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Zettl explains that the "nanotube does not act as an antenna in the conventional sense." That is, instead of picking up electromagnetic waves electrically, it picks them up mechanically. This happens because of the nanotube's natural resonance frequency. As soon as it encounters radio waves that match the frequency, the nanotube starts vibrating in step with the waves, effectively tuning in only to that radio signal. The nanotube's vibrations change the field emission current, and the mechanical vibrations are converted into an electrical signal. An external battery powers the field emission current and amplifies the radio signal. The field emission is naturally asymmetrical--it allows current to flow only in one direction, just like the diodes and rectifiers used in demodulators. So the nanotube also acts as a demodulator and detects the music encoded onto the carrier wave.
To tune to a different radio station, the researchers change the resonance frequency of the nanotube. They do this by changing the voltage applied across the electrodes. "It's like tuning a guitar string," Zettl says. "The electric field pulls on the nanotube." With the same nanotube, the researchers can cover the entire FM radio band.
Cees Dekker, a nanotube researcher at the Delft University of Technology, in the Netherlands, calls the new radio "an appealing demonstration that very simple devices can be used for everyday [tools]." Whether or not the device is used for sensors remains to be seen, he says, but for now, the simple demonstration is a good start.
Alex Zettl's tiny radios, built from nanotubes, could improve everything from cell phones to medical diagnostics.
Software can predict the best designs for fabricating logic gates from disorganized carbon nanotubes.
Excellent observation Killian. At the very real risk of confusing the whole matter, I would guess that the Chu-Harrington Limit would impose restrictions on the reduction of a standard dipole configuration. The problems surrounding the demodulation process could very well start with the inductance levels of mixed carbon nanotube bundles. Although there is definitely a high degree of sophistication involved with its construction, I am old enough to have listened to one of the earliest 'crytal' radio sets and marvelled at how well such a simple device managed to tune in the signal on a carrier wave.
Does the Chu-Harrington Limit apply to antennae working by physical resonance like the nanotube?
This receiver device may be electrostatically tunable over the 20 MHz FM band, (88MHz to 108MHz), but isn't it demonstrating amplitude modulation (AM) rather than frequency modulation (FM)?
First application that comes to mind: "Tricorder sensors"...
Missing some useful information here... What environment is required for this "performance"? Vacuum would be unfortunate but seems most likely -- I guess "open to the atmosphere" is unlikely.
I immediately see this as potentially a magnitudes-more-sensitive equivalent to some of the MEMS-based chemical sensors which are able to detect the presence of trace amounts of compounds (almost down to the "homeopathic" range ;) by detecting changes in resonant frequency of a vibrating mass resulting from binding some minimal number of molecules of the compound in question...
Conceivably could assay a whole library of molecules by creating a whole "forest" of these tubes, and defining particular "woodlots" as each getting capped with a different "sensor" molecule.
Nice how your description implies that sensor measurements can be accomplished en-masse, by monitoring variations in swept-frequency responses, where variations in field-emission currents could easily translate into useful two-dimensional metrics across a mapped landscape of "woodlots".
Re: First application that comes to mind: "Tricorder sensors"...
Have to read it twice, closer the second time.
"vacuum", of course.
Ah, well.
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74 Comments
how well do nano-antennas work?
Doesn't the Chu-Harrington Limit suggest a nano antenna would have very low bandwidth? If so, can this lead to practical devices, or is it just interesting? (I'm no expert in antennas, so this is a real question, not a comment.)
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