Defining Metamaterials and Their Unnatural Properties
The Defense Intelligence Agency's Act request to The Black Vault, opens with a precise definition that sets the stage for its technical survey. A metamaterial, as the record states, is an artificial medium whose properties—mechanical, optical, magnetic, or otherwise—cannot be found in naturally occurring materials. The document's emphasis is on electromagnetic and optical metamaterials, which can exhibit extreme characteristics such as a negative refractive index.
This phenomenon requires both electric permittivity and magnetic permeability to be negative, a condition not observed in nature. Historically, such materials were termed 'left-handed' due to the unusual phase relationship between electric and magnetic fields; in conventional media, the right-hand rule governs the relationship among the electric field, magnetic field, and propagation wavenumber, with the Poynting vector and phase velocity aligned. In negative-index metamaterials, these directions are opposite, necessitating a left-handed relationship.
The designation fell out of favor because it caused confusion with chiral structures,…