Carbon nanotubes used to demodulate AM radio signals

Posted by Rick C. Hodgin

Irvine (CA) - Electrical engineers at the University of California Irvine have developed a 1.5 volt biased carbon nanotube receiver which can convert AM radio waves into sound.  The system looks like a laboratory experiment right now, but demonstrates the EM signal detection capabilities of carbon nanotubes in a very straight-forward way.

Researchers began with the basic component of any modern music system, an iPod.  They then ran its output through a device which took the modulated audio signal and converted it to AM radio waves at 1 GHz.  The signal was broadcast through the air to a receiving device which contained a carbon nanotube detector, a 1.5 volt battery, an amplifier and speaker.  Overall, the signal demonstrated traveled just a few feet, but it was demonstrated that it could be blocked by placing an aluminum plate between the transmitter and the receiver.  In addition, when the 1.5 volt battery was remove the carbon nanotube was no longer biased and the sound quality dropped to almost static and white noise.  Inserting the battery brought back the sound.

The basic radio components are 1) Transmitter, 2) iPod, 3) transmit antenna, 4) receive antenna, 5) bias plus carbon nanotube modulator, 6) battery, 7) preamplifier and 8) speakers.

The carbon nanotubes were grown in the lab.  They then had palladium electrodes grafted onto them through optical lithography.  The device was constructed and tested using relatively straight-forward radio components.  The team performing the work consisted of only two researchers, associate professor Peter J. Burke and Chris Rutherglen.

The practical applications of a carbon nanotube based receiver are not found easily in AM radio transmissions, which rely on a constant frequency and variable signal amplitude for conveyance.  The true potential lies in more complex systems, such as tunable frequency applications.  Now that it's been shown that a carbon nanotube can attenuate radio waves accurately, the possibility exists of increasing the frequency and moving from AM signals to FM and PCM (Pulse Code Modulation).  These kinds of signals are used typically with wireless devices, including cell phones and WiFi.

Carbon nanotubes are proving to be very capable in a wide array of disciplines.  It would not surprise TG Daily to learn that this foundational component wiles its way into many devices of the future.  So far the carbon nanotubes have been shown to be excellent conductors of heat, both conductors and insulators of electricity with proper doping or other structures added, and now electrical modulation.