Here’s a simple device. Stretch a sheet of graphene between two electrodes to form a kind of trampoline and then place a third electrode under the trampoline. Finally, send a DC current through the graphene and then add a radio frequency voltage on top to see what happens.
This is exactly the experiment that Yuehang Xu at Columbia University in New York and pals have done. They say the graphene sheet resonates when blasted with a voltage changing at radio frequency signals and that this can be easily measured by monitoring the capacitance between the sheet and the third electrode below the sheet.
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That’s a significant result. For some time now, physicists have been hoping to find ways of using nanoelectromechanical resonators to filter and generate radio signals directly. At present, this has to be done with various kinds of mixing techniques. The problem is that nanoelectromechanical devices all suffer from parasitic capacitance, which tends to drown out the signals that physicists are interested in at radio frequencies.
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Xu and co say their graphene sheet device is immune from this because its design causes the effects of stray capacitance essentially to cancel out. And they prove it by using their device to pick out a radio frequency signal at 33.27 MHz.
The device has the potential to do much better, they say. Graphene sheets are two orders of magnitude less massive than similar devices made of silicon and so can measure signals at much higher frequency. Xu and co say that with smaller sheets, they should be able to measure signals in the GHz range.
That’s the kind of speed that will interest the makers of mobile phones and other radio frequency communicators.
Of course, various problems will have to be ironed out before then. Not least of which is how to make graphene trampolines to order. Xu and co got their’s with tweezers. That won’t do for any kind of mass production.
Then there is the cooling problem. The new device works at 77K so its operating temperature will need to be boosted before it can be used in consumer devices. Neither of those problems seem like showstoppers, however.
Physicists have known about the amazing properties of graphene for a decade or so now. They’ve even predicted that it will take the world of microelectronics by storm. What nobody really appreciated was how quickly this would happen. Now we’re finding out.
Ref: arxiv.org/abs/1012.4415: Radio Frequency Electrical Transduction of Graphene Mechanical Resonators
