TY - JOUR A1 - Krause, Gregor A1 - Meurer, D. A1 - Klee, D. T1 - Space Charge Formation Related to the Morphology of Polymers JF - ISE 6 : 6th International symposium on electrets : Papers Y1 - 1988 N1 - International Symposium on Electrets <6, 1988, Oxford> PB - IEEE CY - Piscataway, NY ER - TY - JOUR A1 - Krause, Gregor A1 - Meurer, D. A1 - Klee, D. T1 - Space charge formation related to the morphology of polymers JF - IEEE Transaction on Electrical Insulation. Vol. 24 (1989), H. No. 3 Y1 - 1989 N1 - Digital Object Identifier 10.1109/14.30883 SP - 215 EP - 222 ER - TY - JOUR A1 - Krause, Gregor A1 - Göttlich, S. A1 - Möller, K. A1 - Meurer, D. T1 - Space Charge Phenomena in Partially Crystalline Polymers: On-Line Measurement of Charge Carrier Motion under High AC-Field Strength / G. Krause, S. Göttlich, K. Möller, D. Meurer JF - Proceedings of the 3rd International Conference on Conduction and Breakdown in Solid Dielectrics : Trondheim, Norway ... 1989 Y1 - 1989 N1 - International Conference on Conduction and Breakdown in Solid Dielectrics <3, 1989, Trondheim> PB - IEEE CY - Piscataway, N.J. ER - TY - JOUR A1 - Krause, Gregor A1 - Fruth, Bernhard T1 - Dielectric Properties of Polyolefins Stressed by High Electrical Fields. Fruth, B. ; Krause, G. Y1 - 1987 N1 - Fifth International Symposium on High Voltage Engineering : Proceedings; Braunschweig, Stadthalle, August, 24-28, 1987 / International Symposium on High Voltage Engineering <5, 1987, Braunschweig> ER - TY - JOUR A1 - Krause, Gregor A1 - Fruth, B. T1 - Dielectric Properties of Polyolefins Stressed by High Electrical Fields / Fruth, B. ; Krause, G. JF - Plenary lectures and contributions presented at the International Symposium on Polymer Materials : held in San Sebastian (Donostia), Spain, 31 August - 4 September, 1987 / symposium ed. G. M. Guzmán ; A. Santamaria Y1 - 1988 SN - 3-85739-220-7 N1 - International Symposium on Polymer Materials <1987, San Sebastián, Golfo de Vizcaya> PB - Huethig & Wepf CY - Basel ER - TY - JOUR A1 - Krause, Gregor T1 - High Field Phenomena of Polymeric Insulation Investigated at PE Needle-Plane Specimen JF - Seventh International Symposium on High Voltage Engineering : Dresden, August 26 - 30, 1991 / Technische Universität Dresden Y1 - 1991 N1 - International Symposium on High Voltage Engineering ; (7, 1991, Dresden); International Symposium on High Voltage Engineering (ISH) ; (7 : ; 1991.08.26-30 : ; Dresden) PB - TU Dresden CY - Dresden ER - TY - JOUR A1 - Kraff, Oliver A1 - Wrede, Karsten H. A1 - Schoemberg, Tobias A1 - Dammann, Philipp A1 - Noureddine, Yacine A1 - Orzada, Stephan A1 - Ladd, Mark E. A1 - Bitz, Andreas T1 - MR safety assessment of potential RF heating from cranial fixation plates at 7 T JF - Medical Physics Y1 - 2013 U6 - http://dx.doi.org/10.1118/1.4795347 SN - 2473-4209 VL - 40 IS - 4 SP - 042302-1 EP - 042302-10 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Kruszona, Stefan A1 - Orzada, Stephan A1 - Schaefer, Lena C. A1 - Theysohn, Jens M. A1 - Maderwald, Stefan A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - An eight-channel phased array RF coil for spine MR imaging at 7 T JF - Investigative Radiology Y1 - 2009 U6 - http://dx.doi.org/10.1097/RLI.0b013e3181b24ab7 SN - 1536-0210 VL - 44 IS - 11 SP - 734 EP - 740 PB - Lippincott Williams & Wilkins ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Dammann, Philipp A1 - Ladd, Susanne C. A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - An eight-channel transmit/receive multipurpose coil for musculoskeletal MR imaging at 7 T JF - Medical Physics N2 - Purpose: MRI plays a leading diagnostic role in assessing the musculoskeletal (MSK) system and is well established for most questions at clinically used field strengths (up to 3 T). However, there are still limitations in imaging early stages of cartilage degeneration, very fine tendons and ligaments, or in locating nerve lesions, for example. 7 T MRI of the knee has already received increasing attention in the current published literature, but there is a strong need to develop new radiofrequency (RF) coils to assess more regions of the MSK system. In this work, an eight-channel transmit/receive RF array was built as a multipurpose coil for imaging some of the thus far neglected regions. An extensive coil characterization protocol and first in vivo results of the human wrist, shoulder, elbow, knee, and ankle imaged at 7 T will be presented. Methods: Eight surface loop coils with a dimension ofurn:x-wiley:00942405:media:mp7176:mp7176-math-0001 were machined from FR4 circuit board material. To facilitate easy positioning, two coil clusters, each with four loop elements, were combined to one RF transmit/receive array. An overlapped and shifted arrangement of the coil elements was chosen to reduce the mutual inductance between neighboring coils. A phantom made of body-simulating liquid was used for tuning and matching on the bench. Afterward, the S-parameters were verified on a human wrist, elbow, and shoulder. For safety validation, a detailed compliance test was performed including full wave simulations of the RF field distribution and the corresponding specific absorption rate (SAR) for all joints. In vivo images of four volunteers were assessed with gradient echo and spin echo sequences modified to obtain optimal image contrast, full anatomic coverage, and the highest spatial resolution within a reasonable acquisition time. The performance of the RF coil was additionally evaluated by in vivo B1 mapping. Results: A comparison of B1 per unit power, flip angle distribution, and anatomic images showed a fairly homogeneous excitation for the smaller joints (elbow, wrist, and ankle), while for the larger joints, the shoulder and especially the knee, B1 inhomogeneities and limited penetration depth were more pronounced. However, the greater part of the shoulder joint could be imaged.In vivo images rendered very fine anatomic details such as fascicles of the median nerve and the branching of the nerve bundles. High-resolution images of cartilage, labrum, and tendons could be acquired. Additionally, turbo spin echo (TSE) and inversion recovery sequences performed very well. Conclusions: This study demonstrates that the concept of two four-channel transmit/receive RF arrays can be used as a multipurpose coil for high-resolutionin vivo MR imaging of the musculoskeletal system at 7 T. Not only gradient echo but also typical clinical and SAR-intensive sequences such as STIR and TSE performed well. Imaging of small structures and peripheral nerves could in particular benefit from this technique. Y1 - 2010 U6 - http://dx.doi.org/10.1118/1.3517176 SN - 2473-4209 VL - 37 IS - 12 SP - 6368 EP - 6376 PB - Wiley CY - Hoboken, NJ ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Breyer, Tobias A1 - Kruszona, Stefan A1 - Maderwald, Stefan A1 - Brote, Irina A1 - Gizewski, Elke R. A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - A transmit/receive radiofrequency array for imaging the carotid arteries at 7 Tesla: coil design and first in vivo results JF - Investigative Radiology N2 - Objective: To develop a transmit/receive radiofrequency (RF) array for magnetic resonance imaging (MRI) of the carotid arteries at 7 T. The prototype is characterized in numerical simulations and bench measurements, and the feasibility of plaque imaging at 7 T is demonstrated in first in vivo images. Materials and Methods: The RF phased array coil consists of 8 surface loop coils. To allow imaging of both sides of the neck, the RF array is divided into 2 coil clusters, each with 4 overlapping loop elements. For safety validation, numerical computations of the RF field distribution and the corresponding specific absorption rate were performed on the basis of a heterogeneous human body model. To validate the coil model, maps of the transmit B1+ field were compared between simulation and measurement. In vivo images of a healthy volunteer and a patient (ulcerating plaque and a 50% stenosis of the right internal carotid artery) were acquired using a 3-dimensional FLASH sequence with a high isotropic spatial resolution of 0.54 mm as well as using pulse-triggered proton density (PD)/T2-weighted turbo spin echo sequences. Results: Measurements of the S-parameters yielded a reflection and isolation of the coil elements of better than −18 and −13 dB, respectively. Measurements of the g-factor indicated good image quality for parallel imaging acceleration factors up to 2.4. A similar distribution and a very good match of the absolute values were found between the measured and simulated B1+ transmit RF field for the validation of the coil model. In vivo images revealed good signal excitation of both sides of the neck and a high vessel-to-background image contrast for the noncontrast-enhanced 3-dimensional FLASH sequence. Imaging at 7 T could depict the extent of stenosis, and revealed the disruption and ulcer of the plaque. Conclusions: This study demonstrates that 2 four-channel transmit/receive RF arrays for each side of the neck is a suitable concept for in vivo MRI of the carotid arteries at 7 Tesla. Further studies are needed to explore and exploit the full potential of 7 T high-field MRI for carotid atherosclerotic plaque imaging. Y1 - 2011 U6 - http://dx.doi.org/10.1097/RLI.0b013e318206cee4 SN - 1536-0210 VL - 46 IS - 4 SP - 246 EP - 254 PB - Wolters Kluwer CY - Köln ER - TY - JOUR A1 - Kowalewski, Paul A1 - Bragard, Michael A1 - Hüning, Felix A1 - De Doncker, Rik W. T1 - An inexpensive Wiegand-sensor-based rotary encoder without rotating magnets for use in electrical drives JF - IEEE Transactions on Instrumentation and Measurement N2 - This paper introduces an inexpensive Wiegand-sensor-based rotary encoder that avoids rotating magnets and is suitable for electrical-drive applications. So far, Wiegand-sensor-based encoders usually include a magnetic pole wheel with rotating permanent magnets. These encoders combine the disadvantages of an increased magnet demand and a limited maximal speed due to the centripetal force acting on the rotating magnets. The proposed approach reduces the total demand of permanent magnets drastically. Moreover, the rotating part is manufacturable from a single piece of steel, which makes it very robust and cheap. This work presents the theoretical operating principle of the proposed approach and validates its benefits on a hardware prototype. The presented proof-of-concept prototype achieves a mechanical resolution of 4.5 ° by using only 4 permanent magnets, 2Wiegand sensors and a rotating steel gear wheel with 20 teeth. KW - Rotary encoder KW - Wiegand sensor Y1 - 2023 U6 - http://dx.doi.org/10.1109/TIM.2023.3326166 SN - 0018-9456 (Print) SN - 1557-9662 (Online) N1 - Early Access SP - 10 Seiten PB - IEEE ER - TY - JOUR A1 - Kobus, Thiele A1 - Bitz, Andreas A1 - Uden, Mark J. van A1 - Lagemaat, Miram W. A1 - Rothgang, Eva A1 - Orzada, Stephan A1 - Heerschap, Arend A1 - Scheenen, Tom W. J. T1 - In vivo 31P MR spectroscopic imaging of the human prostate at 7 T: safety and feasibility JF - Magnetic Resonance in Medicine N2 - 31P MR spectroscopic imaging of the human prostate provides information about phosphorylated metabolites that could be used for prostate cancer characterization. The sensitivity of a magnetic field strength of 7 T might enable 3D 31P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a 31P endorectal coil was developed and combined with an eight-channel 1H body-array coil to relate metabolic information to anatomical location. An extensive safety validation was performed to evaluate the specific absorption rate, the radiofrequency field distribution, and the temperature distribution of both coils. This validation consisted of detailed Finite Integration Technique simulations, confirmed by MR thermometry and Burn:x-wiley:07403194:media:MRM24175:tex2gif-stack-1 measurements in a phantom and in vivo temperature measurements. The safety studies demonstrated that the presence of the 31P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight-channel 1H array coil. To stay within a 10 g averaged local specific absorption rate of 10 W/kg, a maximum time-averaged input power of 33 W for the 1H array coil was allowed. For transmitting with the 31P endorectal coil, our safety limit of less than 1°C temperature increase in vivo during a 15-min MR spectroscopic imaging experiment was reached at a time-averaged input power of 1.9 W. With this power setting, a second in vivo measurement was performed on a healthy volunteer. Using adiabatic excitation, 3D 31P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm3. The spectral resolution enabled the separate detection of phosphocholine, phosphoethanolamine, inorganic phosphate, and other metabolites that could play an important role in the characterization of prostate cancer. Y1 - 2012 U6 - http://dx.doi.org/10.1002/mrm.24175 SN - 1522-2594 VL - 68 IS - 6 SP - 1683 EP - 1695 PB - Wiley-Liss CY - New York ER - TY - JOUR A1 - Klomp, D. W. J. A1 - Bitz, Andreas A1 - Heerschap, A. A1 - Scheenen, T. W. J. T1 - Proton spectroscopic imaging of the human prostate at 7 T JF - NMR in Biomedicine Y1 - 2009 U6 - http://dx.doi.org/10.1002/nbm.1360 SN - 1099-1492 VL - 22 IS - 5 SP - 495 EP - 501 ER - TY - JOUR A1 - Klinge, Uwe A1 - Otto, Jens A1 - Mühl, Thomas T1 - High Structural Stability of Textile Implants Prevents Pore Collapse and Preserves Effective Porosity at Strain JF - BioMed Research International Y1 - 2015 U6 - http://dx.doi.org/10.1155/2015/953209 SN - 2314-6133 (Print) SN - 2314-6141 (Online) N1 - Article ID: 953209 VL - 2015 ER - TY - JOUR A1 - Jens, Otto A1 - Kaldenhoff, E. A1 - Kirschner-Hermanns, R. A1 - Mühl, Thomas A1 - Klinge, Uwe T1 - Elongation of textile pelvic floor implants under load is related to complete loss of effective porosity, thereby favoring incorporation in scar plates JF - Journal of biomedical materials research. Part A N2 - Use of textile structures for reinforcement of pelvic floor structures has to consider mechanical forces to the implant, which are quite different to the tension free conditions of the abdominal wall. Thus, biomechanical analysis of textile devices has to include the impact of strain on stretchability and effective porosity. Prolift® and Prolift + M®, developed for tension free conditions, were tested by measuring stretchability and effective porosity applying mechanical strain. For comparison, we used Dynamesh-PR4®, which was designed for pelvic floor repair to withstand mechanical strain. Prolift® at rest showed moderate porosity with little stretchability but complete loss of effective porosity at strain of 4.9 N/cm. Prolift + M® revealed an increased porosity at rest, but at strain showed high stretchability, with subsequent loss of effective porosity at strain of 2.5 N/cm. Dynamesh PR4® preserved its high porosity even under strain, but as consequence of limited stretchability. Though in tension free conditions Prolift® and Prolift + M® can be considered as large pore class I meshes, application of mechanical strain rapidly lead to collapse of pores. The loss of porosity at mechanical stress can be prevented by constructions with high structural stability. Assessment of porosity under strain was found helpful to define requirements for pelvic floor devices. Clinical studies have to prove whether devices with high porosity as well as high structural stability can improve the patients' outcome. Y1 - 2014 U6 - http://dx.doi.org/10.1002/jbm.a.34767 SN - 1552-4965 VL - 102 IS - 4 SP - 1079 EP - 1084 PB - Wiley CY - New York ER - TY - JOUR A1 - Hüning, Felix A1 - Wilke, I. A1 - Nakielski, G. A1 - Kotzler, J. T1 - Dynamic conductivity of YBCO thin films from low to very high frequencies / Wilke, I. ; Nakielski, G. ; Kotzler, J. ; Subke, K. O. ; Jaekel, C. ; Hüning, F. ; Roskos, H. G. ; Kurz, Heinrich JF - Applied superconductivity 1997 : proceedings of EUCAS 1997, the Third European Conference on Applied Superconductivity, held in the Netherlands, 30 June - 3 July 1997 / ed. by H. Rogalla Y1 - 1997 SN - 0-7503-0487-1 N1 - Institute of Physics conference series 158 SP - 121 EP - 124 PB - IOP CY - Bristol ER - TY - JOUR A1 - Hüning, Felix A1 - Sparta, K. A1 - Redhammer, G. J. A1 - Roussel, P. T1 - Structural Phase Transition in the 2D Spin Dimer Compound SrCu2(BO3)2 / Sparta, K. ; Redhammer, G. J. ; Roussel, P. ; Heger, G. ; Roth, G. ; Ionescu, A. Lemmens, P. ; Grove, M. ; Güntherrodt, G. ; Hüning, F. ; Lueken, H. ; Kageyama, H. ; Onizuka, K ; Ueda JF - The European Physical Journal B - Condensed Matter and Complex Systems. 19 (2001), H. 4 Y1 - 2001 SN - 1434-6036 SP - 507 EP - 516 PB - - ER - TY - JOUR A1 - Hüning, Felix A1 - Luken, Heiko A1 - Schilder, Herbert A1 - Eifert, Thomas T1 - Magnetochemistry: Compounds and Concepts / Lueken, Heiko ; Schilder, Herbert ; Eifert, Thomas ; Handrick, Klaus ; Hüning, Felix JF - Advances in Solid State Physics. 201 (2001) Y1 - 2001 SP - 515 EP - 532 PB - - ER - TY - JOUR A1 - Hüning, Felix A1 - Leineweber, A. A1 - Jacobs, H. A1 - Lueken, H. T1 - ε-Fe3N: magnetic structure, magnetization and temperature dependent disorder of nitrogen / Leineweber, A. ; Jacobs, H. ; Hüning, F. ; Lueken, H. ; Schilder, H. ; Kockelmann, W. JF - Journal of Alloys and Compounds. 288 (1999), H. 1-2 N2 - ε-Fe3N has been investigated by time-of-flight neutron diffraction (temperature range 4.2–618 K) and SQUID magnetometry (2–700 K, B≤5 T). A ferromagnetic spin structure is observed with magnetic moments oriented perpendicular to the c-axis of the hexagonal nuclear structure. The magnetic saturation moment of iron is 2.2 μB at 4.2 K from neutron diffraction and 2.0 μB from magnetic measurements and decreases in a Brillouin-like manner on heating to TC=575 K. Above 450 K an increasing but reversible disorder of the nitrogen partial structure is observed. Y1 - 1999 SN - 1873-4669 VL - 288 IS - 1-2 SP - 79 EP - 87 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hüning, Felix A1 - Leineweber, A. A1 - Jacobs, H. A1 - Lueken, H. T1 - Nitrogen Ordering and ferromagnetic properties of -Fe3N1+x (0.10  x  0.39) and -Fe3(N0.80C0.20)1.38 / Leineweber, A. ; Jacobs, H. ; Hüning, F. ; Lueken, H. ; Kockelmann, W. JF - Journal of Alloys and Compounds. 316 (2001), H. 1-2 Y1 - 2001 SN - 1873-4669 SP - 21 EP - 38 PB - - ER -