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article imageFrom invisibility cloaks to magic carpets

By Aditi Chengappa     May 2, 2009 in Technology
After the recent breakthrough with invisibility cloaks, the next in line are magic carpets, well almost magic, these carpets can conceal objects by making bumps look flat.
In a report by Nature journal,
Xiang Zhang and his colleagues at the University of California, Berkeley, and Michal Lipson's team at Cornell University, Ithaca, New York have independently created different versions of the silicon carpet that masks objects at infrared wavelengths.
"In both designs, a mirrored edge that contains a bump appears flat, allowing an object to be tucked behind the bump without being seen. Infra-red light rays shone on the bump are bent by the surrounding material, making it appear that the radiation that bounces back has been reflected by a flat mirror."
"The disguised bumps are only around 3 micrometres across, says Thomas Zentgraf, a member of the Berkeley team — and the effect only works for light rays confined to run on a flat two-dimensional plane through the cloak, hitting the bump head-on. Given this proof of concept, however, larger bumps and even three-dimensional cloaking could be within reach. "It should be possible to make this work at visible light — it is just a question of device fabrication," Zhang says."
To create the appearance of empty space rather than flat mirrors, invisibility cloaks would have to rely on meta-materials, which are materials whose complex structure can steer light around objects. However such meta-materials have only worked at specific wavelengths.
"Last year, John Pendry of Imperial College London, together with Jensen Li ,now on Zhang's Berkeley team, put forward the idea of a cloaking carpet, which would, in theory, be easier to make. By January 2009, David Smith of Duke University, North Carolina, had published a version of the carpet that worked at a broad band of microwave frequencies."
"This is a huge step - moving from microwave and radio frequency cloaks right up to the threshold of the visible," says Pendry."
Berkeley researchers claim that their cloak will work with light across wavelengths of 1,400-1,800 nanometres, while Lipson claims hers shall work at wavelengths as low as 1000 nanometres.However, visible light has wavelengths even lower, 400-700 nanometres.
"Because silicon absorbs visible light, a different material, such as titanium oxide would need to be used to create a carpet that could fool the human eye, Pendry notes. And then there would be the complications of fabricating a cloak in three dimensions."
"We can use this carpet to manipulate light on the nano-scale in silicon chips, avoiding obstructions that would normally scatter it," Zentgraf explains. Zhang also envisages the carpets being used to hide defects in the expensive, finely patterned lithography masks used to etch circuits into a silicon chip. But a cloak that would actually render objects invisible "is still a scientific fantasy at this point," he adds."
Fantasy indeed but somehow with the rapidly advancing technology at hand its safe to say we might have magic carpets that turn things invisible quite soon. What if they got into the wrong hands though?!
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