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- ItemOrigami-Inspired Shape Memory Folding Microactuator(Basel : MDPI, 2020) Seigner, Lena; Bezsmertna, Olha; Fähler, Sebastian; Tshikwand, Georgino; Wendler, Frank; Kohl, ManfredThis paper presents the design, fabrication and performance of origami-based folding microactuators based on a cold-rolled NiTi foil of 20 µm thickness showing the one-way shape memory effect. Origami refers to a variety of techniques of transforming planar sheets into three-dimensional (3D) structures by folding, which has been introduced in science and engineering for, e.g., assembly and robotics. Here, NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a set of predetermined 3D shapes upon heating. While this concept has been demonstrated at the macro scale, we intend to transfer this concept into microtechnology by combining state-of-the art methods of micromachining. NiTi foils are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. A thermo-mechanical treatment is used for shape setting of as-received specimens to reach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. The achieved results are an important step towards the development of cooperative multistable microactuator systems for 3D self-assembly.
- ItemPulsed laser deposition of thick BaHfO3-doped YBa 2Cu307-δ films on highly alloyed textured Ni-W tapes(Bristol : Institute of Physics Publishing, 2014) Sieger, M.; Hänisch, J.; Iida, K.; Gaitzsch, U.; Rodig, C.; Schultz, L.; Holzapfel, B.; Hühne, R.YBa2Cu3O7-δ (YBCO) films with a thickness of up to 3 μm containing nano-sized BaHfO3 (BHO) have been grown on Y2O3/Y-stabilized ZrO2/CeO 2 buffered Ni-9at% W tapes by pulsed laser deposition (PLD). Structural characterization by means of X-ray diffraction confirmed that the YBCO layer grew epitaxial. A superconducting transition temperature T c of about 89 K with a transition width of 1 K was determined, decreasing with increasing BHO content. Critical current density in self-field and at 0.3 T increased with increasing dopant level.
- ItemFemtosecond spectroscopy in a nearly optimally doped Fe-based superconductors FeSe0.5Te0.5 and Ba(Fe 1-xCox)2As2/Fe thin film(Bristol : Institute of Physics Publishing, 2014) Bonavolontà, C.; Parlato, L.; De, Lisio, C.; Valentino, M.; Pepe, G.P.; Kazumasa, I.; Kurth, F.; Bellingeri, E.; Pallecchi, I.; Putti, M.; Ferdeghini, C.; Ummarino, G.A.; Laviano, F.Femtosecond spectroscopy has been used to investigate the quasi-particle relaxation times in nearly optimally doped Fe-based superconductors FeSe 0.5Te0.5 and optimally doped Ba-122 thin films growth on a Fe buffer layer. Experimental results concerning the temperature dependence of the relaxation time of such pnictides both in the superconducting state are now presented and discussed. Modelling the T-dependence of relaxation times an estimation of both electron-phonon constant and superconducting energy gap in the excitation spectrum of both Fe(Se,Te) and Ba-122 compounds is obtained.
- ItemMeasurements of Streams Agitated by Fluid Loaded SAW-devices Using a Volumetric 3-component Measurement Technique (V3V)(Amsterdam [u.a.] : Elsevier, 2015) Kiebert, Florian; König, Jörg; Kykal, Carsten; Schmidt, HagenUtilizing surface acoustic waves (SAW) to induce tailored fluid motion via the acoustic streaming requires detailed knowledge about the acoustic bulk wave excitation. For the first time, the Defocus Digital Particle Image Velocimetry is used to measure the fluid motion originating from a fluid loaded SAW-device. With this flow measurement technique, the acoustic streaming-induced fluid motion can be observed volumetrically, which is attractive not only for application, but also for simulation in order to gain deeper insights regarding three-dimensional acoustic effects.
- ItemVisualization of Bulk Magnetic Properties by Neutron Grating Interferometry(Amsterdam [u.a.] : Elsevier, 2015) Betz, B.; Rauscher, P.; Siebert, R.; Schaefer, R.; Kaestner, A.; Van Swygenhoven, H.; Lehmann, E.; Grünzweig, C.The neutron Grating Interferometer (nGI) is a standard user instrument at the cold neutron imaging beamline ICON (Kaestner, 2011) at the neutron source SINQ at Paul Scherrer Institute (PSI), Switzerland. The setup is able to deliver simultaneously information about the attenuation, phase shift (DPC) (Pfeiffer, 2006) and scattering properties in the so-called dark-field image (DFI) (Grünzweig, 2008-I) of a sample. Since neutrons only interact with the nucleus they are often able to penetrate deeper into matter than X-rays, in particular heavier materials. A further advantage of neutrons compared to X-rays is the interaction of the neutron's magnetic moment with magnetic structures that allows for the bulk investigation of magnetic domain structures using the nGI technique (Grünzweig, 2008-II). The nGI-setup and its technique for imaging with cold neutrons is presented in this contribution. The main focus will be on magnetic investigations of electrical steel laminations using the nGI technique. Both, grain-oriented (GO) and non-oriented (NO) laminations will be presented. GO-laminations are widely used in industrial transformer applications, while NO-sheets are common in electrical machines. For grain-oriented sheet, domain walls were visualized individually,spatially resolved, while in NO-sheet a relative density distribution is depicted.
- ItemJosephson and tunneling junctions with thin films of iron based superconductors(Amsterdam [u.a.] : Elsevier, 2012) Schmidt, S.; Döring, S.; Tympel, V.; Schmidl, F.; Haindl, S.; Iida, K.; Holzapfel, B.; Seidel, P.We produced planar hybrid Superconductor - Normal metal - Superconductor (SNS') junctions and interfaceengineered edge junctions (SN'S' or SIS' with normal metal (N') or insulating (I) barrier) with various areas using Co-doped Ba-122 as base electrode. Varying the thickness of the Normal metal (gold) barrier of the planar junctions, we can either observe Josephson behavior at thinner gold thicknesses or transport dominated by Andreev reflection. The edge junctions seem to form a SN'S'-contact.
- ItemBaFe2As2/Fe bilayers with [001]-tilt grain boundary on MgO and SrTiO3 bicrystal substrates(Amsterdam [u.a.] : Elsevier, 2013) Iida, K.; Haindl, S.; Kurth, F.; Hänisch, J.; Schulz, L.; Holzapfel, B.Co-doped BaFe2As2 (Ba-122) can be realized on both MgO and SrTiO3 bicrystal substrates with [001]-tilt grain boundary by employing Fe buffer layers. However, an additional spinel (i.e. MgAl 2O4) buffer between Fe and SrTiO3 is necessary since an epitaxial, smooth surface of Fe layer can not be grown on bare SrTiO3. Both types of bicrystal films show good crystalline quality.
- ItemThree-Dimensional Imaging of Magnetic Domains with Neutron Grating Interferometry(Amsterdam [u.a.] : Elsevier, 2015) Manke, I.; Kardjilov, N.; Schäfer, R.; Hilger, A.; Grothausmann, R.; Strobl, M.; Dawson, M.; Grünzweig, Ch.; Tötzke, Ch.; David, Ch.; Kupsch, A.; Lange, A.; Hentschel, M.P.; Banhart, J.This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique.
- ItemDetermination of Bulk Magnetic Volume Properties by Neutron Dark-Field Imaging(Amsterdam [u.a.] : Elsevier, 2015) Grünzweig, Christian; Siebert, René; Betz, Benedikt; Rauscher, Peter; Schäfer, Rudolf; Lehmann, EberhardFor the production of high-class electrical steel grades a deeper understanding of the magnetic domain interaction with induced mechanical stresses is strongly required. This holds for non-oriented (NO) as well as grain-oriented (GO) steels. In the case of non-oriented steels the magnetic property degeneration after punching or laser cutting is essential for selecting correct obstructing material grades and designing efficient electrical machines. Until now these effects stay undiscovered due to the lack of adequate investigation methods that reveal local bulk information on processed laminations. Here we show how the use of a non-destructive testing method based on a neutron grating interferometry providing the dark-field image contrast delivers spatially-resolved transmission information about the local bulk domain arrangement and domain wall density. With the help of this technique it is possible to visualize magnetization processes within the NO laminations. Different representative manufacturing techniques are compared in terms of magnetic flux density deterioration such as punching, mechanically cutting by guillotine as well as laser fusion cutting using industrial high power laser beam sources. For GO steel laminations the method is applicable on the one hand to visualize the internal domain structure without being hindered by the coating layer. On the other hand, we can show the influence of the coating layer onto the underlying domain structure.
- ItemCombinatorial synthesis of (YxGd1-x)Ba2Cu3Ox superconducting thin films(Amsterdam [u.a.] : Elsevier, 2012) Kirchner, A.; Erbe, M.; Freudenberg, T.; Hühne, R.; Feys, J.; Van Driessche, I.; Schultz, L.; Holzapfel, B.Environmentally friendly water-based YBa2Cu3Ox (YBCO) and GdBa2Cu3Ox (GdBCO) precursor solutions were synthesized to realize thin films by chemical solution deposition. Pure YBCO and GdBCO precursor solutions were used for ink plotting on SrTiO3 substrates and subsequent thermal treatment at the corresponding crystallization temperature. Phase formation of Gd123 requires a higher crystallization temperature of 840 °C compared to the Y123 phase. The critical temperature of YBCO films is about 92 K with a sharp transition into the superconducting state. Micro liter sized ink volumes of YBCO and GdBCO were successfully mixed for two-dimensional ink plotting of a (YxGd1-x)Ba2Cu3Ox film library. A homogeneous surface and no indication of a-axis growth were found in all mixed films.