The results of shielding characteristics measurements of superconducti
ng shields in the form of hollow cylinders based on YBa2Cu3O7 high-T(c
) superconducting ceramics are reported. Shields provided ac shielding
coefficient up to 72 dB at 89 K. It was shown that spectrum analysis
of magnetic flux inside cylindrical shield can be a tool to distinguis
h a mechanisms of field penetration into shielded volume.