[转帖]Scientists Say Invisibility Is Possible

badan · 发表于 2006-5-30 21:23:00

From Sci-Tech Today
Generally, Invisibility can be achieved by using the special material with negative refractive index , which is much different from common positive refractive index material. The light can "pass through" the object made by or covered by this material, as water would flow around a rock in a stream-- making the object appear to vanish.

Scientists Say Invisibility Is Possible
By Barry Levine
May 26, 2006 2:35PM

"If it ever became a consumer product, it would be incredible," said Jackie Fenn, an analyst at Gartner, a technology research firm. "But it's a materials science and mathematical theory at this point, and, given that it's at a fundamental state, it could be decades before we see -- or, rather, not see -- anything."

Like flying or living forever, invisibility has been a dream as long as humans have had imaginations. Harry Potter's cloak, cloaking devices in "Star Trek," H.G. Wells' "The Invisible Man," and even Plato's Ring of Gyges have embodied the imperceptible ideal. But now it looks like invisibility might be ready to move from the realm of fiction to the world of fact.

Two teams of scientists have separately reported in today's journal "Science" that new kinds of light-refracting "metamaterials" could theoretically bend light and make objects -- or individuals -- within those materials appear invisible.

Harry Potter fans looking to knit cloaks of their own will need to find other raw materials. The metamaterials the scientists describe are hardened -- more like a shield than soft fabric.

Refractive Index

As the scientists desribe them, these metamaterials are composed of tiny rods and metal rings. They are unusual in that they have a negative refractive index, meaning that they can treat electromagnetic radiation -- such as radar or visible light -- in ways that are different from normal materials. By adjusting their molecular structure, these properties can be tuned for given wavelengths and desired paths.

Refraction is the commonly observed phenomenon of, say, a pencil appearing to be bent when in a glass of water. When tuned appropriately, metamaterials could theoretically be made to bend given wavelengths around an object hidden within them, as water would flow around a rock in a stream -- making the object appear to vanish.

In their paper in today's journal "Science," physicist John Pendry of Imperial College London, along with David Smith and David Schurig, of Duke University, have shown theoretically how these metamaterials could be tuned so that light flows around a hole.

The same idea was presented in an independent study -- also in today's "Science" -- by Ulf Leonhardt, a physicist at the University of St. Andrews in Scotland.

Early Prototype?

Pendry predicted that demonstrating metamaterials that make an object invisible to radar -- not visible light -- might be possible within 18 months. Other scientists suggest it might be within five years.

This kind of radar invisibility would be different from, say, stealth technology in which radar is being prevented from reflecting back to its source. Duke's Shurig has noted that making metamaterials work for the entire visible spectrum would be a much greater task.

Observers of emerging technologies caution about such metamaterials reaching the marketplace for general consumer use. "If it ever became a consumer product, it would be incredible," said Jackie Fenn, an analyst at Gartner, a technology research firm. "But it's a materials science and mathematical theory at this point, and, given that it's at a fundamental state, it could be decades before we see -- or, rather, not see -- anything."

But, like any superpower endowed on mere mortals, this kind of invisibility works both ways. Any person inside such materials would need to use a specific, excluded frequency -- for example, infrared -- in order to see out.

乏味 · 发表于 2006-5-31 20:44:00

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[转帖]Scientists Say Invisibility Is Possible

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