Metamaterials are specially-engineered materials that possess properties not found in nature. Often utilising nanotechnology to create the given object, the combination of the material's shape, geometry, size, orientation and arrangements give them their unique properties.
The most common application is in electromagnetic metamaterials that can alter their properties to be entirely transparent or opaque to EM radiation, or even to redirect it. In this instance, a given item or surface is composed of countless nano-scale cells that channel different wavelengths of EM radiation based on the cell's size. To deal with a range of wavelengths, a metamaterial sample can be composed of a variety of differently-sized cells, or incorporate means by which the cells can change in size, such as through nanotechnology or piezoelectrics.