Mystery of the double limit in homogenization of finitely or perfectly conducting periodic structures.

We show that the difference in the effective medium properties of perfectly or finitely conducting short-period gratings is because for finitely conducting gratings it is possible to completely homogenize the electromagnetic field vector components, contrary to perfectly conducting gratings. As a consequence, for aluminum in the microwave domain, two possible effective media can be found, depending on whether the feature dimensions are much larger or shorter than the depth of field penetration inside the metal.