Teruo Negishi

Simultaneous measurement of electrical and magnetic properties of a spherical sample

A method using a solenoid coil for simultaneously estimating the electric and magnetic properties of a spherical conductor was studied. These properties are estimated by finding the difference in the complex impedance of the coil with and without a sample to find out the measuring value that best coincides with the theoretical value. A new formula applicable to a nonmagnetic, a magnetic or a superconductive spherical sample was derived. The conductivities a and permeabilities /spl mu/ measured by this method and by the conventional methods were compared using various samples. The deviations were no larger than 3% for a nonmagnetic samples, and 1.5% for /spl mu/ of magnetic samples.

Simultaneous measurement of size and electromagnetic property of multilayered spherical sample

Basic theoretical analyses to detect undesirable foreign metal pieces in the meat being processed have already been carried out. In this study, taking the low conductivity of meat into account, a double-layered spherical sample structure which enables easy analyses was selected. In order to detect these conductive materials, analyses of the difference in the impedance of a circular coil with, and another one without, a double-layered spherical conductor were made. In this way, a new formula for obtaining the electromagnetic properties of a double-layered spherical sample was derived. The process of deriving the new formula is explained. The calculated value was compared with the experimental value. Their values had a close correlation.

Fabrication of 10,000A/cm2 Class Bi-2223 Sintered Bulk

Many kinds of preparation processes of calcined powder have been proposed for producing sintered bulk Bi-2223. We adopted a coprecipitatcd method that is able to form homogeneous and fine powders that lead to facilitating synthesis in the calcination and sintering reaction. However, calcination condition of coprccipitated powder for obtaining high Jc sintered bulk is delicate. Oxide superconducting calcined powder adsorbs firstly atmospheric moisture, then reacts with carbon dioxide, which aim deteriorate the superconducting properties of the oxide superconductor. Carbon that is included in the calcined powder segregates in crystal grain boundaries during sintering process. This segregation decreases Jc, by cause in weak links, preventing superconducting current from flowing across grain boundaries. We reconsidered the calcined powder preparation process. By improving a solvent removal method after a wet pulverizing method where moisture is easily adsorbed, it was possible to reduce the carbon content to under 0.03wt%. The calcined powder was pressed into 20 mm diameter pellets and then sintered at 850 °C for 50hr in air with an intermediate pressing by the CIP (cold isostatic press) method. The Jc of the sintered bulk was increased to be 10,000A/cm2, reproducibly.

A double coil method for simultaneous measurement of electrical and magnetic properties of spherical sample

We have been studying a method for simultaneously measuring the electrical and magnetic properties of spherical sample (SRPM method). In the SRPM method, the differences in the impedance of a circular coil with a sample and an identical one without a sample are vectorially measured, and the values are compared with the one calculated by the formulae including the sample parameters. Then the properties are simultaneously estimated by finding their agreements. As the sample is inserted into the coil and pulled out of the coil alternately, the properties obtained by this method often contain the large error caused by the deviation from ideal condition of the position the sample and the coil. For the improvement of such situation, a method using double coils is proposed. The spherical sample is coaxially placed on the center of both coils, and the connections of the two coils can be switched to pass the current through the coils in the same direction or in opposite directions. A new formulae for obtaining the difference in the impedance of the coil is derived to apply to such conditions. In order to confirm the validity of these formulae, the conductivity estimated by the SRPM method and the DC four-probe method were compared. They are within 1.8%.

Simultaneous measurement of the size and the electromagnetic property of a double-layered spherical sample

Basic theoretical analyses to detect undesirable foreign metal pieces in the meat being processed have already been carried out. In this study, taking the low conductivity of meat into account, a double-layered spherical sample structure which enables easy analyses was selected. In order to detect these conductive materials, analyses of the difference in the impedance of a circular coil with, and another one without a double-layered spherical conductor were made. In this way, a new formula for obtaining the electromagnetic properties of a double-layered spherical sample was derived. The process of deriving the new formula is explained. The calculated value was compared with the experimental value. Their values had a close correlation.

A method to evaluate cracks in a superconductive cylinder used to shield weak magnetic fields

To survey the local superconductivity and cracks in a large superconductor, a method for estimating the property from the difference in the real component /spl Delta/R and imaginary component /spl Delta/X of the complex impedance of a coil with a sample and another without one is proposed. This method was applied to two samples one which was superconductive and one not superconductive at 77.3 K. It is understood that samples become superconductive when /spl Delta/R is sufficiently near 0 and /spl Delta/X is negative. The relation between two superconductors, one without and the other with artificially induced cracks was experimentally investigated. It was confirmed that the property of the sample with cracks deviated from superconductivity. As for a superconductive cylinder of 0.5 m in diameter and 1 m in length open at one end, /spl Delta/R and /spl Delta/X at various points on the wall and at the closed end were measured at 77.3 K and the values of /spl Delta/R were sufficiently near 0. All values of /spl Delta/X were negative. The magnetic shielding effect was confirmed to be 1/20000.