Electromagnetic metamaterials are artificially structured materials that are designed to interact with and control electromagnetic waves. Electromagnetic waves might be any type of wave in the electromagnetic spectrum (shown here on the figure to the right). Most of us are familiar with light waves in the visible, which occupy a rather small portion of the electromagnetic spectrum. Visible light waves have wavelengths from 400 to 700 nanometers (a nanometer is one-billionth of a meter), yet electromagnetic waves can have wavelengths of thousands of kilometers to trillionths of a meter!
When light (or electromagnetic) waves enter a material, the electric and magnetic fields of the wave cause electrons within the material to move around. This exchange of electromagnetic energy with the atoms and molecules of a material is the means by which materials can be used to control and manipulate light waves, forming the basis for electromagnetic devices.
The size and typical spacing of atoms within a material are on the order of angstroms, or tenths of one nanometer. That means that visible light waves, which are hundreds of nanometers in size, or longer wavelength waves cannot even come close to resolving the atomic structure. Although we know materials are formed from collections of atoms, we cannot see the individual atoms because the light we perceive is so much larger than the atomic scale. So, we are able to approximate the discrete atoms and molecules of a material as a continuous substance, whose properties derive not only from the individual atoms and molecules, but also their interactions.