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Metamaterials

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Original author: 
John Timmer

FirasMT

In the past few years, there have been a regular series of announcements about devices that cloak something in space. These typically bend light around the cloak so that it comes out behind the object looking as if it had never shifted at all. In contrast, there's just been a single description of a temporal cloaking device, something that hides an event in time. The device works because in some media different frequencies of light move at different speeds. With the right combination of frequency shifts, it's possible to create and then re-seal a break in a light beam.

But that particular cloak could only create breaks in the light beam that lasted picoseconds. Basically, you couldn't hide all that much using it. Now, researchers have taken the same general approach and used it to hide signals in a beam of light sent through an optical fiber. When the cloak is in operation, the signals largely disappear. In this case the cloak can hide nearly half of the total bandwidth of the light, resulting in a hidden transmission rate of 12.7 Gigabits per second.

The work started with the Talbot effect in mind, in which a diffraction grating causes repeated images of the grating to appear at set distances away from it. The cloaking device relies on the converse of this. At other distances, the light intensity drops to zero. The key trick is to convert the Talbot effect from something that happens in space to something that happens in time.

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Whether you live in a town, city, or countryside, noise is everywhere. Urban planners and civil engineers have been taking noise into account, and, modern apartments often have pretty good sound insulation. But, lets face it, in the middle of the night, noises do tend to creep through (and sometimes make you wish you were at the party in the neighboring apartment).

New materials that have the potential to create acoustically shielded environments may be on the way. In the latest development, researchers have shown how creating materials that have meandering paths for sound waves can result in a negative acoustic index of refraction. More importantly, these materials may actually be manufacturable and work for sound waves in air—the stuff we might consider noise.

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