  As an example of thin composite layers we consider single and double grids of
periodically arranged interacting wires loaded with a certain distributed
reactive impedance. Currents induced to the wires by a normally incident plane
wave are rigorously calculated and the corresponding dipole moment densities
are determined. Using this data and the averaged fields we assign mesoscopic
material parameters for the proposed grid structures. These parameters depend
on the number of grids, and measure the averaged induced polarizations. It is
demonstrated that properly loaded double grids possess polarization response
that over some frequency range can be described by assigning negative values
for the mesoscopic parameters. Discussion is conducted on the physical
meaningfulness to assign such material parameters for thin composite slabs. The
results predicted by the proposed method for the double-grid structures are
compared with the results obtained using the commonly adopted S-parameter
retrieval procedure.
