Silicon Carpet Invisibility Cloak

Tiny Invisibility Cloak Constructed

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Kristy Erdodi / DailyTech

May 04, 2009

‘A tiny invisibility cloak has been developed, combining silicon and a carpet-like design.’ -

A tiny, unique cloak has been developed, demonstrating how silicon and a carpet-like design can take scientists even further in their explorations of invisibility.

The journal Nature Materials reported on the development, which was constructed based on a carpet-like design theory first described by Professor John Pendry, from Imperial College London, in 2008. Teams involved in its current production included Michal Lipson and her team at Cornell University and Xiang Zhang, along with his team at University of California, Berkeley.

Hosting a design that allows it to eliminate distortion from the shape of anything underneath it, the cloak enables light to bend around it, which creates the illusion of a flattened surface.

A silicon sheet measuring a few thousandths of a millimeter across and containing multiple miniature holes makes up the cloak, which “changes the local density” of the item placed beneath it, according to Professor Zhang.

“When light passes from air into water it will be bent, because the optical density, or refraction index, of the water is different to air,” Professor Zhang explained. “So by manipulating the optical density of an object, you can transform the light path from a straight line to any path you want.”

The key to changing the optical density in this case lies in the cloak’s holes, which optical light cannot see because they are smaller than the size of its wavelength. All optical light does see is a “sort of air-silicon mixture,” as Professor Zhang explained, which means that at least in terms of light’s view, the item’s density has been altered.

The recently constructed silicon sheet does not stand as the first attempt at invisibility through a cloak. For example, in early August of 2008, Researchers at the Nanoscale Science and Engineering Center at the University of California, Berkeley used nano-fishnet of metal layers and nanoscale silver wires to cloak 3D materials. The two separate teams involved in this project, which also relied on the bending of light, were led by Professor Zhang, as well.

Similar attempts at invisibility cloaks of the past have also included constructions made of metal, which highlights this current project’s significant step toward progression. Unlike metal, which allows for losses of light, silicon absorbs only a minimal amount. The new material enables scientists to move forward from some of the flaws that metal’s light loss can cause upon trying to achieve invisibility.

© 2009, DailyTech