ABSTRACT
Optical properties of metamaterials are conceptually di˜erent from those of the natural materials. Most of these di˜erences can be traced back to the fact that the unit cell of a natural material is extremely small whereas that of most metamaterials is, generally, not. Œe relevant spatial scale to compare the unit cell’s size a of either natural material or metamaterial is the wavelength of light λ. Œe unit cell’s size of a natural material is only on the order of the Bohr’s radius aB ≈ 0.5 = 5 × 10-9 cm. Œerefore, it is four orders of magnitude smaller that the wavelength λ = 500 nm of the visible light in vacuum. One implication of that is the negligible phase shi¹ of a propagating electromagnetic (or optical) wave across the unit cell. Specižcally, this phase shi¹ φ pi λ= 2 1na/ unless the refractive index of the material n > 103. Such a refractive index would correspond to the dielectric permittivity e = n2 > 106. No such materials exist in nature.
