10 November 2007

The old is new again: a nanotube crystal radio

Nanowerk has an especially nice description of a nifty development at my alma mater, U.C. Irvine:
Researchers in California have now reported another step towards showing nanoelectronics in systems: They have developed the world's first working radio system that receives radio waves wirelessly and converts them to sound signals through a nano-sized detector made of CNTs...

Peter Burke and Chris Rutherglen at the University of California, Irvine developed a CNT demodulator (a device that converts the radio frequency signal from the carrier into baseband signals such as video, audio, or data for further processing or amplification) that is capable of translating AM (amplitude modulation) radio waves into sound. In a laboratory demonstration, the researchers incorporated the detector into a complete radio system and used it to successfully transmit classical music wirelessly from an iPod to a speaker several feet away from the music player. In this setup, the carbon nanotube functions in the critical role as the receiver's AM demodulator. Burke, an Associate Professor in Electrical Engineering and Computer Science and leader of the UCI Nanotechnology Group, and Ruthergle, a grad student in Burke's group, reported their findings in the October 17, 2007 web edition of Nano Letters ("Carbon Nanotube Radio").

"Our CNT-based amplitude-modulated demodulator is effective at detecting the modulation signal up to 100 kHz" Burke tells Nanowerk. "We also successfully demonstrated our demodulator in an actual AM radio receiver operating at a carrier frequency of 1 GHz and capable of demodulating high-fidelity audio."

...Digging into their publication in the American Chemical Society's Nano Letters, Rutherglen and Burke describe how their clever application of a carbon nanotube performs the exact same function the shiny gray/silver lead sulfide crystal did in the crystal radio sets of our childhood (at least, those of us Of A Certain Age): they're leveraging the device's nonlinear voltage-to-current behavior to detect the amplitude modulation of a carrier wave, in this case a 1GHz carrier.

Now, a post-publication appendix to the ACS report by Rutherglen and Burke notes that some similar work has been done independently in as-yet-unpublished work by the group of Professor John Rogers at the University of Illinois at Urbana-Champaign, and Doug Natelson (whose informative Nanoscale Views blog I've added to my list of links) notes that the UCI development is perhaps receiving more than its fair share of attention given that something roughly similar has been done on an even finer scale using an AFM a couple years ago, but nevertheless I tip my hat to the UCI team: this is taxpayer-supported research, and folks who might not read professional ACS publications deserve to know what their withheld wages have accomplished. Besides, nanotech is exciting, and I love the parallels with crude crystal radios and what that says about the future of this sort of thing. Nice job, folks.