Ideas

Brainiac

How to be invisible

Until now, only magicians and superheroes could fulfill our fantasies of being able to make things vanish. But a recent study reveals that it is possible to build an invisibility cloak made from everyday materials.

The idea, cooked up by the Toyota Research Institute of North America, works with the basic principles of light.

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We see objects when light bounces off of them and into our eyes. For example, we can make out the shape of a bookshelf in the dark when beams from a nightlight reflect off the shelf’s edges and then scatter into every direction, including the direction of our eyes.

But to make a bookshelf disappear, scientists knew that they would need to reroute the light around it, thereby creating a visual black hole where the object stood. That was previously thought impossible to achieve with everyday materials. Only highly engineered substances, known as metamaterials, coupled with the perfect storm of environmental circumstances, could get light to do a trick like that. Or so people thought.

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“[Past] work has not been practical for real application because it requires very complicated material design and it requires extreme barometers,” said Debasish Banerjee, senior manager of the Toyota Research Institute of North America and part of the study. “So, when we started to work on this, we thought, ‘How are we going to make this technology practical so that we can use it?’ ”

Banerjee and his colleagues decided to approach the problem with mirrors and polarizers — easy-to-find optical filters that prevent certain types of light waves from coming through — in an attempt to obscure how an object is seen.

To do this, they built a “cloak” that would, in effect, project whatever was behind the “invisible object” in front of it, creating a simple optic fake-out. Their cloaking device was a mirrored box surrounded by polarizing lenses. Objects that the researchers wanted to “disappear” — in this case, a yellow cylinder — were inserted in the box. They then put a toy car behind the box. The light hitting the car bounced off the mirrors and through lenses, essentially bending around the cylinder. The light was then refocused as a projection of the car in front. While the cylinder appears to have vanished, it’s merely been replaced by an image of what was behind it.

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“This would be the first time they’re combining an invisibility cloak with the projection of an image,” said Xiang Zhang, a University of California Berkeley engineering professor who was an author of the first-ever optical cloak study in 2009. “That’s really cool — we never thought about doing those things together.”

Zhang imagined a scenario where he could someday wear the “cloak” box over his head to hide his face but then project a dinosaur’s head instead.

“Basically, you create a hybrid image,” he said.

The study hasn’t been applied to product design yet, but scientists do have ideas about how this technology could be used. Car makers might improve safety by cloaking blind spots to give drivers a completely unobstructed view, or by projecting a meter onto the dashboard that shows how quickly nearby vehicles are approaching. Cellphones or hand-held video games may also use this trick to become transparent, revealing only the display on their screens.

But for now, the rest of us can relax knowing that we have the power to make things vanish, kind of.

Kelly Kasulis is a journalist living in Boston and the deputy digital editor of The GroundTruth Project. Follow her on Twitter @KasulisK.
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