Science reveals secrets of invisibility

Source : http://www.cnn.com/2006/TECH/science/08/09/feature.invisibility/index.html

(CNN) -- Invisibility has long been a fantastical ability exclusively enjoyed by teenage wizards, super heroes and the ultra-advanced civilisations of science fiction.

But more pragmatic-minded scientists and engineers now believe that invisibility-enabling technology may be within reach of lesser mortals as well.

The key to that possibility is the development of increasingly complex metamaterials -- manmade composites engineered on a nano scale with properties entirely different to anything found in nature.

Doctor Ulf Leonhardt, a physicist at Scotland's St. Andrews University who has recently published two papers on the theory behind invisibility technology, said the key was developing a transparent material capable of bending light around an object concealed behind it.

"What you want to do is to surround yourself with a transparent material that is not only transparent but bends the light around you," Leonhardt told CNN.

Leonhardt said the underlying principle was inspired by natural phenomena when light is bent to create optical illusions such as the refraction of a spoon in water or a mirage in the desert or on hot tarmac.

"There are many examples of ways a transparent material like water glass or air can bend light," said Leonhardt. "The reason that is possible is because light will always take the shortest route, which is not always a straight line. All you need is a transparent material that bends light around an object like water moving around a stone."

Work on metamaterials that could ultimately make invisibility a reality is already underway at Duke University in the U.S., where a team led by Professor David R. Smith is experimenting with the design of materials to shield objects from other electromagnetic waves such as microwaves.

Leonhardt said that once that technology had been developed it would merely need to be replicated on a smaller scale to work for light waves as well.

"The essential idea is that all you have to do is make things smaller. Visible light has a significantly smaller wavelength than microwaves or radio waves but you could take the same building blocks and make them very small. Thanks to nanotechnology there is a chance that can be done."

One problem that engineers would face would be in creating a metamaterial covering the full range of the optical spectrum rather than a single color or light frequency. Currently researchers are only working on developing materials with the ability to channel waves of a specific frequency.

But Leonhardt said he believed the issue was surmountable: "There will be advances on both the technological and theoretical sides which will make invisibility happen in the not too distant future. This is not completely beyond the range of present technology and theoretical ideas."

While there may ultimately be practical, ethical and security considerations to be considered for invisibility technology, initial applications are likely to focus on microwave shielding, protecting electrical devices from electromagnetic interference, and applications to enable more effective wireless communications, Leonhardt said.

"What these new ideas give you is a new set of tools to guide microwave radiation in a controlled and precisely adjusted way. Generally anything connected with wireless technology would benefit from these new design ideas."

Ironically, the method by which invisibility might be achieved is not dissimilar to the way in which one comic book hero already achieves her special powers. The Invisible Woman, one of Marvel's "Fantastic Four," hides behind a forcefield which guides light around her.

"This really is the underlying principle of these devices. You mimic with a material an effect that would occur with a field like a curved space," said Leonhardt. "That's the closest example to what people could perhaps do with modern technology."

But the Invisible Woman and Harry Potter, armed with his invisibility cloak, may still have an advantage over anything technology is capable of. In the real world, anything or anyone concealed from view would also be trapped in darkness.

"You would see black, of course ," said Leonhardt. "You are completely cut off from light as it is guided around you -- so you wouldn't see anything."

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Thats obvious, We see the objects because light falling on it reflects and falls on our retina. The particular color reflects respective wavelength's light. If we cover ourself with a transparent sheet which doesn't reflect any light nor it absorbs, instead it should guide it(the example they have given is water guiding on the surface of a rock). The day isn't too far when we'll get to see such costumes.