TY - JOUR A1 - Stajanca, Pavol A1 - Topolniak, Ievgeniia A1 - Pötschke, Samuel A1 - Krebber, Katerina T1 - Solution-mediated cladding doping of commercial polymer optical fibers N2 - Solution doping of commercial polymethyl methacrylate (PMMA) polymer optical fibers (POFs) is presented as a novel approach for preparation of custom cladding-doped POFs (CD-POFs). The presented method is based on a solution-mediated diffusion of dopant molecules into the fiber cladding upon soaking of POFs in a methanol-dopant solution. The method was tested on three different commercial POFs using Rhodamine B as a fluorescent dopant. The dynamics of the diffusion process was studied in order to optimize the doping procedure in terms of selection of the most suitable POF, doping time and conditions. Using the optimized procedure, longer segment of fluorescent CD-POF was prepared and its performance was characterized. Fiber’s potential for sensing and illumination applications was demonstrated and discussed. The proposed method represents a simple and cheap way for fabrication of custom, short to medium length CD-POFs with various dopants. KW - Polymer optical fiber KW - Solution doping KW - Polymethyl methacrylate KW - Rhodamine B KW - Dye-doped fiber KW - Fluorescent optical fiber PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-441045 DO - https://doi.org/10.1016/j.yofte.2018.02.008 SN - 1068-5200 SN - 1095-9912 VL - 41 SP - 227 EP - 234 PB - Elsevier Inc. AN - OPUS4-44104 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stajanca, Pavol A1 - Mihai, L. A1 - Sporea, D. A1 - Negut, D. A1 - Sturm, Heinz A1 - Schukar, Marcus A1 - Krebber, Katerina ED - Webb, D. J. ED - Scully, P. ED - Sugden, K. T1 - Impacts of gamma irradiation on cytop plastic optical fibres N2 - Impact of gamma radiation on transmission of a commercial Cytop polymer optical fibre (Lucina, Asahi Glass Company) is investigated. Spectral dependence of radiation induced attenuation in the investigated fibre is measured in the VIS-NIR spectral region. Besides attenuation increase, radiation is found to increase fibre susceptibility to water as well. While pristine Cytop fibre is rather humidity insensitive, strong humidity related absorption in the NIR region is observed after fibre irradiation. Selective irradiation of separate fibre sections is proposed as a way of fibre humidity sensitization and quasi-distributed water detection is demonstrated using optical time domain reflectometry at 1310 nm. T2 - POF 2016: 25th International Conference on Plastic Optical Fibres CY - Birmingham, UK DA - 13.09.2016 KW - Polymer optical fibers KW - Cytop KW - Gamma radiation PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-403216 SN - 9781854494085 SP - 114 EP - 117 CY - Birmingham AN - OPUS4-40321 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hirsch, Philipp Daniel A1 - Kunji Purayil, Sruthi Krishna A1 - Lecompagnon, Julien A1 - Hassenstein, Christian A1 - Ziegler, Mathias T1 - Robotergestützte 3D-Scans und Laserthermografie zur Prüfung an komplexen Bauteilen auf Risse N2 - Die Integration von Automation und Robotik in die Prüfprozesse ermöglicht die Untersuchung komplexer Bauteile. Diese Studie präsentiert die robotergestützte Laserthermografie, um Risse in solchen Bauteilen zu identifizieren und analysieren. Diese Technik ermöglicht die automatisierte Rissprüfung welche im Vergleich zur Farbeindringprüfung auf viele, meist manuelle, Arbeitsschritte sowie die notwendigen Chemikalien verzichtet. Zusätzlich wird ein automatisiertes Einscannen der Bauteile mithilfe eines Linienscanners vorgestellt. Dieser Schritt ermöglicht eine detaillierte 3D-Rekonstruktion der Bauteilgeometrie und ermöglicht eine einfache Korrektur von Abweichungen in der Bauteilaufnahme und eröffnet Möglichkeiten zur adaptiven Bahnplanung bei Bauteilverformungen. Die Rückprojektion der gefundenen Risse auf die Oberfläche des Bauteils kann automatisiert erfolgen. Dieser Schritt erlaubt nicht nur die Identifikation der Risse, sondern auch eine genauere Analyse ihrer Geometrie und Lage am Bauteil. Die Kombination von robotergestützter Laserthermografie, automatisiertem 3DScanning und Rückprojektion der Risse auf die Bauteiloberfläche eröffnet neue Möglichkeiten in der zerstörungsfreien Prüfung von komplexen Bauteilen und erweitert damit mögliche Anwendungsfelder. T2 - Jahrestagung der Deutschen Gesellschaft für Zerstörungsfreie Prüfung (DGZfP) 2024 CY - Osnabrück, Germany DA - 06.05.2024 KW - ZFP4.0 KW - Automatisierung KW - Thermografie KW - Laser KW - Roboter PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-604811 UR - https://www.ndt.net/?id=29520 VL - 182 SP - 1 EP - 8 PB - NDT.net AN - OPUS4-60481 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hauffen, J. C. A1 - Kästner, L. A1 - Ahmadi, Samim A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Learned block iterative shrinkage thresholding algorithm for photothermal super resolution imaging N2 - Block-sparse regularization is already well known in active thermal imaging and is used for multiple-measurement-based inverse problems. The main bottleneck of this method is the choice of regularization parameters which differs for each experiment. We show the benefits of using a learned block iterative shrinkage thresholding algorithm (LBISTA) that is able to learn the choice of regularization parameters, without the need to manually select them. In addition, LBISTA enables the determination of a suitable weight matrix to solve the underlying inverse problem. Therefore, in this paper we present LBISTA and compare it with state-of-the-art block iterative shrinkage thresholding using synthetically generated and experimental test data from active thermography for defect reconstruction. Our results show that the use of the learned block-sparse optimization approach provides smaller normalized mean square errors for a small fixed number of iterations. Thus, this allows us to improve the convergence speed and only needs a few iterations to generate accurate defect reconstruction in photothermal super-resolution imaging. KW - Thermography KW - Laser KW - Machine learning KW - Optimization KW - Non-destructive testing KW - NDT KW - Neural network KW - Defect reconstruction KW - Block-sparsity KW - Active thermal imaging KW - Regularization KW - Laser thermography PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-554598 DO - https://doi.org/10.3390/s22155533 SN - 1424-8220 VL - 22 IS - 15 SP - 1 EP - 15 PB - MDPI CY - Basel AN - OPUS4-55459 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Super resolution laser line scanning thermography N2 - In this paper we propose super resolution measurement and post-processing strategies that can be applied in thermography using laser line scanning. The implementation of these techniques facilitates the separation of two closely spaced defects and avoids the expected deterioration of spatial resolution due to heat diffusion. The experimental studies were performed using a high-power laser as heat source in combination with pulsed thermography measurements (step scanning) or with continuous heating measurements (continuous scanning). Our work shows that laser line step scanning as well as continuous scanning both can be used within our developed super resolution (SR) techniques. Our SR techniques make use of a compressed sensing based algorithm in post- processing, the so-called iterative joint sparsity (IJOSP) approach. The IJOSP method benefits from both - the sparse nature of defects in space as well as from the similarity of each measurement. In addition, we show further methods to improve the reconstruction quality e.g. by simple manipulations in thermal image processing such as by considering the effect of the scanning motion or by using different optimization algorithms within the IJOSP approach. These super resolution image processing methods are discussed so that the advantages and disadvantages of each method can be extracted. Our contribution thus provides new approaches for the implementation of super resolution techniques in laser line scanning thermography and informs about which experimental and post-processing parameters should be chosen to better separate two closely spaced defects. KW - Super resolution KW - Laser thermography KW - Compressed sensing KW - Laser scanning KW - Joint sparsity PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509796 DO - https://doi.org/10.1016/j.optlaseng.2020.106279 SN - 0143-8166 VL - 134 SP - 106279 PB - Elsevier Ltd. AN - OPUS4-50979 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pauw, Brian Richard A1 - Smith, A. J. A1 - Snow, T. A1 - Shebanova, O. A1 - Sutter, J. P. A1 - Ilavsky, J. A1 - Hermida-Merino, D. A1 - Smales, Glen Jacob A1 - Terrill, N. J. A1 - Thünemann, Andreas A1 - Bras, W. T1 - Extending synchrotron SAXS instrument ranges through addition of a portable, inexpensive USAXS module with vertical rotation axes N2 - Ultra-SAXS can enhance the capabilities of existing synchrotron SAXS/WAXS beamlines. A compact ultra-SAXS module has been developed, which extends the measurable q-range with 0.0015 ≤ q (nm−1) ≤ 0.2, allowing structural dimensions in the range 30 ≤ D (nm) ≤ 4000 to be probed in addition to the range covered by a high-end SAXS/WAXS instrument. By shifting the module components in and out on their respective motor stages, SAXS/WAXS measurements can be easily and rapidly interleaved with USAXS measurements. The use of vertical crystal rotation axes (horizontal diffraction) greatly simplifies the construction, at minimal cost to efficiency. In this paper, the design considerations, realization and synchrotron findings are presented. Measurements of silica spheres, an alumina membrane, and a porous carbon catalyst are provided as application examples. KW - X-ray scattering KW - Microstructure KW - Instrumentation KW - SAXS KW - USAXS KW - Nanostructure KW - Combined techniques PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-524919 DO - https://doi.org/10.1107/S1600577521003313 SN - 1600-5775 VL - 28 IS - 3 SP - 824 EP - 833 PB - Wiley CY - Oxford AN - OPUS4-52491 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahmadi, Samim A1 - Lecompagnon, Julien A1 - Hirsch, Philipp Daniel A1 - Burgholzer, P. A1 - Jung, P. A1 - Caire, G. A1 - Ziegler, Mathias T1 - Laser excited super resolution thermal imaging for nondestructive inspection of internal defects N2 - A photothermal super resolution technique is proposed for an improved inspection of internal defects. To evaluate the potential of the laser-based thermographic technique, an additively manufactured stainless steel specimen with closely spaced internal cavities is used. Four different experimental configurations in transmission, reflection, stepwise and continuous scanning are investigated. The applied image post-processing method is based on compressed sensing and makes use of the block sparsity from multiple measurement events. This concerted approach of experimental measurement strategy and numerical optimization enables the resolution of internal defects and outperforms conventional thermographic inspection techniques. KW - Super Resolution KW - Laser Thermography KW - Non Destructive Testing KW - Comressed Sensing KW - Inverse Problem KW - Thermography PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519016 DO - https://doi.org/10.1038/s41598-020-77979-y VL - 10 IS - 1 SP - 22357 PB - Springer Nature AN - OPUS4-51901 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Unnikrishnakurup, Sreedhar A1 - Myrach, Philipp A1 - Polomski, Benjamin A1 - Le Claire, Elisabeth A1 - Vengara, N. A1 - Balasubramaniam, Krishnan A1 - Ziegler, Mathias T1 - Thermographic crack detection in hot steel surfaces N2 - The detection and characterization of surface cracks in steel specimens prior to damage is a technologically and economically highly significant task and is of utmost importance when it comes to safety-relevant structures. In steel production where steel billets at high temperatures have to be inspected while moving a number of well-established NDT methods cannot be applied. Laser thermography however is a promising candidate to serve as a fast, non-contact and remote tool in this case. We present a study that shows that the crack detection capabilities of laser thermography can be extended also to specimens at high temperature. A combination of inductive and laser heating allows to systematically study the contrast formation as well as the optimization of the important measurement parameters. The experiments are accompanied by FEM simulations that provide a better insight of the physical correlations and support the experimental developments. The aim of these studies is to develop a system with high inspection speed and detection performance to be in-line operated under the hostile environment of steel production lines. T2 - 19th World Conference on Non-Destructive Testing (WCNDT 2016) CY - Munich, Germany DA - 13.06.2016 KW - In-line Monitoring KW - Laser Infrared thermography KW - Cracks KW - Induction heating KW - Steel billets KW - FEM simulation PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-389161 UR - http://ndt.net/?id=19573 SN - 1435-4934 VL - 21 IS - 7 SP - 1 EP - 8 PB - NDT.net CY - Kirchwald AN - OPUS4-38916 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - You, Zengchao A1 - Winckelmann, Alexander A1 - Vogl, Jochen A1 - Recknagel, Sebastian A1 - Abad Andrade, Carlos Enrique T1 - Determination of calcium, iron, and selenium in human serum by isotope dilution analysis using nitrogen microwave inductively coupled atmospheric pressure plasma mass spectrometry (MICAP-MS) N2 - In this study, we demonstrate the applicability of nitrogen microwave inductively coupled atmospheric pressure mass spectrometry (MICAP-MS) for Ca, Fe, and Se quantification in human serum using isotope dilution (ID) analysis. The matrix tolerance of MICAP-MS in Na matrix was investigated, uncovering that high Na levels can suppress the signal intensity. This suppression is likely due to the plasma loading and the space charge effect. Moreover, 40Ca and 44Ca isotopic fractionation was noted at elevated Na concentration. Nine certified serum samples were analyzed using both external calibration and ID analysis. Overestimation of Cr, Zn, As, and Se was found in the results of external calibration, which might be resulted from C-induced polyatomic interference and signal enhancement, respectively. Further investigations performed with methanol showed a similar enhancement effect for Zn, As, and Se, potentially supporting this assumption. The mass concentrations determined with ID analysis show metrological compatibility with the reference values, indicating that MICAP-MS combined with ID analysis can be a promising method for precise Ca, Fe, and Se determination. Moreover, this combination reduces the influences of matrix effects, broadening the applicability of MICAP-MS for samples with complex matrix. KW - Selenium KW - Nitrogen microwave inductively coupled atmospheric pressure mass spectrometry KW - Isotope dilution KW - Human serum KW - Calcium KW - Iron PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-598664 DO - https://doi.org/10.1007/s00216-024-05274-0 SN - 1618-2642 SP - 3117 EP - 3125 PB - Springer CY - Berlin AN - OPUS4-59866 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krankenhagen, Rainer A1 - Ziegler, Mathias A1 - Maierhofer, Christiane ED - Maldague, X. T1 - Systematic errors in the evaluation of uncorrected data from thermographic lock-in measurements N2 - Lock-in thermography (LT) is based on the correct evaluation of phase differences between the temperature oscillations at different surface regions of the object under test during periodic heating. Since the usual heating procedures contain a DC component, the actual heating pattern achieved is not harmonic. This causes systematic deviations when phase differences are determined by means of harmonic analysis, e.g. with FFT analysis. The resulting errors depend clearly on the ratio between DC and AC amplitude, which is demonstrated at simulated and experimentally recorded temperature transients. Further experimental LT data obtained by different oscillating energy inputs showed a variety of possible shapes of transients with different DC components. T2 - 14th QIRT Conference CY - Berlin, Germany DA - 26.06.2018 KW - NDT KW - Lock-in Thermography KW - FFT PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-453768 SP - 539 EP - 547 PB - QIRT Council AN - OPUS4-45376 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -