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Duke University engineers build a better invisibility cloak

From the philosophical discussion of the Ring of Gyges in Plato's Republic, to Sauron's One Ring in Lord of the Rings, Harry Potter's cloak of invisibility, and the 'cloaking devices' of the Klingons and Romulans in Star Trek, invisibility has long been in our fiction. In 2006 a group of Duke University researchers made invisibility a reality, however the system wasn't perfect.

Now, Dave Smith, the man behind the first successes, is co-authoring a study with graduate student Nathan Landy about their use of 'metamaterials' — artificial composites that can be made to interact with electromagnetic waves in ways that natural materials cannot reproduce — and the field of transformational optics, to 'perfect' the invisibility process.

"In order to create the first cloaks, many approximations had to be made in order to fabricate the intricate meta-materials used in the device. One issue, which we were fully aware of, was loss of the waves due to reflections at the boundaries of the device," Landy said, referring to how one can see through a pane of glass, but at the same time is aware of the glass due to reflections on the glass surface.

"Since the goal was to demonstrate the basic principles of cloaking, we didn't worry about these reflections," he added.

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The original design of the cloak involved concentric circles of fibreglass strips that were etched with copper. Light encountering the surface of the cloak is transmitted around the exterior of the cloak to emerge on the other side, thus concealing the cloak itself and the interior from view. The cloak was divided into four sections, and according to Landy, it was the edges of the four sections, and the spaces between them, that showed the most reflections.

"Each quadrant of the cloak tended to have voids, or blind spots, at their intersections and corners with each other," said Landy. "After many calculations, we thought we could correct this situation by shifting each strip so that it met its mirror image at each interface."

Landy's new design incorporates copper strips and restructures the cloak into more complex diamond shape.

"We built the cloak, and it worked," he said. "It split light into two waves which traveled around an object in the center and re-emerged as the single wave with minimal loss due to reflections."

Landy says that invisibility isn't the only application of their research. This can improve fibre optic transmissions, smoothing out turns and kinks in the lines, effectively making them straight.

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The next challenge of the research will be to move from 2-dimensions to 3-dimensions.