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In Fluctuation-induced current from freestanding graphene (peer-reviewed version on Phys. Rev. E, note: behind a paywall) Thiabado, et al, report the extraction of work from brownian motion. The experimental set up involves graphene in close but insulated contact with an electrode that charges a battery and a storage capacitor until a switch shunts the potential through a resistor. enter image description here

This seems to be a Feynman-Smoluchowski ratchet hence perpetual motion of the second kind. If so, where is the flaw in the experiment?

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Thibado "published" about this idea three years ago https://researchfrontiers.uark.edu/good-vibrations/ enter image description here https://youtu.be/wrleMqm3HiU

He now added complications (diodes etc) but that won't help.

The system with mechanical noise makes it a bit more complicated but not really different from a resistor with thermal noise. It is like trying to get energy from the thermal voltage of a resistor. Cannot be done.

Edit: there is an obvious source of energy in the schematic of their new preprint: that battery. I suspect that the bias voltage is the source of the power that they detect. (But I have not analyzed this in detail.)

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  • $\begingroup$ Could you expand your answer a bit? You've provided a bit of relevant history but not provided a critique of the experiment except by assertion. $\endgroup$ Oct 4, 2020 at 15:15
  • $\begingroup$ @JamesBowery It is a preprint, uploaded in February. Does not seem to have passed peer-review (and I would not be qualified although I published about the graphite surface). But I would look with some suspicion at that bias voltage. Most likely that is the source of the energy - it could not be the graphene. $\endgroup$
    – user137289
    Oct 4, 2020 at 16:50
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    $\begingroup$ I'll wait a while before accepting your answer in the event someone qualified weighs in. In the interim, could you add your suspicion to your answer? Thanks. $\endgroup$ Oct 4, 2020 at 19:02
  • $\begingroup$ @Pieter the paper has passed peer review and it's published in PRE $\endgroup$
    – fqq
    Oct 20, 2020 at 0:12
  • $\begingroup$ I compared the published version, did not see significant changes. But my opinion this is in principle still the same thing as connecting two resistors to each other: when they are at the same temperature, the power from thermal voltages in the left one and dissipated in the other one is the same as the other way around. The difference is that this is a mechanical source and that its thermal noise is not white Gaussian noise. $\endgroup$
    – user137289
    Oct 20, 2020 at 8:28
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The interpretation is almost certainly wrong. A graphene film cannot "ripple" due to a static, spatially uniform temperature. It can only mechanically deform in response to a changing temperature or a temperature gradient. If all the calculations are done properly, the graphene film device will be determined to be a heat engine whose performance is consistent with the usual laws of thermodynamics. I can't state that from direct evidence (i.e., an experiment that measures temperature and entropy changes associated with this device), but the indirect evidence is overwhelming.

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  • $\begingroup$ Is this animation of graphene thermal vibration inaccurate? youtube.com/watch?v=OoKDC1AMMwg $\endgroup$ Oct 4, 2020 at 0:28
  • $\begingroup$ Probably not inaccurate. But think of this as waves on the ocean. There are machines that extract energy from waves, but they do not violate the laws of thermodynamics. $\endgroup$
    – S. McGrew
    Oct 4, 2020 at 1:18
  • $\begingroup$ Note that mechanical energy can often be converted to electrical energy with nearly 100% efficiency; but converting thermal energy to mechanical energy or electrical energy is limited by the laws of thermodynamics. $\endgroup$
    – S. McGrew
    Oct 4, 2020 at 1:35
  • $\begingroup$ That video's caption reads: "Atom vibration within graphene is shown in equilibrium at ambient condition (300 K and 1 atm)." This doesn't seem analogous to an ocean's surface, the surface waves of which are not in equilibrium. $\endgroup$ Oct 4, 2020 at 4:52
  • $\begingroup$ There are vibrational modes on a graphene sheet at finite temperatures. Nothing strange with that. But one cannot extract energy from that (second law of thermodynamics). $\endgroup$
    – user137289
    Oct 4, 2020 at 12:34

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