  An important tool in the field of metamaterials is the extraction of
effective material parameters from simulated or measured scattering parameters
of a sample. Here we discuss a retrieval method for thin-film structures that
can be approximated by a two-dimensional scattering sheet. We determine the
effective sheet conductivity from the scattering parameters and we point out
the importance of the magnetic sheet current to avoid an overdetermined
inversion problem. Subsequently, we present two applications of the sheet
retrieval method. First, we determine the effective sheet conductivity of thin
silver films and we compare the resulting conductivities with the sheet
conductivity of graphene. Second, we apply the method to a cut-wire
metamaterial with an electric dipole resonance. The method is valid for
thin-film structures such as two-dimensional metamaterials and
frequency-selective surfaces and can be easily generalized for anisotropic or
chiral media.
