  The distribution of ac magnetic fields in a thin superconducting strip is
calculated when an ac current is applied to the sample. The edge barrier of the
strip to flux penetration and exit is taken into account. The obtained formulas
provide a basis to extract voltage-current characteristics in the bulk and at
the edges of superconductors from the measured ac magnetic fields. Based on
these results, we explain the spatial and temperature dependences of the
profiles of the ac magnetic field measured in a Bi2Sr2CaCu2O8 strip [D.T. Fuchs
et al., Nature 91, 373 (1998)].
