The World’s Smallest Radio
A single carbon nanotube can function as a radio that detects and plays songs. The nanotube radio was invented in 2007 by physicist Alex Zettl and his colleagues at the University of California, Berkeley. Their invention performs a set of amazing feats: a single carbon nanotube tunes in a broadcast signal, amplifies it, converts it to an audio signal and then sends it to an external speaker in a form that the human ear can readily recognize. The nanotube radio could be the basis for a range of revolutionary applications: hearing aids, cell phones and iPods small enough to fit completely within the ear canal. The nanoradio “would easily fit inside a living cell,” Zettl says. “One can envision interfaces to brain or muscle functions or radio-controlled devices moving through the bloodstream.”
Zettl, who directs 30 investigators engaged in creating molecular-scale devices, decided to make nanotubes a focus of his work because they are remarkable structures. The question of who first discovered them is controversial, but Japanese physicist Sumio Iijima is generally credited with having put them on the scientific map, when in 1991 he announced finding “needlelike tubes” of carbon on the tip of a graphite electrode that emitted an arc, a luminous discharge of electricity.
Today, the word “nano” applies to anything small, even down to the “nanoparticles” in commodities as diverse as motor oil, sunscreen, lipstick and ski wax. Zettl got the idea for a nanoradio when he decided he wanted to create tiny sensing devices that could communicate with one another and broadcast their observations wirelessly. “They were to do monitoring of environmental conditions,” he says. They would be distributed in the field near some factory or refinery and would radio their results back to some collecting point. Anyone could then go to Google “and click on the air quality of a city and see it in real time.” During the course of some experiments aimed at producing a nanotube mass sensor, one of Zettl’s graduate students, Kenneth Jensen, found that if one end of a carbon nanotube was planted on a surface, creating a cantilever, the beam would vibrate when a molecule landed on its free end. Molecules of different masses would make the beam vibrate at different frequencies. When Zettl noticed that some of these frequencies included those in the commercial radio band, the idea of using the cantilevered nanotube to make a radio became virtually irresistible.
In January 2007 Zettl, Jensen and two other Berkeley researchers, Jeff Weldon and Henry Garcia, performed an experiment and mounted a multiwalled carbon nanotube on a silicon electrode and placed a counterelectrode about a micron away, connecting the two by wire. They also attached a DC battery to the apparatus to set up a small field-emission current between the nano¬tube tip and the counterelectrode. To actually see what would happen during the course of a radio transmission from a nearby antenna, they placed their device inside a high-resolution transmission electron microscope (TEM). Then they started broadcasting.
The experimenters documented the entire process -audio and video- and converted the recording to a QuickTime movie that they posted on the Zettl Group’s Web page, where anyone can download and play it for free. Later, they used “Good Vibrations,” by the Beach Boys; the “Main Title” theme from Star Wars, by John Williams; and the largo from Xerxes, the opera by George Frideric Handel. “This is the first song ever transmitted using radio,” Zettl explains.
Zettl and his colleagues withheld news of the nanoradio for several months, until it could be published in Nano Letters, a journal of the American Chemical Society. The apparatus had its formal debut online in October 2007 and then in the November print edition.
Source: sciam.com.