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Video file: Microwave refracting composites allow invisibility cloaks to be built on 3D printer

Duke University Pratt School Of Engineering : 28 May, 2013  (Special Report)
A team led by scientists at Duke University's Pratt School of Engineering has demonstrated the first working "invisibility cloak." The cloak deflects microwave beams so they flow around a "hidden" object inside with little distortion, making it appear almost as if nothing were there at all.

It may not be quite as versatile as Harry Potter's famous invisibility cloak just yet, but researchers have unveiled the first cloaking device anyone with a 3D printer can create themselves.

A metamaterial - a type of man-made composite - uses microscopic modulations in its surface to refract microwaves (and one day waves from visible light?) around an object. Current incarnations of the cloak have been made from fibreglass and copper, but Urzhumov and his team decided to experiment with a 3D-printed polymer-based cloak.

Three-dimensional printing, or stereolithographic fabrication,
has become increasingly popular, not only among industry,
but for personal use. It involves a moving nozzle guided by a
computer program laying down successive thin layers of a
material - usually a plastic - until a three-dimensional object
is produced. Researchers have created everything from a
working gun to replacement car parts using 3D printers.



 The design resembles a Frisbee made of Swiss cheese. However, each hole help to deflect microwave beams, making devices at its centre appear invisible to microwave beams.

The 3D printer "eliminates the 'shadow" that would be cast and makes it easier for something to be invisible. A bright, highly reflective object, like a metal cylinder, is made invisible. The microwaves are carefully guided by a thin dielectric shell and then re-radiated back into free space on the shadow side of the cloak.

The disk-like cloak has an open area in its centre where the researchers placed an opaque object.
Algorithms determined the location, size and shape of the holes to deflect microwave beams, and the fabrication process takes from three to seven hours.

When microwave beams were aimed at the object through the side of the disk, the cloak made it appear that the object was not there.


Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering, believes the technique will be appropriate for building cloaks that are several metres in diameter, but still fairly thin at 2.5cm. Current cloaks are more suited to shielding aircraft from radar, but 3D printing enthusiasts will be holding their breath for the moment the visibile light cloak CAD instructions go live.

A 3D printer called a MakerBot from the US costs around £600 and uses reels of plastic to print objects.

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