Akihito Yahara

Magnetic shielding properties of HTc superconductor

The shielding factor of a BSCCO 2212 phase HTc superconducting cylinder had a maximum of 10-6, even though the cylinder had a length/diameter ratio large enough to expect that the shielding factor exceeded 10-8. Two models are proposed to discuss the leakage of the magnetic field in the superconducting cylinder under experimental results of the shielding properties.

A Large Scale High-Tc Superconducting Shield and Its Cryostat

We have developed a cryostat for a large scale high-Tc superconducting shield enclosing a human body to measure biomagnetism. The cryostat has an interior space of ϕ 0.8 m × L2.8 m and cools a high-Tc superconducting shield ϕ 0.87 m × L2.4 m. The cryostat is made of non-magnetic materials to avoid internal magnetic noise. It also includes other provisions to achieve a very low magnetic noise environment. We investigated the optimal design of the radiation shields for the cryostats using liquid nitrogen and concluded that the one radiation shield has sufficient performance for the thermal insulation. We designed the liquid nitrogen reservoir to keep the superconductor at 77.3 K until the reservoir is nearly emptied.

High Sensitivity SQUID Damage Detector in a High-Tc Superconducting Shield

A non-destructive evaluation (NDE) system for material damages of metals has been developed. The system enables very low magnetic field measurements by using a SQUID magnetometry system in a high-Tc superconducting shield. The shield has large internal dimensions of D0.87 m × L2.4 m, so that large specimen of up to 50 cm × 10 cm can be inspected. Size and location of magnetization from various material damages were contact less estimated with a Nb-based multi-channel SQUID magnetometer system which was placed directly in the shield.

Material Damage Detector Using Squid Magnetometry

A SQUID magnetometry system using high Tc superconducting technology is developed to open up its applicability to nondestructive evaliation(NDE) on material damages of metals. And damages of austenitic stainless steels by plastic strain are successfully detected.

Relaxation in High Transport Current Bi-Sr-Ca-Cu-O System

The relaxation of a persistent current circulating in a toroid made of Bi2Sr2Ca1Cu2O8+x superconductor has been measured. The relaxation is described of the form of t-a and is explained by a equation deduced from a power-law characteristic of the I–V property, which is originated from a 2-dimensional coupled Josephson junction array. It is further revealed that the power-law can be applied to the superconductors over very wide ranges of voltages from 0.1mV to 0.1pV.

High Tc Superconducting Shielded Biomagnetometer System

Superconductors are expected to achieve perfect magnetic shielding, which will be useful for studies on neural activities of the brain especially in the lower frequency range down to DC. Operating in the environment of other noisy instruments and/or interference such as subways, cars, etc. will be available. Instead of gradiometers, higher sensitivity magnetometers are effective in the low noise space, which will allow detections of signals from deeper and/or weaker magnetic sources with a higher S/N ratio.