Scientists in the US say they are a step closer to developing materials that could render objects, including people, invisible. Researchers at the University of California, Berkeley have developed two new types of materials that can bend light the wrong way, creating the first step toward an invisibility cloaking device. One approach uses a type of fishnet of metal layers to reverse the direction of light, while another uses tiny silver wires, both at the nanoscale level. Both are so-called metamaterials – artificially engineered structures that have properties not seen in nature, such as negative refractive index. Two teams of Berkeley scientists working under the direction of Xiang Zhang reported their findings in the journals Science, and Nature. “In naturally occurring material, the index of refraction, a measure of how light bends in a medium, is positive,” said Jason Valentine, one of the scientists. “When you see a fish in the water, the fish will appear to be in front of the position it really is. Or if you put a stick in the water, the stick seems to bend away from you.” These are illusions caused by the light bending when it moves between water and air. The negative refraction achieved by the teams at Berkeley would be different. “Instead of the fish appearing to be slightly ahead of where it is in the water, it would actually appear to be above the water's surface,” Valentine said. “It's kind of weird.” The new system works like water flowing around a rock, the researchers said. Because light is not absorbed or reflected by the object, a person only sees the light from behind it - rendering the object invisible. The team says the principles could one day be scaled up to make invisibility cloaks large enough to hide people. The research could also one day be used in military stealth operations - with tanks made to disappear from the enemies' sight.
