  To study the scattering properties of metamaterials, we generalize two
scattering methods developed for conventional (non-magnetic) isotropic
materials to the case of materials with arbitrary values (positive or negative)
of magnetic permeability and electric permittivity. The generalized methods are
used to study the changes in the reflectivity of a metamaterial surface with
localized roughness when the relative refractive index changes sign. Our
results show that, unlike the case of a plane surface whose reflectivity is
unaffected by the change of sign of the relative refractive index, in rough
surfaces the change of sign is manifested in the reflectivity, even for very
low roughness, particularly in observation directions away from the specular
direction.
