Mineo Itoh

The improvement in magnetic shielding by use of a double-cylinder configuration of high-Tc oxide superconductors

The critical current density (Jc) of high critical temperature (Tc) copper-oxide superconductors is an important parameter in magnetic shielding. However, it was determined that the value of Jc was not closely related to the degree of magnetic shielding. The degree of shielding can be improved by the use of a configuration of superimposed double cylinders constructed of a copper-oxide superconductor. Experimental results indicate that the characteristics of the double-cylinder system (such as the effect of the excitation magnetic field on the magnetic field within the cylinders, and the distribution of the magnetically shielded field along the axial direction of the cylinders) are improved over those of single superconducting cylinders.

Superconducting transition temperature versus thickness of Nb film on various substrates

Dependence of superconducting transition temperature on the thickness of Nb films deposited upon several kinds of substrates by means of rf sputtering was studied in search of rudimental data necessary in fabricating variable thickness microbridge type Josephson junctions. The transition temperature was found to lower with the decrease of Nb film thickness. The lowering characteristics of the transition temperature were found to vary in accordance with whether the substrate surface was amorphous or crystalline. The cause of the variance was studied on thin films with the aid of x‐ray diffraction pattern analysis and measurement of film resistance.

Preparation of Superconducting Y-Ba-Cu-O Thick Film

During sintering, superconducting copper-oxide films commonly have a high chemical activity with substrate materials, which results in poor superconductivity. In this research, the substrate is prepared by coating multiple non-superconducting Y-Ba-Cu-O films on alumina. The superconducting Y-Ba-Cu-O thick films were prepared by mixing powders Y2O3, BaCO3 and CuO, making a paste by mixing this noncalcined mixture with solvent, coating it on to a film-coated substrate using a painting or printing method, and then sintering the specimen. The thick films have positive superconductive characteristics at high temperatures.

Influence of silver on critical current of the Y–Ba–Cu–O superconductor

Electrical properties of Y--Ba--Cu--O superconductors, such as the critical current density and the zero-resistance temperature, are systematically improved by changing the compression pressure during the formation process of the specimens. Also, by changing the silver powder content of the superconducting Y--Ba--Cu--O powder, the critical current density and the zero-resistance temperature are remarkably improved. The resistance-drop temperature is insensitive to changes in the compression pressure, silver content, and magnetic field, whether the field is applied perpendicular to the specimens. The critical current density of the specimens with and without silver decreases exponentially with the perpendicular magnetic field. The critical current densities of specimens without silver showed much lower sensitivity to perpendicularly applied magnetic fields than those of the specimens having a silver content. Along with the above improvements, the present paper also examines several factors that affect the superconducting characteristics. These factors include impurities in the air and strong magnetic fields.

Improvement in magnetic shielding by the superposition of a magnetic cylinder over a copper-oxide superconducting cylinder

Magnetic shielding was shown to be improved by superimposing a magnet cylinder over a superconducting cylinder. Examples of such configurations are soft iron and electromagnetic steel cylinders over a copper-oxide superconducting cylinder. The value of the magnetic shielded field for the superimposed cylinder was found to be several times more than that of single superconducting cylinders such as YBCO or a BPSCCO cylinder. Experimental results reveal good characteristics which include the effects of the excitation magnetic field on the inner magnetic field within both the single superconducting and superimposed cylinders, the temporal change of the trapped magnetic field within the superconducting cylinder, the distribution of the magnetic shielded field along the axial direction of the superimposed cylinders, and the relationship between the length of the magnetic cylinder and the shielding effect.<<ETX>>

Influence of wall thickness on magnetic shielding effects of BPSCCO cylinders

The critical current density (J c ) of high critical temperature (T c ) superconductor is an important parameter in magnetic shielding. However, it is difficult to fabricate very high-J c material. The present research group has been improving magnetic shielding effects for high-T c , superconducting cylinders by using special techniques. As one of the basic research areas for the improvement of magnetic shielding effects and the fabrication of large sized cylinders, the present paper analyzes the relationship between the wall thickness (w) of the cylinder and the maximum magnetic shielded field (B s ) by use of critical state models. The values of B s are systematically measured by changing the w values of BPSCCO cylinders at a temperature of 77.4 K. It is found that the values of B s do not change linearly with the values of w, and the theoretical values of B s agree well with the experimental values. The temporal change of the maximum magnetic trapped field (B t ) is also analyzed by Anderson-Kim flux-creep theory, with the experimental results of the temporal change of B t agreeing well the theoretical results. It is observed the periodic dependence of DC-SQUID voltage on the applied magnetic field in the center of the superconducting cylinder.

Influence of Carbon on Critical Temperatures of Superconducting Y-Ba-Cu-O

High Tc copper oxide superconductors, such as Y-Ba-Cu-O, commonly have a high chemical activity during sintering. Y-Ba-Cu-O superconductors are influenced by impurities in air, which cause degradation of the superconducting properties, critical current density (Jc) and temperature of zero resistance (Tczero). XPS analysis of low Jc and Tczero materials shows a presence of carbon in a higher amount compared to high Jc and Tczero materials. This paper shows that Jc and Tczero are very susceptible to impure gases in air.

Highly sensitive magnetic sensor made with a superconducting Y-Ba-Cu-O thick film

In the research, Y-Ba-Cu-O (YBCO) thick film was fabricated to form a highly sensitive magnetic sensor, constructed to maintain the superconducting state at the boiling point of liquid nitrogen (77.4 K). Superconducting film will, in general, break the superconducting state of the flow of current at the value of current density J greater than that of the critical current density J/sub c/, when the resistance R/sub sen/ to the flow of current occurs. The magnetic sensitivity increases as the value of the resistivity /spl rho//sub seu/ of R/sub sen/ decreases. The value of /spl rho//sub sen/ can be readily controlled by the value of J. The average sensitivity S of this magnetic sensor was determined as about 154%/gauss, over the magnetic range of 0 gauss to /spl plusmn/40 gauss. In addition,the sensitivity is about 154 times that of a giant magneto-resistance sensor. The paper examines the fabrication process and conditions, the characteristics of S as related to /spl rho//sub sen/, and the magnetic response of the highly sensitive magnetic sensor.

RF Magnetic Shielding Effects of a Compound Plate Constructed From Bincho-Charcoal and Ferrite Plates

With rapid development in the field of information technology, there has been increased interest for electromagnetic shielding in the radio frequency (RF) region. An excellent RF magnetic shielding material can be realized by the use of bincho-charcoal, a high quality charcoal found in Japan, due to its very large value of relative permittivity in the RF region. The present paper has improved the RF magnetic shielding characteristics of a bincho-charcoal plate to realize a broadband frequency by the superposition of a ferrite plate over the bincho-charcoal plate. This configuration is termed the compound plate. The RF magnetic shielding effects of the compound plate have been examined, including the characteristics of the RF magnetic effect against both the frequency and the RF magnetic power. In addition, RF electric shielding effects have been examined as functions of the frequency and the RF electric power

Highly accurate measurement of sheet thickness: the planar error correction

In the present study, the authors describe a system using optical and magnetic sensors to measure the thickness of polymer sheets accurately. A newly developed planar error correction method used in the manufacturing process of the sheet is also presented. The system was drastically improved for the precision of measurement of the polymer sheet, resulting in a precision of /spl plusmn/1% or less. As a result, we have succeeded to produce sheets with thickness of 300 /spl mu/m at a manufacturing process speed of approximately 30 m/min.