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Five Ways Science Can Make Something Invisible

Stealth tanks, invisibility cloaks, mirages and other invisible innovations could be closer than you'd think

This stealth tank can change its surface temperature at will, making it invisible to infrared cameras. Image courtesy of BAE.

In our latest issue, we considered the concept of invisibility in all types of forms—an artist who camouflages himself as a political statement, the invisible malaria parasite, and people who see encrypted codes hiding vital information everywhere they look. Now we turn to the many ways in which scientists and engineers are literally cloaking objects, sounds and even moments using cutting-edge technology. These cloaking devices don’t just trick our eyes; they deceive mechanical sensors that detect different forms of energy, from light waves to magnetic radiation.

1. Some Like it Cool

It’s not easy to hide a tank, even at night. An infrared camera readily detects heat from the engine exhaust or rising off the armor after being in the sun all day. But British defense company BAE has developed a system that uses thousands of hexagonal metal panels, each a few inches in diameter, to cover a vehicle and render it invisible to infrared sensors (see above). On-board thermal cameras detect the background temperature, and the panels—which can be rapidly heated or cooled—are programmed to continually mimic it. The panels can even be set to resemble a more innocuous vehicle, like a car. They may be ready for commercial production as early as 2013.

2. Personal Magnetism

This past March, engineers in Spain and Slovakia took commercially available materials and made something rather extraordinary. Put a metal object in their small cylindrical container and it won’t be detected by airport security systems or MRI machines. The canister is made up of two concentric layers—an inner superconducting material that repels magnetic fields, and an outer material that attracts them. When combined, they make the invention (and its contents) invisible to metal detectors and other machines that rely on magnetism. The device may someday be useful to medical patients with pacemakers, allowing them to undergo exams by MRI machines without distorting the image.

The “magnetic invisibility coat” combines an inner coating that repels a magnet’s field with an outer layer that attracts it. Image via J. Pact-Camos, C. Navau & A. Sanchez

3. A Vow of Silence

Next time you’re annoyed by a crying baby or a blaring TV, pin your hopes on a new device developed at Germany’s Karlsruhe Institute of Technology. It’s the aural equivalent of an invisibility cloak: sound waves are unable to enter or exit the outside of the high-tech disc. The plate is made up of micro-structured materials that speed incoming sound waves around the perimeter, so to a listener, they arrive at the other side as though they simply passed straight through it without interacting with anything inside. Someday, the principles used in the proof-of-concept device could be used to silence a particular source of sound pollution—or create a small refuge of quiet in a noisy world.

4. Manufacturing a Mirage

You’re riding down a sun-baked highway and in the distance appears a shimmering pool—a mirage. Researchers at the University of Texas at Dallas have harnessed this effect to make objects seemingly vanish underwater. Mirages occur when a large change in temperature over a small distance bends light rays that are headed for the ground, making them instead head horizontally toward your eyes. (Thus, a patch of blue sky is deflected so that it appears directly ahead of you, resembling a pool of water.) The scientists created their mirage by heating a one-molecule-thick transparent curtain—made from of carbon nanotubes—to roughly 4,000 degrees Fahrenheit in a pool of water. An object hidden behind the curtain appears to observers as simply more water. The concept could theoretically be used to cloak submarines, or even lead to similar devices that work above water.

5. A Wrinkle in Time

When we “see” the world around us, we’re actually seeing light reflect off objects. And, since that light travels toward our eyes at nearly 186,000 miles per second, we perceive events as occurring instantaneously. But how would we perceive events if we could alter the speed of light? A team of researchers at Cornell University has effectively done just that. Earlier this year they published the results of an experiment that uses a “split time” lens. When light passes through the lens, the low-frequency wavelengths at the “red” end of the spectrum slow down, while the high-frequency wavelengths at the “blue” end of the spectrum speed up. This creates a brief gap or “temporal hole.” Next, the wavelengths of light are stitched back together, so that, to an observer, the beam appears to be continuous—and any event that occurred during the brief gap, just 40 trillionths of a second long, was effectively invisible. The researchers say practical applications include the ability to insert data into continuous fiber-optic data streams without causing interruptions.

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