March/April 2008

TR10: NanoRadio

Alex Zettl's tiny radios, built from nanotubes, could improve everything from cell phones to medical diagnostics.

By Robert F. Service

Tiny tunes: A nanoradio is a carbon nanotube anchored to an electrode, with a second electrode just beyond its free end. Credit: John Hersey

Multimedia •  See and hear the nanotube radio.

Who: Alex Zettl, University of California, Berkeley Definition: At the core of the nanoradio is a single molecule that can receive radio signals. Impact: Tiny radio devices could improve cell phones and allow communication between tiny devices, such as environmental sensors. Context: New nanotech tools are allowing researchers to fabricate very small devices. The nanoradio is one of the latest.

If you own a sleek iPod Nano, you've got nothing on Alex Zettl. The physicist at the University of California, Berkeley, and his colleagues have come up with a nanoscale radio, in which the key circuitry consists of a single carbon nanotube.

Any wireless device, from cell phones to environmental sensors, could benefit from nanoradios. Smaller electronic component­s, such as tuners, would reduce power consumption and extend battery life. Nanoradios could also steer wireless communications into entirely new realms, including tiny devices that navigate the bloodstream to release drugs on command.

Miniaturizing radios has been a goal ever since RCA began marketing its pocket-sized transistor radios in 1955. More recently, electronics manufacturers have made microscale radios, creating new products such as radio frequency identification (RFID) tags. About five years ago, Zettl's group decided to try to make radios even smaller, working at the molecular scale as part of an effort to create cheap wireless environmental sensors.

Zettl's team set out to minia­turize individual components of a radio receiver, such as the antenna and the tuner, which selects one frequency to convert into a stream of electrical pulses that get sent to a speaker. But integrating separate nanoscale components proved difficult. About a year ago, however, Zettl and his students had a eureka moment. "We realized that, by golly, one nanotube can do it all," Zettl says. "Within a matter of days, we had a functioning radio." The first two transmissions it received were "Layla" by Derek and the Dominos and "Good Vibrations" by the Beach Boys.

The Beach Boys song was an apt choice. Zettl's nano receiver works by translating the electromagnetic oscillations of a radio wave into the mechanical vibrations of a nanotube, which are in turn converted into a stream of electrical pulses that reproduce the original radio signal. Zettl's team anchored a nanotube to a metal electrode, which is wired to a battery. Just beyond the nanotube's free end is a second metal electrode. When a voltage is applied between the electrodes, electrons flow from the battery through the first electrode and the nanotube and then jump from the nanotube's tip across the tiny gap to the second electrode. The nanotube--now negatively charged--is able to "feel" the oscillations of a passing radio wave, which (like all electro­magnetic waves) has both an electrical and a magnetic component.