Cloak of Invisibility

[Alram]

Now you see it, now you don't: cloaking device is not just sci-fi

Ian Sample, science correspondent
Wednesday May 3, 2006
The Guardian

It's been the curse of the USS Enterprise and the Klingons' favoured weapon. But back on Earth, mathematicians claim to have worked out how to make a cloaking device to render objects invisible.

An outline for the device is described in a scientific paper published today in which the authors reveal how objects placed close to a material called a superlens appear to vanish.

Even in the world of science fiction, the technology is not perfect, and nor is the device proposed by Graeme Milton at Utah University and Nicolae-Alexandru Nicorovici at Sydney University of Technology. According to their calculations, the device would only work at certain frequencies of light, and only if the object is within close range of the superlens.

The cloaking device relies on recently discovered materials used to make superlenses that make light behave in a highly unusual way. Instead of having a positive refractive index - the property which makes light bend as it passes through a prism or water - the materials have a negative refractive index, which effectively makes light travel backwards. It's light, but not as we know it.

Prof Milton's team calculated that when certain objects are placed next to superlenses, the light bouncing off them is essentially erased by light reflecting off the superlens, making the object invisible.

The calculations show that while the device could be used to obscure almost any shape of object, it only works over a short range of wavelengths, so if used to hide objects from human vision, they might only partially disappear.

Sir John Pendry, a theoretical physicist at Imperial College London who invented superlenses, said: "Effectively, they are making a piece of space seem to disappear, at least as far as light is concerned."

The research appears in the journal Proceedings of the Royal Society today.

Prof Pendry said the technology has great potential for hiding objects from radar or cloaking electronic instruments so they can be used in strong electromagnetic fields, such as those produced by hospital MRI brain scanners. "The secret is having the cloak itself be invisible and if you can do that cheaply and efficiently and it doesn't need to be metres thick, it would be extremely valuable for stealth. Even if you could cloak a single frequency, it would be very useful. The military is extremely interested in this."

So far the researchers have only worked through the mathematics to prove that the device is plausible. The practicalities of making one have yet to be solved.

Guardian