Use of high-temperature superconducting films in superconducting bearings.

We have investigated the effect of high-temperature superconductor (HTS) films deposited on substrates that are placed above bulk HTSs in an attempt to reduce rotational drag in superconducting bearings composed of a permanent magnet levitated above the film/bulk HTS combination. According to the critical state model, hysteresis energy loss is inversely proportional to critical current density, J{sub c}, and because HTS films typically have much higher J{sub c} than that of bulk HTS, the film/bulk combination was expected to reduce rotational losses by at least one order of magnitude in the coefficient of fiction, which in turn is a measure of the hysteresis losses. We measured rotational losses of a superconducting bearing in a vacuum chamber and compared the losses with and without a film present. The experimental results showed that contrary to expectation, the rotational losses are increased by the film. These results are discussed in terms of flux drag through the film, as well as of the critical state model

S-UTD-CH model in multiple diffraction geometry [Dişbükey zarf tekni?ine dayali e?im kirinimi modelinin çoklu kirinim geometrisinde kullanilmasi]

2010 7th National Conference on Electrical, Electronics and Computer Engineering, ELECO 2010Calculation of relative path loss of electromagnetic wave in multiple diffraction geometries is important. In this respect, many diffraction models have been introduced. There is a trade-off between computation time and accuracy of estimated field strength. Some models have higher computation time with lower accuracy, or vice versa. In this study, Slope UTD with Convex Hull (S-UTD-CH), optimum model for accuracy and computation time, is introduced briefly, and simulation results are given. S-UTD-CH model is based on slope diffraction (S-UTD) including slope terms of UTD, and convex hull (CH) method. It is observed in simulation how polarization types, interior wedge angle, conductivity and relative permittivity of wedge affects the relative path loss. Moreover, comparative results of different models with respect to accuracy and computational time for a given profile are presented in this study

Application of S-UTD-CH model into multiple diffraction scenarios

Propagation prediction models based on ray tracing in coverage estimation for digital broadcasting systems are compared. Geometrical Theory of Diffraction (GTD), Slope Uniform Theory of Diffraction (S-UTD), and Slope UTD with Convex Hull (S-UTD-CH) models are compared for computation time and propagation path loss. S-UTD-CH model is optimum model with respect to computation time and relative path loss. © 2013 Mehmet Baris Tabakcioglu and Ahmet Cansiz

Use of thin films in high-temperature superconducting bearings.

In a PM/HTS bearing, locating a thin-film HTS above a bulk HTS was expected to maintain the large levitation force provided by the bulk with a lower rotational drag provided by the very high current density of the film. For low drag to be achieved, the thin film must shield the bulk from inhomogeneous magnetic fields. Measurement of rotational drag of a PM/HTS bearing that used a combination of bulk and film HTS showed that the thin film is not effective in reducing the rotational drag. Subsequent experiments, in which an AC coil was placed above the thin-film HTS and the magnetic field on the other side of the film was measured, showed that the thin film provides good shielding when the coil axis is perpendicular to the film surface but poor shielding when the coil axis is parallel to the surface. This is consistent with the lack of reduction in rotational drag being due to a horizontal magnetic moment of the permanent magnet. The poor shielding with the coil axis parallel to the film surface is attributed to the aspect ratio of the film and the three-dimensional nature of the current flow in the film for this coil orientation

Comparison and analyzing of propagation models with respect to material, environmental and wave properties

This paper presents a study on a class of algorithms based on Uniform Theory of Diffraction (UTD) for multiple diffractions. Within this context Slope UTD with Convex Hull (S-UTD-CH) model based on Slope UTD and Fresnel zone concept was reviewed. S-UTD-CH model can be used for fast and more accurate field prediction for multiple diffractions in transition zone. An extensive simulation results for comparison of UTD based algorithms with respect to the computation time and accuracy was provided. Furthermore, the study shows how relative permittivity constant, conductivity and inner angle of wedge and polarization type affect the relative path loss. © 2014 ACE

Determination of levitation force and pinning properties of (Sm123) 1-x(Yb211) x bulk superconductor depending on Yb211 doping ratio

The vertical force density curves of (Sm123) 1-x(Yb211)x high temperature superconductor (HTS) samples prepared by a meltpowder-melt-growth technique were measured during vertical and lateral traverses in zero field cooling (ZFC) regime for various doping levels (x). It was determined that the maximum vertical force density of the samples increases when the doping level increases and after certain level of the doping the force saturates. The pinning properties, which create attractive force, were enhanced up to a certain Yb211 doping level by introducing locally suppressed superconducting regions. These results indicate that the optimization fabrication conditions and Yb211 doping level should be further investigated for larger dimensional samples to enhance technological applicability. The frozen image model was used to predict the experimentally measured levitation force between a permanent magnet (PM) and the superconductor samples. Various configurations of the PM/HTS force interaction were tested according to the magnet and superconductor size. The doped HTS samples do not show very strong diamagnetic behavior as the frozen image model predicts. The levitation force behavior regarding the dimensions of the PM and HTS indicates an illustration how the diamagnetic behavior of the superconductor transforms into the flux pinning. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim