Shielding Behavior Research Articles

Low frequency magnetic shielding of YBa 2Cu 3O 7-δ: Ag x high temperature superconductors

Two measurement systems were used to investigate the low frequency magnetic shielding behavior of pure YBa 2Cu 3O 7−δ, silver doped YBa 2Cu 3O 7−δ, a packed powder, a laser ablated thin film and copper. It was found that factors which influence low frequency magnetic shielding include material composition, microstructure and properties, external a.c. and d.c. fields and sample dimensions. Among the experimental materials, only bulk ceramics showed good shielding factors which were constant with frequency in the range 10–3000 Hz. A macroscopic shielding current was necessary for a good shield. The thickness of the ceramic played a crucial role in shielding. Flux breakthrough occurred when the external field exceeded a certain value. The breakthrough field increased with sample thickness. The influence of d.c. fields on the shielding behaviour depended on the history and magnitudes of the fields. Magnetic shielding hysteresis was observed and its potential application is discussed.

Magnetic shielding properties of YBa2Cu3O7-x tubes

The magnetic shielding properties of polycrystalline YBa2Cu3O7-x, tubes have been investigated at 77 K in weak magnetic fields. Based on a detailed analysis of a grain-boundary weak-link picture of granular superconductors, their transport, magnetic field penetration, shielding and trapping behaviour are interpreted in terms of a critical state model. The correlation between properties and material structure is discussed.

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O7−x superconductor and their correlation with room-temperature ultrasonic measurements

The purpose of this study was to (1) examine the spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O7−x specimens over the pore fraction range 0.10–0.25 and (2) determine the viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability. Spatial variations in a.c. susceptibility were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in a.c. shielding and loss behavior. Optical quantitative image analysis on sample cross sections revealed pore fraction to be the varying microstructural feature.

Low-frequency magnetic shielding studies on high-T/sub c/ superconductor Y-Ba-Cu-O

Low frequency (10-Hz to 100-MHz) magnetic-shielding studies were performed on high-T/sub c/ superconductors Y-Ba-Cu-O to investigate the material's shielding behavior. The critical field H/sub c1/ in the superconductor was observed to be >

Electromagnetic shielding studies on plasma‐sprayed superconducting high-TCcoatings

Abstract Electromagnetic shielding behaviour of plasma-sprayed Y1Ba2Cu3O7-x coatings has been studied in the frequency range of 1 to 100 kHz. Experiments with 180 μm thick coatings on stainless-steel substrates have shown that the normal-to-superconducting phase transition introduces an additional 15 to 20 db shielding.

Fatigue crack propagation in aluminum- lithium alloy 2090: Part I. long crack behavior

A study has been made of the mechanics and mechanisms of fatigue crack propagation in a commercial plate of aluminum-lithium alloy 2090-T8E41. In Part I, the crack growth and crack shielding behavior of long (≳5 mm) through-thickness cracks is examined as a function of plate orientation and load ratio, and results compared to traditional high strength aluminum alloys. It is shown that rates of fatigue crack extension in 2090 are, in general, significantly slower (at a given stress intensity range) than in traditional alloys, although behavior is strongly anisotropic. Differences in growth rates of up to 4 orders of magnitude are observed between the L-T, T-L, and T-S orientations, which show the best crack growth resistance, and the S-L, S-T, and L + 45, which show the worst. Such behavior is attributed to the development of significant crack tip shielding (i.e., a reduction in local crack driving force), primarily resulting from the role of the crack path morphology in inducing crack deflection and crack closure from the consequent asperity wedging. Whereas crack advance perpendicular to the rolling plane (e.g., L-T,etc.) involves marked crack path deflection and branching, thereby promoting very high levels of shielding to cause the slowest growth rates, fatigue fractures parallel to the rolling plane (e.g., S-L,etc.) occur by an intergranular, delamination-type separation, with much lower shielding levels to give the fastest growth rates. The implications of such “extrinsic toughening” effects on the fracture and fatigue properties of aluminum-lithium alloys are discussed in detail.

Oxygen-ordering and ac-susceptibility in polycrystalline YBa2Cu3O7−δ (δ=0.15∼0.67)

A perfect shielding behavior has been observed by ac-susceptibility measurement in a wide oxygen-deficiency range of YBa2Cu3O7−gd (δ=0.15∼0.67) and the measurement indicated the existence of a bulk superconducting phase (ortho.II) with Tc∼60K at δ∼0.5. The ortho.II superconductivity was very sensitive to the magnetic field. A detailed ac-susceptibility measurement was conducted on the quenched polycrystalline ortho.II samples with a range of measuring magnetic field. The ac-susceptibility of the ortho.II was found to be suppressed to a constant value; about 70% of the perfect one by the magnetic field of a few oersteds. Heat-treatments at low temperatures in an encapsulated condition did not alter the essential feature. The field sensitive nature of the ortho.II susceptibility was related to the weakly coupled Josephson link through ortho.II grain boundaries.

Electromagnetic shielding behavior of wire-mesh screens

The electromagnetic shielding behavior of bounded-junction wire-mesh screens is discussed in the frequency range where the individual meshes are electrically small. The screen, whose meshes are assumed to be square, is described by a equivalent sheet impedance operator. The plane-wave shielding effectiveness of a planar-mesh screen is derived. The problem of coupling between antennas on either side of the planar mesh is addressed, and its applicability to the measurement of mesh properties is described. The low-frequency electric and magnetic shielding afforded by mesh enclosures is considered. Because of the reactive character of the mesh surface, the plane-wave shielding effectiveness decreases with increasing frequency. The enclosure's magnetic-field shielding effectiveness increases with increasing frequency, but saturates at a maximum value that depends on the geometry of the enclosure, the mesh size, and the mesh wire radius. The enclosure electrostatic-field shielding effectiveness depends only on the enclosure and mesh geometries.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The investigation of the multi-shielding system of the superconducting generator

In this paper the electromagnetic shielding behavior of the multi-shielding system in superconducting synchronous generators, the influence of one screen upon the others and the sharing of fault moment among the different screens have been investigated. Definition of magnetic penetrability has been made for describing the electromagnetic shielding behaviors of screens. The influence of operation temperature of inner screen on the system was investigated too, and a method of determining the mean temperature of inner screen was proposed.

Magnetic Shielding by Superconducting Nb-40Zr-10Ti Hollow Cylinder

Magnetic shielding characteristics were investigated at 4.2°K in transverse magnetic field up to 17.5KOe for the solution treated sample and for the samples aged at 700°C for 3, 10 and 100hr after solution treated in the hollow cylinder of Nb-40Zr-10Ti alloy. It was found that there are three regions between the two critical rates of increase of the applied field, C1 and C2 (0<C1<C2), and that the magnetic shielding behavior is different corresponding to each region. The magnetic shielding field was over 17.5KOe for the sample aged at 700°C for 100hr in this alloy. Assuming that the flux front in the Bean critical state penentrates isothermally and adiabatically from outer to inner surface of the hollow cylinder, possible models were proposed to estimate the maximum and minimum values of the magnetic shielding capacity. The calculated values based on these models agreed well with the measured values.