The Hindu News Update Service
News Update Service
Friday, November 2, 2007 : 1625 Hrs
Sci. & Tech.
Single carbon nanotube is fully functional radio, receiving music over standard
radio bandwidth
Harnessing the electrical and mechanical properties of the carbon nanotube, a
team of researchers has crafted a working radio from a single fiber of that
material, according to Eurekalert, the news service of the American Association
for the Advancement of Science.
Fixed between two electrodes, the vibrating tube successfully performed the
four critical roles of a radio--antenna, tunable filter, amplifier and
demodulator--to
tune in a radio signal generated in the room and play it back through an
attached speaker.
Functional across a bandwidth widely used for commercial radio, the tiny device
could have applications far beyond novelty, from radio-controlled devices
that could flow in the human bloodstream to highly efficient, miniscule, cell
phone devices.
Developed at the National Science Foundation's (NSF) Center of Integrated
Nanomechanical Systems, a research team led by Alex Zettl of the University of
California at Berkeley announced the findings online on Oct. 31, 2007
(http://pubs.acs.org/journals/nalefd/index.html). The findings are scheduled to
be
printed in Nano Letters in November.
"This breakthrough is a perfect example of how the unique behavior of matter in
the nanoworld enables startling new technologies," says Bruce Kramer, a
senior advisor for engineering at NSF and the officer overseeing the center's
work. "The key functions of a radio, the quintessential device that heralded
the electronic age, have now been radically miniaturized using the mechanical
vibration of a single carbon nanotube."
The source content for the first laboratory test of the radio was "Layla," by
Derek and the Dominos, followed soon after by "Good Vibrations" by the Beach
Boys.
One of the primary goals for the center is to develop minuscule sensors that
can communicate wirelessly, says Settle. "A key issue is how to integrate
individual
molecular-scale components together into a system that maintains the nanometer
scale. The nanoradio achieves this by having one molecular structure, the
nanotube, simultaneously perform all critical functions," he adds.
The new device works in a manner more similar to the vacuum tubes from the
1930s than the transistors found in modern radios. In the new radio, a single
carbon fiber a few hundred nanometers (billionths of a meter) long, and only a
few molecules thick, stands glued to a negatively charged base of tungsten
that acts as a cathode. Roughly one millionth of a meter directly across from
the base lies a positively charged piece of copper that acts as an anode.
Power in the form of streaming electrons travels from an attached battery
through the cathode, into the nanotube, and across a vacuum to the anode via a
field-emission tunneling process.
"The field emission process could be likened to a runner jumping across a
ditch; you only make it across if you have enough speed, i.e. energy, to begin
with," says Zettl. "So electrons jump the physical gap from cathode to anode
when you supply enough energy to the device from the battery."
The stream of electrons along the nanotube changes when a radio wave encoded
with information--simply a wave of photons that travels in a controlled
manner--washes
across the tube and causes it to resonate. This mechanical action is what
amplifies and demodulates, or decodes, the radio signal.
Returning to Zettl's runner analogy, the vibrating nanotube is akin to a ditch
with a constantly changing width. Just as the runner's chances of making
the leap depend on how far the gap is, the chances of electrons making the leap
depend on the distance of the nanotube tip from the anode.
"This coupling of the mechanical waving motion of the nanotube to the success
rate of electrons jumping the gap is key to the functioning of the radio,"
says Zettl. "What emerges from the anode is then the information signal, which
can be transferred to additional amplifiers and a speaker to reveal the
originally encoded music or any other data."
By permanently lengthening or shortening the nanotube, a modification resulting
from sending a short-lived larger-than-normal electrical current through
the device, the researchers were able to control the frequency of the radio
signal that the device could receive.
The researchers believe it would be easy to produce such nanotube radios for
receiving signals in the 40-400 megahertz range, a range within which most
FM radio broadcasts fall.
The researchers fine tune the nanoradio to a frequency, akin to a channel, by
using the electrostatic field between the cathode and anode to tighten or
loosen the nanotube, a process the researchers relate to the tightening or
loosening of a string on a guitar. According to Zettl, the sensitivity of the
nanotube radio can be enhanced by attaching an external antenna or by using an
array of nanotubes that maintain the extremely small size.
While the concept of a miniaturized receiver for picking up broadcast music
signals has appeal, the technology has the potential to assist in a range of
interesting uses.
Adds Bruce Kramer, "The application of a fully functioning radio receiver less
than 50 millionths of an inch in length and one millionth of an inch in diameter
potentially allows the radio control of almost anything, from a single receiver
in a living cell to a vast array embedded in
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