Field distribution in granular, diamagnetic materials

Field distributions in samples composed of spherical, perfectly diamagnetic grains, randomly dispersed in a nonmagnetic matrix, are discussed on the basis of numerical calculations. Results of a spherical sample of 580 identical grains, which occupy 58% of the volume, show that (a) the dipole moment of the sample is in good agreement with effective medium theory predictions, (b) the superconducting volume fraction can be inferred from its measured dipole moment, and (c) the dipole part of the actual field, to which a grain in this spherical sample is exposed varies from 70% of the applied field (near the poles) to 130% (near the equator).<>