Tiniest Radio Consists of a Single Carbon Nanotube
Researchers have fabricated what they call a true "iPod Nano"--a fully functional radio made out of a single carbon nanotube (CNT). At 10,000 times thinner than a human hair, the researchers hope the radio could have applications for new wireless communications devices, as well as medical applications such as hearing aids.
The tiny radio can play songs and sounds broadcast by both AM and FM radio stations, in the commercial range of 40-400 MHz. The first song played by the CNT radio was Eric Clapton's "Layla," which can be heard here . It's a little fuzzy, but no worse than a car radio when you're driving through a tunnel.
The researchers, from the Lawrence Berkley National Laboratory, have surpassed the second smallest radio by several orders of magnitude. Leading inventor Alex Zettl explains that the nanotube simultaneously serves as all parts of the radio, including the antenna, tunable band-pass filter, amplifier, and demodulator.
The radio basically consists of a CNT mounted on an electrode, close to a counter-electrode, all contained in a vacuum similar to the configuration of a vacuum tube. A battery or other source of DC voltage provides power to the electrode.
The researchers explained that the nano radio is not a miniature version of an electronic radio, but works completely differently. The radio is based primarily on electro-mechanical movement, like a true NEMS (NanoElectroMechanical System) device.
The nanotube has an electrically charged tip, and can be tuned to a desired frequency after fabrication by the applied DC bias. When the frequency of the incoming radio waves matches this resonant frequency of the nanotube, the nanotube vibrates. Then the electrically charged tip turns these mechanical vibrations into sound. With help from the battery, the radio signal is amplified.
Because nanotubes are too small to be seen even under the highest powered optical microscope, the scientists viewed the radio using a transmission electron microscope, where an electron beam (which has a shorter wavelength than a photon beam) is transmitted through the nanotube.
Since the nanotube radio basically assembles itself, the researchers hope that it will be relatively easy to mass produce. They plan on fabricating tiny radio receivers, wireless communication devices and monitors, and medical devices such as tiny hearing aids.