Two-Scale limit of the solution to a Robin Problem in Perforated Media

The two scale convergence of the solution to a Robin's type-like problem of a stationary diffusion problem in a periodically perforated domain is investigated. It is shown that the Robin's problem converges to a problem associated to a new operator which is the sum of a standard homogenized operator plus an extra first order "strange" term; its appearance is due to the non-symmetry of the diffusion matrix and to the non rescaled resistivity.