The magnetic shielding effect of Ba2YCu3O7-δ, Cu and Fe-Ni plates was examined as a function of the frequency of applied ac magnetic field using magnetic heads. The effect of Ba2YCu3O7-δ plates was superior to that of Cu and Fe-Ni plates in the low-frequency ( 10 kHz) region, the effect of Ba2YCu3O7-δ plates was almost the same or slightly inferior to that of Cu plates. The shielding effect of Ba2YCu3O7-δ plates was strongly affected by the micro cracks and porosity of the samples. The magnetic shielding effect of Ba2YCu3O7-δ plates decreased rapidly with applied dc magnetic field, while the effect of Cu and Fe-Ni plates did not change with the application of dc magnetic field.

https://iopscience.iop.org/article/10.1143/JJAP.29.2403/pdf

Magnetic Shielding Effect of Ba2YCu3O7-δ Plates

Magnetic shielding effects of superconducting Y-Ba-Cu-O vessels have been studied. Magnetic fields inside a Y-Ba-Cu-O vessel in a superconducting state at 77 K were compared with those in a normal state at 290 K by measuring induced voltages in a pick-up coil inside the vessel. The ratio of the magnetic field at 77 K to that at 290 K was as good as 2×10-6 when a magnetic field of 0.03 mT at 1000 Hz was applied to the outside of the vessel. This attenuation ratio is good enough for neuromagnetic measurements with a SQUID magnetometer.

Magnetic Shield of High- T c Oxide Superconductors at 77 K

Plasma sprayed high Tc superconducting magnetic shields

Preliminary results of measurements performed on two bulk MgB2 cylinders intended for use as toroidal magnetic shields with a novel cryogenic current comparator are reported up to 37 K, showing an attenuation factor greater than 106 at 27 K, lowering by a factor of 10 at 34 K.

https://iopscience.iop.org/article/10.1088/0953-2048/20/7/L01/pdf

An MgB2 superconducting shield for a cryogenic current comparator working up to 34 K

Studies of the propagation of an AC magnetic field through plasma sprayed superconducting Y1Ba2Cu3O7-x coatings have been carried out in the incident field frequency and intensity ranges 100 Hz to 100 kHz and 0.01 to 3.5 mT respectively. Results show that the shielding effectiveness increases exponentially with decreasing field intensity. Shielding effectiveness increases with coating thickness and its density. Coatings thinner than 100 mu m do not show any shielding. A non-linear dependence of critical magnetic field H* on both thickness and critical current density Jc of the specimen has been observed.

Study of the propagation of an AC magnetic field through superconducting thick films

The magnetic shielding has been investigated by measuring magnetic coupling between primary and secondary coils separated by a high-Tc superconductor. The magnetic coupling between primary and secondary coils could not be zero below Tc. This can be explained by the existence of superconductivity related surface current, which flows out from front to rear surface to couple with the secondary coil.

Shigeyasu Kanazawa

Papers

Magnetic shielding using high-Tcsuperconductor