Human-scale invisibility cloak unveiled


American scientists have unveiled how to make invisibility cloaks that are big enough to hide a human - or even a satellite orbiting the earth.

As the interest in creating Harry Potter-style cloaks continues to grow, researchers in America have shown how a simple trick used for years by magicians can create the desired effect, according to an article published in the latest issue of the MIT Technology Review journal.

Using conventional lenses and mirrors, the scientists are able to steer light around the region of space they want to hide, the article said.

It said: "In the last decade or so, invisibility cloaks have captured the imagination of researchers and the public alike. The excitement is based on two advances.

The first is the idea of "transformation optics," or the ability to bend light around a region of space to make it look as if it weren’t there. The second is the creation of metamaterials–synthetic substances with optical properties unknown in nature that can be designed to achieve this goal.

The article said: "One of the goals in this area is to create a Harry Potter-style cloak capable of hiding a human at all optical frequencies in all directions. A bonus would be the ability to make this device as big or small as required so that it can hide objects of any size — even ones as large as orbiting satellites, according to US researchers.

Achieving all these features in a single gadget is currently impossible. The first cloak worked only at a single microwave frequency. More recent cloaks operate over the entire a range of optical frequencies but can only hide tiny objects over a limited viewing angle.

In a paper published on June 5, John Howell at the University of Rochester in New York and Benjamin Howell show how to make simple cloaks that hide huge objects over the entire optical spectrum, albeit with a significant compromise. One of their devices is big enough to cloak a person.

Their approach is head-slappingly simple. Instead of using complex metamaterials to steer light, the Howells do the same job with conventional lenses and mirrors.

They simply create an array of lenses or mirrors that steer light around the region of space they want to hide."

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