Several characters in fiction and myth, including Harry Potter, King Arthur and the Japanese hero Momotarō, have owned cloaks of invisibility. Fiction might soon become reality, as researchers are finding ways to manipulate light using metamaterials — artificial materials with complex structures and unusual optical properties.
In 2006 a group at Imperial College, London, gave the first practical demonstration of an invisibility cloak. They used a flexible three-dimensional lattice of identical electronic elements to direct microwaves around an object so that it seemed not to be there. To produce ‘invisibility’, the lattice spacing must be similar to the radiation wavelength, and metamaterials on a microwave scale can be manufactured using 3D printing (Figure 1). The challenge is to make nanoscale metamaterials that produce invisibilty with light. This might involve using negative index materials (NIMs — Figure 2).
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