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Brazilian Physicists Theorize On the Perfect "Invisibility Cloak"

01/10/2014 - 08h24

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SALVADOR NOGUEIRA
REPORTS FOR FOLHA

Forget about Harry Potter. Research conducted by a group of Brazilian physicists has proposed the means of obtaining the perfect "invisibility cloak."

The research, published in the scientific journal "Physical Review Letters", suggests that not only will it be possible to create a material which renders an object invisible, but it will also be possible to "tune" this material so that it can be used in diverse frequencies of light.

The notion of such a device has been part of the human imagination since at least Ancient Greece. However, until just a few years ago, invisibility was seen as impractical.

To hide a spaceship beneath camouflage as seen in Star Trek, would require, in theory, curving the space around the vehicle so that light does not touch it. The energy required by such a procedure would be so high as to make it virtually impossible.

But there is a much more simple solution, which was proposed for the first time in 2006.

Instead of using brute force to curve space around an object, researchers suggested that it would be possible to use artificially projected materials (metamaterials), which have a property known as a negative refractive index. These materials would coat the object which is to be hidden.

From here, there are two ways of producing invisibility: the first involves covering the object in a metamaterial that repels light around it, rendering the object invisible. The other, rather than repelling the light, would reflect light waves in such a way as to cancel them out.

Both methods are potentially viable, but they come with a problem: the metamaterial would produce invisibility only at a given, specific frequency. For example, an invisibility cloak that successful hid an object in infrared light would be no use in visible light.

This is where the Brazilian researchers come in. Wilton Kort-Kamp, Felipe Rosa, Felipe Pinheiro and Carlos Farina, from the Federal University of Rio de Janeiro (UFRJ), suggest that it is possible to create an invisibility cloak using second method, while tuning the metamaterial to different light frequencies.

An external magnetic field would regulate which light frequency has to be cancelled, meaning that the object would be virtually impossible to detect.

The group's work suggests that this solution could work, even using metamaterials already in existence. However, they are theoretical physicists, and do not intend to put theory into practice.

"So far no other group has made contact with us to try out our theory," says Felipe Pinheiro, one of the authors of the study.

The group is currently investigating theoretical aspects of effects that may be produced by invisibility devices. The focus of the work, however, is theoretical rather than practical.

Translated by TOM GATEHOUSE

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