Guest essay by Eric Worrall
A meme has started circulating on the internet about graphene batteries providing unlimited free energy, harvested from the random Brownian Motion of the graphene. But there is another possible explanation, which the researchers may have overlooked.
Physicists Just Showed That Graphene Circuits Can Produce Clean, Limitless Power
6 OCTOBER 2020
Scientists have been able to draw power from the thermal motion of graphene at room temperature, potentially giving us a clean future source of limitless energy for small devices.
The approach cleverly harnesses both the nanometre-sized rippling and the Brownian motion – random movement of particles – found in graphene, producing an electric current that could be put to a variety of uses.
“An energy-harvesting circuit based on graphene could be incorporated into a chip to provide clean, limitless, low-voltage power for small devices or sensors,” says physicist Paul Thibado, from the University of Arkansas.
The research draws on previous work from the same lab, in which freestanding graphene was shown to ripple and buckle in a way that could be harvested for energy.
“The origin of these nanometre-sized ripples is still an open question,” the team writes in their study, noting that the graphene ripple seems to stem from subatomic particle interactions in the material.
A crucial part of the development of their system was using two diodes in the circuit to convert the original alternating current (AC) into direct current (DC). This allowed the current to flow both ways through the circuit, along separate paths.
…Read more: https://www.sciencealert.com/physicists-build-a-circuit-from-graphene-that-generates-clean-limitless-power
The abstract of the paper;
Fluctuation-induced current from freestanding graphene
P. M. Thibado, P. Kumar, Surendra Singh, M. Ruiz-Garcia, A. Lasanta, and L. L. Bonilla
Phys. Rev. E 102, 042101 – Published 2 October 2020
At room temperature, micron-sized sheets of freestanding graphene are in constant motion, even in the presence of an applied bias voltage. We quantify the out-of-plane movement by collecting the displacement current using a nearby small-area metal electrode and present an Ito-Langevin model for the motion coupled to a circuit containing diodes. Numerical simulations show that the system reaches thermal equilibrium and the average rates of heat and work provided by stochastic thermodynamics tend quickly to zero. However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath. The exact power formula is similar to Nyquist’s noise power formula, except that the rate of change of diode resistance significantly boosts the output power, and the movement of the graphene shifts the power spectrum to lower frequencies. We have calculated the equilibrium average of the power by asymptotic and numerical methods. Excellent agreement is found between experiment and theory.Read more (paywalled): https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.042101
The researchers provided the following video simulation of their device;
Unfortunately nobody put a big sheet of graphene in my Santa sock, so I cannot test one of these free energy batteries for myself, and I don’t have access to the full paper.
But as an amateur electronics enthusiast, something immediately jumped out at me. The description of the physical structure of their graphene “battery” looks a lot like a resonant circuit.
If you touch one terminal of an oscilloscope, or a very sensitive volt meter, the device consistently registers a small AC voltage in your body. This electric field in your body is induced by fields created by the electric wires in the walls, the devices in the room, and the power lines in the street.
Other sources also contribute in a small way. The sun emits a lot of radio waves, as does commercial radio, TV, satellites, mobile phones, computers – there is a long list of potential sources.
This stray voltage is harmless to people, undetectable except with sensitive electronic equipment. But in larger structures the induced electric field can be significant. It can even cause severe damage to metal framed buildings, by triggering electrolytic corrosion.
Sensitive resonant circuits can amplify these tiny electric fields, allowing the oscillating electric field to build until the voltage is sufficient to overcome the voltage drop of the rectifier diode, and deposit a packet of charge into their capacitor (see the simulation above). This is the principle of operation of a crystal radio.
Crystal radios are primitive radio receivers which draw the electricity required to operate them from the received radio signal.
If you look at the circuit diagram of a crystal radio (below), it looks remarkably similar to the circuit of the brownian motion battery described in the video (above).
It is not clear from the abstract whether the scientists attempted to shield their graphene batteries from these ubiquitous stray external electric fields, and I do not have access to the full paper. But even if they made an attempt to shield their battery, I’m more inclined to believe that what the researchers accidentally built was very sensitive stray radio voltage detector, rather than a miraculous violation of the second law of thermodynamics.
How could scientists test whether their “battery” is really just a sensitive receiver of ambient radio signals? Very simple. Try attaching an antenna and ground, like the crystal radio circuit above, and see if their free energy device picks up a stronger signal.
Update (EW): Peta of Newark suggests an even simpler explanation, acoustic vibrations – they built an electret microphone.