of the commercial CFD codes.
https://doi.org/10.1016/j.compfluid.2020.104807
Low-temperature co-fired ceramic-based thermoelectric generator with cylindrical grooves for harvesting waste heat from power circuits. - In: Applied thermal engineering, ISSN 1359-4311, Bd. 184 (2021), 116367
https://doi.org/10.1016/j.applthermaleng.2020.116367
Photo-thermoelectric conversion using black silicon with enhanced light trapping performance far beyond the band edge absorption. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 1, S. 1818-1826
https://doi.org/10.1021/acsami.0c17279
Pulsed optically pumped magnetometers: addressing dead time and bandwidth for the unshielded magnetorelaxometry of magnetic nanoparticles. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 4, 1212, insges. 19 S.
https://doi.org/10.3390/s21041212