Screening of electromagnetic fields by particulate superconductors

This paper reports a series of experiments carried out to investigate the ability of a sintered tile of YBa2Cu3O7 to screen an applied low-frequency AC magnetic field superimposed on a stronger DC field. The results suggest that screening may be considered to have two regimes: For applied fields below 4 mT intergrain currents allow the tile to behave as an homogeneous sheet. When the total field is much greater than this, intergrain currents are suppressed and the sheet behaves as an array of isolated particles with a characteristic screening factor