单选题
Marvelous Metamaterials
Invisibility cloaks would have remained impossible, forever locked in science fiction, had it not been for the development of metamaterials. In Greek, "meta" means beyond, and metamaterials can do things beyond what we see in the natural world-like shuffle light waves around an object, and then bring' them back together. If scientists ever manage to build a full-fledged invisibility cloak, it will probably be made of metamaterials.
"We are creating materials that don't exist in nature, and that have a physical phenomenon that doesn't exist in nature," says engineer Dentcho Genov. "That is the most exciting thing." Genov designs and builds metamaterials such as those used in cloaking at Louisiana Tech University in Ruston, Louisiana.
An invisibility cloak will probably not be the first major accomplishment to come from the field of metamaterials. Other applications are just as exciting. In many labs, for example, scientists are working on building a hyperlens. A lens is a device, usually made of glass that can change the direction of light waves. Lenses are used in microscopes and cameras to focus light, thus allowing a researcher to see small things or a photographer to capture image of things that are far away.
A hyperlens, however, would be made of metamaterials. And since metamaterials can do things with light that ordinary materials can't, the hyperlens would be a powerful too 1. A hyperlens would allow researchers to see things at the smallest scale imaginable, as small as the wavelength of visible light.
Genov points out that the science of metamaterials is driven by the imagination. If someone can think of an idea for a new behavior for fight, then the engineers can find a way to design a device using metamaterials. "We need people who can imagine," he says.
Since 2006, many laboratories have been exploring other kinds of metamaterials that don't involve just visible light. In fact, scientists are finding that almost any kind of wave may respond to metamaterials.
At the Polytechnic University of Valencia in Spain, Jose Sanchez-Dehesa is working with acoustics, or the science of sound. Just as an invisibility cloak shuffles waves of light, an "acoustic" cloak would shuffle waves of sound in a way that's not found in nature. In an orchestra hall, for example, an acoustic cloak could redirect the sound waves so someone sitting behind a column would hear the same concert as the rest of the audience without distortion.
Sanchez-Dehesa, an engineer, recently showed that it's possible to build such an acoustic cloak, though he doubts we'll see one any time soon. "In principle, it is possible," he says, "but it might be impossible to make one." he adds.
Other scientists are looking into ways to use larger metamaterials as shields around islands or oil rigs as protection from tsunamis. A tsunami is a giant destructive wave. The metamaterial would redirect the tsunami around the rig or island, and the wave would resume its energy on the other side without causing any harm.