Coils are placed coaxially on either side of a slab of superconductor of thickness 0.05-1 mm. The coil diameters are less than the lateral dimentions of the slab. The voltage in the secondary coil is measured as a function of excitation current and frequency in the primary, and of the temperature and the steady magnetic field provided by an external solenoid. A YBa2Cu3O7 ceramic cooled in zero field screens almost completely, but the greater part of this screening is suppressed by low magnetic fields. The remaining part is shown to be due to isolated superconducting grains. When intergrain superconductivity is partly suppressed the condition is reasonably well described by the Bean critical-state model. Hysteresis of the screening coefficient reflects the known hysteresis of the transport critical current.

AC screening measurement for the characterization of oxide superconductors: I. Application to ceramics

High temperature superconducting materials (HTS) offer several advantages in magnetic field shielding applications. HTS materials have the potential of creating efficient shields by reducing the size and weight of the shielding systems. The main limitation until recently has been the difficulty of producing HTS tapes of large width. Recent developments in second-generation (2G) high temperature YBCO superconductors allow the production of 2G films on very large 4 cm wide substrates. Magnetic field shielding properties of coils and sheets fabricated from 4 cm wide YBa2Cu3O7-coated conductors are reported. Shielding properties of shields with multiple layers were measured at liquid nitrogen temperatures. Magnetic field amplitude inside the superconducting shields was measured using Hall probes with a phase-sensitive technique. Efficacy of the shields was characterized at varying field amplitude and frequency. Shielding of up to 95% of applied magnetic field was observed at magnetic field amplitudes of <10 mT. The frequency dependence of shielding properties depended on the geometry of the shields.

https://iopscience.iop.org/article/10.1088/0953-2048/22/12/125009/pdf

Shielding AC magnetic fields using commercial YBa2Cu3O7-coated conductor tapes

Magnetic field shielding properties of coils and sheets of silver sheathed (Bi,Pb)2Sr2Ca2Cu3O10+x tapes (1G superconductor tapes) and YBa2Cu3O7 coated conductors (2G superconductor tapes) are reported. Shielding properties were measured at 77 K, with varying field amplitude and frequency of external magnetic field, using Hall probes and a phase sensitive technique. Shielding factor data on several coils and sheets are presented as a function of external field amplitude and frequency. Magnetic field shielding of up to 50% was observed at field amplitudes of < 10 mT. Differences in frequency dependence of shielding properties of test shields fabricated from 1G and 2G conductors are discussed.

Shielding of AC Magnetic Fields by Coils and Sheets of Superconducting Tapes

Magnetic measurements in the superconducting state of the high temperature superconductors have been characterized by the feature of irreversibility. Similar effects have been known in the conventional type II superconductors for about three decades now, and have been studied in great detail during the last few years. Recent studies of magnetic irreversibilities, in both conventional and high temperature superconductors, will be reviewed here. Thermally-activated relaxation accompanies such irreversibilities, and studies on flux-creep will also be reviewed.

Studies of irreversible magnetization in superconductors - a review

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

Plasma sprayed high Tc superconducting magnetic shields

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.

Electromagnetic shielding studies on plasma‐sprayed superconducting high-TC coatings

Studies on the propagation of AC magnetic field through plasma-sprayed superconducting Y1Ba2Cu3O7−x
 coatings show that complete shielding is achieved up to a certain critical magnetic field strengthH
 0. Increase in the thickness orJ
 c
 of the specimen increases theH
 0 value. Flux-trapping occurs in the specimen at high frequencies and the frequency at which it occurs increases with increase in specimenJ
 c
 .

/pdf/propagation-of-a-c-magnetic-field-through-high-t-c-coatings-popc5f7umf.pdf

A. S. Paithankar

Papers

Plasma sprayed high Tc superconducting magnetic shields

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

Electromagnetic shielding studies on plasma‐sprayed superconducting high-TC coatings

Propagation of a.c. magnetic field through high-T c coatings