Tuesday, May 22, 2012

Scientists create invisible 'spying' device

Invisibility devices are no longer something that is only found in science fiction. Scientists have come up with clever ways to 'hide' objects from reality, and a recent attempt by Stanford University yielded a device that can see without being seen. Their spying device was developed by clever use of materials that cancel out the light that would normally reveal its presence.

For their device, the Stanford researchers utilized a field of physics known as plasmonics. It describes oscillations of electrons resulting from light hitting metal. Oscillations create tiny currents and light emission, and the scattering of light can be used to hide objects from reality: when two waves meet, they can either reinforce each other, or cancel each other out. The latter is called destructive interference, and is necessary to stop things from being seen. As we rely on light waves hitting our eyes for our vision, something that does not emit or scatter light cannot be seen.

The Stanford scientists created a device that consists of a mixture of silicon and gold. Silicon is known to absorb light and it can produce an electrical current, making it suitable for use as a light detector. But it also scatters and reflects incoming light waves, which means it can be picked up by our eyes. By carefully 'tuning' the plasmonic properties of the gold, that was used as coating for the device, the scientists created light waves that cancel out those coming from the silicon.

Adding silicon and fine tuned gold results in destructive interference, meaning the light waves coming from the device have been cancelled out. That means, we cannot see it, as has been proven by the scientists, even though gold is naturally quite reflective and visible to our eyes. Calculations revealed that light emission of the device after tuning the gold was reduced by a 100-fold, while light absorption, necessary for the detector to function, dropped only 4-fold.
Gold colour shows 'bare' silicon, while the black parts are covered with a fine tuned gold coating.
An invisible light detector can be used for a variety of devices, such as imaging. Cloaked pixels in a camera could help make images sharper, but the optic properties of the invisibility device can also make solar panels and lasers more effective. Even though the scientists do not mention it, a device that can see but not be seen could also be used for other, more secretive endeavours. However, creating an actual spying device such as a completely invisible camera is probably not yet possible using this technique. Whatever it is used for, making something invisible by giving it a gold coating is pretty amazing by itself.

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