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.
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.
We report radio frequency (rf) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ~ 34 MHz, quality factor ~ 10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
Various problems will have to be ironed out. 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.
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