Tiny membrane converts radio waves to light:
They bounce a laser beam of a DC biased capacitor that vibrates at its mechanical resonance when hit by radio waves. The new device has a room-temperature sensitivity of 100 pV Hz\u20131/2 for radio waves at 1 MHz. That sensitivity could be improved by a factor 20 they say.
Sure, 100pV/rtHz sounds impressive, but in the absence of any specified impedance or power level, it doesn't mean anything. I'd have to think it through, but at first glance its noise temperature is at best equal to the membrane temperature, which is ordinary room temperature. Tried and true semiconductor- based circuitry can better that easily.
Jeroen Belleman
"Jeroen Belleman"
** But with what size antenna ?Far as I can see, the device is glorified a condenser mic with laser light detection.
Gee, I bet " laser microphones " would sell like hot cakes to audiophools.
... Phil
People have been making laser microphones for years and years, and before that, folks including yours truly were doing the same thing to sense cantilever vibration in attractive-force microscopes.
You can easily see the thermal vibration of the membrane with a laser.
The noise temperature of a capacitor microphone is much larger than that of the active device because of the big capacitive voltage divider at the input.
Cheers
Phil
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I don't think we're on the same wavelength, so to speak. The title of their article in Nature is more explicit: "Optical detection of radio waves through a nanomechanical transducer".
They apply an electrical signal to a tiny DC-biased capacitor with one movable plate and detect its movement by shining a laser at it. Trying to detect the signal as if this was a capacitor microphone sort of defeats the purpose.
I still think it's silly. I could be wrong.
I haven't read the paper yet. Just skimming over it, I see unfamiliar terms like 'cooperativity'.
Jeroen Belleman
I think there are thermodynamic issues as well. The free resonance will have an equilibrium excitation of kT/2, so if they sharpen up the resonance to increase the signal, they also increase the noise.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
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