Complete radio built with a single carbon nanotube

Complete radio built with a single carbon nanotube

The one ten-thousandth the diameter of a human hair radio needs only a battery and earphones

Physicists at the University of California, Berkeley, have built the smallest radio yet a single carbon nanotube one ten-thousandth the diameter of a human hair that requires only a battery and earphones to tune in to your favorite station. The nanoradio receiver could be used in any number of applications from cell phones to microscopic devices that sense the environment and relay information via radio.

Alex Zettl, UC Berkeley professor of physics, graduate student Kenneth Jensen, and their colleagues in UC Berkeley’s Center of Integrated Nanomechanical Systems (COINS) worked with the Materials Sciences Division at Lawrence Berkeley National Laboratory on research supported by the National Science Foundation.

Nanotubes exhibit unusual electronic properties because of their size, which, for the nanotubes used in the radio receiver, are about 10 nm in diameter and several hundred nanometers long. In the radio, a single carbon nanotube works as an all-in-one antenna, tuner, amplifier and demodulator for both AM and FM. The nanoradio detects signals in a radically new way it vibrates in tune with the radio wave. It is a true nanoelectromechanical device that integrates the mechanical and electrical properties of nanoscale materials.

Nanoradio detects signals by vibrating in tune with the radio wave.

The nanotube is placed in a vacuum and hooked to a battery, which covers its tip with negatively charged electrons, and the electric field of the radio wave pushes and pulls the tip at the RF frequency.

Although it might seem that the vibrating nanotube yields a “one station” radio, the tension on the nanotube also influences its natural vibration frequency and the physicists tune in a desired frequency or station by “pulling” on the free tip with a positively charged electrode. This electrode also turns the nanotube into an amplifier. The voltage is high enough to pull electrons off the tip of the nanotube and, because the nanotube is simultaneously vibrating, the electron current from the tip is an amplified version of the incoming radio signal. This is similar to the field-emission amplification of old vacuum tube amplifiers used in early radios and televisions. Finally, the field-emission and vibration together also demodulate the signal. The amplified output of this simple nanotube device is enough to drive a very sensitive earphone. For more information, visit http://www.berkeley.edu/news/media/releases/2007/10/31_NanoRadio.shtml.

Jim Harrison