The reason is that, to produce the cloaking effect, the substructures of the metamaterials must be smaller than the wavelength of light being redirected. That’s currently feasible for microwaves, which have a wavelength of about three centimeters. But redirecting visible light, which has a wavelength of around half a micrometer, or half a millionth of a meter, would require metamaterials with structures engineered at the molecular level. “We would like to do it on a molecular scale, but nanoengineering is not yet up to it,” says Pendry. Recent developments in nano metamaterials, however, could speed the development process up.
For now, then, the prototype cloak consists of arrays of millimeter-sized copper rods and C-shaped rings embedded in a composite fiber board, much like the kind of printed circuit boards that normally house computer chips. Both the rods and the C-rings are capable of passively creating electromagnetic fields when exposed to microwave radiation. When oriented just right, these components can specify the path that the radiation will follow.
There is also another application for cloaking, says Schurig: it can be used as a kind of shield. “Sometimes you want to protect or isolate things from the electromagnetic spectrum,” he says. For example, cloaking could be used on space probes to protect sensitive equipment from cosmic radiation.
But there is a catch. While any cloaked object would be invisible, it would also be blind within the cloaked frequency range, since any light directed toward it would be rerouted around it. In the case of a radar-cloaked plane, this should not be a major problem, says Schurig. The pilot would be unable to use radar, but she could still navigate visually.