Boffins build radio from carbon nanotube

Physicists at the University of California, Berkeley have built the world's smallest radio from a single carbon nanotube.

The structure, which is one ten-thousandth the diameter of a human hair, needs only a battery and earphones to tune in to a radio station.

The scientists have already successfully received their first FM broadcast, Derek & The Dominos' Layla and The Beach Boys' Good Vibrations transmitted from across the room.

"We were just in ecstasy when this worked," said team leader Alex Zettl, UC Berkeley professor of physics. "It was fantastic."

The nano-radio, which is currently configured as a receiver but could also work as a transmitter, is 100 billion times smaller than the first commercial radios.

According to the researchers, it could be used in any number of applications from mobile phones to microscopic devices that sense the environment and relay information via radio signals.

The device would also integrate well with microelectronic circuits as it is extremely energy efficient.

"The nanotube radio may lead to radical new applications, such as radio-controlled devices small enough to exist in the human bloodstream," the authors wrote in a paper published online today in Nano Letters.

A single carbon nanotube in the nano-radio works as an all-in-one antenna, tuner, amplifier and demodulator for AM and FM.

It detects signals in a radically new way, however, vibrating thousands to millions of times per second in tune with the radio wave.

This makes it a true nanoelectromechanical device that integrates the mechanical and electrical properties of nanoscale materials.

In the nano-radio, the nanotube acts as the antenna to detect radio waves mechanically by vibrating at radio frequencies.

A single nanotube naturally selects only one frequency, the researchers explained. Although it might seem that the vibrating nanotube yields a 'one station' radio, the tension on the nanotube also influences its natural vibration frequency.

As a result, the physicists can tune to a desired frequency or station by 'pulling' on the free tip of the nanotube with a positively charged electrode.