Metamaterials, a challenge for homogenization theory

Metamaterials are crystal-like composites, derived by spatial translations from a generating cell, where highfrequency electromagnetic fields propagate in surprising ways at some frequencies: Negative refraction, "bending light the wrong way", refocusing of divergent beams into tightly parallel ones, are observed, and attributed to the fact that, at a spatial scale higher than the cell size, the composite behaves as a homogeneous material, but one with "emerging" properties, not possessed by any of the components.