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26 March 2010 ARS Technica

Old-school TV aerials inspire new nanoscale optical antennas

Once arranged, the nano-antenna array was able to direct visible light on the scale of its tiny antenna bars
Once arranged, the nano-antenna array was able to direct visible light on the scale of its tiny antenna bars.
Image Credit: NASA.

A paper published in Nature this week details how researchers have taken a common antenna design and replicated it on the the nanoscale level. When a regular TV aerial that handles radio frequencies is scaled down to nanometer sizes and slightly modified, the result was a tiny antenna that could direct light of nanometer wavelengths. The resulting optical antenna array could help improve the design of nanoscale sensors and detectors.

Those old TV antennas, consisting of multiple crossbars, are called Yagi-Uda antennas, named for their inventors. The design of Yagi-Uda antennas is based on a simple principle: a metallic wire resonates strongly if its length matches half of the relevant wavelength. To tune into TV and radio wavelengths, which are around a meter long, the Yagi-Uda uses bars of half that length to pick up the appropriate signals. The design proved to be popular because it is highly directional and can receive or broadcast a strong signal.

To make the design work at the nanoscale level, scientists made tiny crossbars, about a hundred nanometers long, and arranged them in the Yagi-Uda configuration. They made a slight alteration in the design so that the feed bar was tilted 45 degrees, allowing it to be excited by an electric field in a manner that is independent of the other bars.

Once arranged, the nano-antenna array was able to direct visible light on the scale of its tiny antenna bars. The resonant wavelengths were around a few hundred nanometers, corresponding to the orange and red sections of the spectrum—that's a larger multiple of the antenna bar length than the standard Yagi-Uda antenna, but still quite useful. The nano-array's creators hope that the itty-bitty antenna will find wide use in optical nanotechnology.

Source: ARS Technica /...

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