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Enhanced Cloaking Device Eliminates Reflections

DURHAM, N.C., Nov. 12, 2012 — A new technology refines the original invisibility cloak by eliminating the reflections at the edges of the device that result in lost waves — one of the key issues preventing complete invisibility. The enhanced metamaterial could revolutionize lightwave transmission.

When the Duke University team first developed a cloaking device in 2006, it worked, but had minor reflections along the edges and corners of the spaces within and around the metamaterial — a man-made object that has properties often absent in natural ones.

“In order to create the first cloaks, many approximations had to be made in order to fabricate the intricate metamaterials used in the device,” said Nathan Landy, a graduate student working with senior investigator David R. Smith at the Pratt School of Engineering. “One issue, which we were fully aware of, was loss of the waves due to reflections at the boundaries of the device.”


Duke University graduate student Nathan Landy with the cloaking device. Courtesy of Duke University Photography.

After successfully demonstrating the basic cloaking principles, the team turned its attention to reducing these reflections and improving the completeness of the cloaking effect.

The original device was composed of fiberglass strips etched with copper and arranged in a parallel and intersecting pattern. Using a similar row-by-row design, Landy’s new cloak added copper strips that create a more complicated, yet better performing, material that guides lightwaves around the object. The strips of the device form a diamond shape, with the center left empty. The device is about 2 x 2 ft.

The cloak, naturally divided into four quadrants, was designed to counteract the reflections, or blind spots. “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 said. “We built the cloak, and it worked. 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.”

The approach could have applications other than cloaks, he said. For example, metamaterials can “smooth out” twists and turns in fiber optics, making them seem straighter. This is important because each bend attenuates the wave within it, he said.

The researchers are now working to apply the principles learned in the latest experiments to three-dimensional technology — much more difficult than working in two dimensions.

The study appeared in Nature Materials (doi: 10.1038/nmat3476). 

For more information, visit: www.duke.edu

For more invisibility cloak research from Duke University, see: Theoretical Blueprint for Invisibility Cloak Reported, Cloak of Partial Invisibility Created, and Technology: Making Invisibility Cloaks Real with Metamaterials


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