Credit: AlexanderAlUS/Wikipedia/CC BY-SA 3.0
Credit: AlexanderAlUS/Wikipedia/CC BY-SA 3.0
It has long been considered impossible to obtain useful work from random fluctuations in a system at thermal equilibrium. Indeed, in the 1960s, the eminent American physicist Richard Feynman effectively shut down further inquiry after he argued in a series of lectures that Brownian motion, or the thermal motion of atoms, could not do useful work.
Now, a new study has been published in physical review e Titled “Charging Capacitors from Thermal Fluctuations Using Diodes” proved that Feynman had missed something important.
Three of the paper’s five authors are from the University of Arkansas Department of Physics. According to first author Paul Thibado, their study rigorously demonstrates that thermal fluctuations of freestanding graphene, when connected to a circuit with nonlinear resistance diodes and storage capacitors, produce useful work by charging the storage capacitors.
The authors found that when storage capacitors have zero initial charge, the circuit draws energy from the thermal environment to charge it.
The team then showed that the system complied with the first and second laws of thermodynamics during the charging process. They also found that larger storage capacitors produce more stored charges and that smaller graphene capacitances provide a higher initial charge rate and longer discharge time. These properties are important because they allow time for the storage capacitors to separate from the energy collector circuit before net charge is lost.
This latest publication builds on two of the group’s previous studies. The first was published in 2016 Physical review letters. In that study, Thibadeaux and colleagues identified the unique vibrational properties of graphene and potential for energy harvesting.
The second was published in 2020 physical review e The article where they discuss a circuit using graphene that can provide unlimited clean power to small devices or sensors.
This latest study goes one step further by creating a mathematical design for a circuit capable of harvesting energy from the Earth’s heat and storing it in capacitors for later use.
“Theoretically, that was what we set out to prove,” Tibado explained. “There are known sources of energy, such as kinetic, solar, ambient radiation, acoustic and thermal gradients. Now there is also nonlinear thermal energy. Usually, people imagine that thermal energy requires a temperature gradient. That of course is, is an important source of practical energy, but What we found is a new source of energy that didn’t exist before. And this new energy doesn’t require two different temperatures because it exists at one temperature.”
In addition to Thibado, co-authors include Pradeep Kumar, John Niu, Surendra Singh, and Louis Bonilla. Kumar and Singh are professors of physics at the University of Arkansas and New York at the University of California, Berkeley, and Bonilla with University Carlos III in Madrid.
decade of inquiry
The study represents the solution to a problem Thibado has been studying for more than a decade, when he and Kumar tracked the dynamic motion of ripples in freestanding graphene at the atomic level. Discovered in 2004, graphene is a sheet one atom thick of graphite. The duo noticed that free-standing graphene has a wavy structure, with each ripple flipping up and down in response to the ambient temperature.
“The thinner the thing, the more flexible it is,” said Tibadoux. “And just one atom thick, there is nothing more elastic. It’s like a trampoline, constantly moving up and down. If you want to keep it from moving, you have to cool it down to 20 K.”
His current efforts to develop this technology focus on building a device he calls the Graphene Energy Harvester (or GEH). GEH uses a sheet of negatively charged graphene suspended between two metal electrodes.
When graphene is inverted, it generates a positive charge at the top electrode. When flipped down, it positively charges the bottom electrode, creating an alternating current. With diodes wired in reverse, allowing current to flow in both directions, separate paths are provided through the circuit, resulting in a pulsed DC current that does work on the load resistor.
NTS Innovations, a nanotechnology company, holds the exclusive license to develop GEH into commercial products. Because GEH circuits are so small, nanometer in size, they are ideal for mass copying on silicon wafers. When multiple GEH circuits are included on a chip in arrays, more power can be produced. They can also operate in many environments, making them particularly attractive to wireless sensors in locations where changing batteries is inconvenient or costly, such as in an underground piping system or aircraft interior cable ducts.
“Paul’s research reinforces our conviction that we are on the right track with Graphene Energy Harvesting,” said Donald Meyer, founder and CEO of NTS Innovations. “We value our partnership with the University of Arkansas in bringing this technology to market.”
Ryan McCoy, Vice President of Sales and Marketing at NTS Innovations added, “There is a widespread demand in the electronics industry to shrink form factors and reduce reliance on batteries and wired power. We believe that Graphene Energy Harvesting will have a profound impact on both.”
“There was always this question: ‘If our graphene device is in a really quiet, dark environment, will it harvest any energy or not?’” Thibadeau said of the long road to his latest theoretical breakthrough. The traditional answer to that is no, because it seems to defy the laws of physics. But physics hasn’t been looked at carefully.
“I think people were afraid of the topic a little bit because of Feynman. So, everyone just said, ‘I don’t dwell on that. ‘ But the question kept demanding our attention. Frankly, its solution was found only through the perseverance and diverse methods of our unique team.”
PM Thibado et al, Charging capacitors from thermal fluctuations using diodes, physical review e (2023). DOI: 10.1103/PhysRevE.108.024130
“Web maven. Infuriatingly humble beer geek. Bacon fanatic. Typical creator. Music expert.”