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A flawless invisibility cloak: Finally a reality?

Duke University researchers perfect the illusion of invisibility using a new light-bending method

Over the past few years, the science world has produced no shortage of invisibility cloaks. But unlike the magical, fictional kind donned by Harry Potter and Co., these shimmery offerings were less than perfect: While most could bend light around an object, they all reflected some of what's called incident light, compromising the illusion's success. Now for the first time, researchers from Duke University have created a "flawless" invisibility cloak capable of disguising tiny objects, in this case a 7.5 by 1 cm cylinder.

Invisibility cloaks typically work by bending electromagnetic waves — like visible light — around a three-dimensional object. Rather than seeing that object, onlookers instead catch a glimpse of what's directly behind it. Scientists are able achieve this illusion using something called metamaterials, or man-made objects that never occur in nature but can bend electromagnetic waves in all sorts of weird ways.  

However, the degree to which these metamaterials can bend something like light is limited. Sebastian Anthony at ExtremeTech explains:

[M]etamaterials get you most of the way, but they still need to be arranged in such a way that the illusion is perfect. To get around a 3D object, you have to turn a corner at some point — and previous cloaks have struggled to fashion metamaterials that bend waves around corners without causing reflections, which ruin the illusion.

In this case, Duke University researchers came up with a so-called "perfect arrangement": Position the metamaterials in a diamond pattern that eliminates reflective light entirely. In this experiment, they were able to hide the miniature cylinder completely from a different kind of electromagnetic wave, but one whose properties still translate, at least in theory, to visible light — microwaves. 

The diamond arrangement has its limitations, however: It only works in one direction. "It's like the card people in Alice in Wonderland," Prof. David Smith, a Duke researcher who worked on the project, tells BBC News. "If they turn on their sides you can't see them but they're obviously visible if you look from the other direction." 

But the design principle is a big step forward in the quest to prove that total invisibility is indeed possible. In the near future researchers hope to apply their findings to an omnidirectional cloak that can hide an object no matter where an observer is situated.

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