World's first: Fully functional nanotube radio

of the radio signal is possible. Furthermore, since field emission is a non-linear process, it also acts to demodulate an AM or FM radio signal, just like the diode used in traditional radios.

“What we see then is that all four essential components of a radio receiver are compactly and efficiently implemented within the vibrating and field-emitting carbon nanotube,” said Zettl. “This is a totally different approach to making a radio — the exploitation of electro-mechanical movement for multiple functions. In other words, our nanotube radio is a true NEMS (nano-electro-mechanical system) device.” Because carbon nanotubes are so much smaller than the wavelengths of visible light, they cannot be viewed with even the highest powered optical microscope. Therefore, to observe the critical mechanical motionof their nanotube radio, Zettl and his research team mounted their nanotube radio inside a high resolution transmission electron microscope (TEM). A sine-wave carrier radio signal was launched from a nearby transmitting antenna and when the frequencies of the transmitted carrier wave matched the nanotube resonance frequency, radio reception became possible. “To correlate the mechanical motions of the nanotube to an actual radio receiver operation, we launched an FM radio transmission of the song Good Vibrations by the Beach Boys,” said Zettl. “After being received, filtered, amplified, and demodulated all by the nanotube radio, the emerging signal was further amplified by a current preamplifier, sent to an audio loudspeaker and recorded. The nanotube radio faithfully reproduced the audio signal, and the song was easily recognizable by ear.”

When the researchers deliberately detuned the nanotube radio from the carrier frequency, mechanical vibrations faded and radio reception was lost. A “lock” on a given radio transmission channel could be maintained for many minutes at a time, and it was not necessary to operate the nanotube radio inside a TEM. Using a slightly different configuration, the researchers successfully transmitted and received signals across a distance of several meters. “The integration of all the electronic components of a radio happened naturally in the nanotube itself,” said Jensen. “Within a few hours of figuring out that our force sensor was in fact a radio, we were playing music!”

The nanotube radio research was supported by the U.S. Department of Energy and by the National Science Foundation within the Center of Integrated Nanomechanical Systems.

-read more in K. Jensen, J. Weldon, H. Garcia, and A. Zettl. “Nanotube Radio,” Nano Letters (2 October 2007); and see supplemental materials at this Berkeley-Physics Web site. Note that the November 2007 print edition of Nano Letters will carry the paper by Jensen, Weldon, Garcia, and Zettl, and also a paper by Peter Burke and Chris Rutherglen of U.C. Irvine, reporting on the use of a carbon nanotube as a demodulator.

In the picture: Alex Zettl (left) and graduate student Kenneth Jensen / Source: Berkeley Lab