Nanotube Made into World's Smallest Radio

Mason Inman
for National Geographic News

November 5, 2007

Apple's iPod Nano may be small, but now researchers have made a radio that really deserves the title "nano."

A carbon nanotube—a hollow, tube-shaped molecule 10,000 times smaller than a human hair—can perform all the basic functions of a radio when it's wired up to a few other simple parts, a new study shows.

The simple tube is ten carbon atoms wide and only a few hundred nanometers long.

Alex Zettl and colleagues at the University of California at Berkeley showed that a nanotube can work as an antenna, picking up radio signals from the air.

In the experiment, a nanotube was attached to a copper wire and encased inside a tiny vacuum chamber.

The researchers found the same nanotube can also work as a tuner and pick up a specific channel AM and FM channel. It can also amplify the signals.

Finally, the tube can turn information from the signal into an electric current—like the current that flows through the power cord to your computer—so that sound could be played through speakers or headphones.

"The real breakthrough is to have one nanotube do all these things," Zettl said.

The new findings were published last week in the journal Nano Letters.

Tuning In

Various research groups have made nanotubes that could perform one or another of these functions, Zettl said.

"But we weren't sure how to integrate it all together," he said.

A key step was the discovery that nanotubes vibrate when they pick up a radio signal.

The scientists could then dial in precise stations by running electricity through a copper wire near the nanotube, making it more or less difficult for the nanotube to wiggle.

"It's like a guitar string," Zettl said. When you pluck the string, it vibrates with certain note, and if you tighten or loosen the string, it makes the note rise or fall.

To do more rough tuning—say, to change a nanotube that picks up AM stations into one that catches FM signals—the researchers had to shorten the nanotubes.

They did this by running a lot of electricity through the tubes, which made carbons atoms shoot off the tip.

The shorter nanotubes then resonated at a higher frequency, picking up a different range of radio signals.

"We can cover the full range [of FM or AM], but not with one nanotube," Zettl said.

The researchers received their first FM broadcast last year: Derek & The Dominos' "Layla" and the Beach Boys' "Good Vibrations" were transmitted from across the room.

(See a photo of a high-powered microscope for spotting nanoparticles.)

Nanotube Innovation

"This breakthrough is a perfect example of how the unique behavior of matter in the nanoworld enables startling new technologies," said Bruce Kramer, a senior advisor for engineering at the National Science Foundation, which funded the work.

Other research groups are also been hot on the trail of a nanotube radio.

In work to be published soon, John Rogers and colleagues at the University of Illinois at Urbana-Champaign, have made an array of six carbon nanotubes that together perform all the functions of a radio.

Whereas Zettl's nanotube radio needs some additional amplifying to produce a signal that could feed into headphones, Rogers said that with his setup, "the headphones literally plug into a nanotube device."

The nanotube radios could also work with tiny sensors in the environment that monitor air and water quality, Zettl said. (Related news: "'Smart Dust' Sensors to Be Used for Eco Detection" [November 14, 2006].)

"Having sensors collecting and relaying information is power intensive," Zettl said. But with the nanotube radio, they could drastically cut the amount of power needed.

For these applications, the nanotubes would not only have to pick up radio signals, but also broadcast them.

This works on the same physical principles, Zettl said, so the researchers "could reconfigure our radio to broadcast."

For most of these applications, nanotube radios also need a power source, such as a tiny battery, he added.

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