It was long thought impossible to obtain useful work from random fluctuations in a system in thermal equilibrium. In fact, in the 1960s, the famous American physicist Richard Feynman effectively halted further research after he argued in a series of lectures that the Brownian motion or the thermal motion of atoms could not do useful work.

Now, a new study published Physical Inspection E The article “Charging Capacitors from Thermal Oscillations Using a Diode” proved that Feynman had overlooked something important.

Three of the article’s five authors are employees of the University of Arkansas Department of Physics. According to first author Paul Thibadeau, his work clearly demonstrates that the thermal fluctuations of free-standing graphene connected to a circuit with non-linear resistive diodes and storage capacitors actually produce useful work by charging the storage capacitors.

The authors found that when the initial charge of the storage capacitors is zero, the circuit draws energy from the thermal environment to charge them.

The team then showed that the system satisfies both the first and second laws of thermodynamics throughout the charging process. They also found that larger storage capacitors provide more stored charge, while smaller graphene capacitance provides both a higher initial charge rate and a longer discharge time. These features are important because they allow time for the storage capacitors to disconnect from the energy harvesting circuit before the total charge is lost.

This latest publication builds on the group’s two previous studies. First published Physical Review Letters 2016. In this work, Thibadeau and his co-authors identified graphene’s unique vibrational properties and energy harvesting potential.

The latter was published in an article Physical Inspection E for 2020, where they discussed a plan using graphene that could provide clean, unlimited power for small devices or sensors. This latest research goes a step further by creating a mathematical design for a circuit that can harvest energy from the earth’s heat and store it in capacitors for later use.

“Theoretically, we wanted to prove that,” Thibadeau said. “There are well-known sources of energy such as kinetic, solar, ambient radiation, acoustic and thermal gradients. Now there is also non-linear thermal energy. People often think that thermal energy requires a temperature gradient. It is of course an important practical source of energy, but it has never existed before. “We discovered a new source of energy. And this new power doesn’t need two different temperatures because it exists at one temperature.”

In addition to Thibadeau, co-authors include Pradeep Kumar, John Noy, Surendra Singh and Luis Bonilla. Kumar and Singh are also at the University of Arkansas, the University of Neu California, Berkeley, and Bonilla Madrid III. He is a professor of physics at Carlos University.

The concept of non-linear thermal current. Credit: Ben Goodwin

Ten years of investigation

The research represents a solution to a problem Thibadeau has been working on for more than a decade; when he and Kumar first tracked the dynamic motion of ripples in free-standing graphene at the atomic level. Discovered in 2004, graphene is a one-atom-thick layer of graphite. The duo observed that free-standing graphene has a wavy structure, with each wave spinning up and down in response to ambient temperature.

“The thinner something is, the more flexible it is,” Thibadeau said. “And there’s nothing more flexible, just one atom thick. It’s like a trampoline that is constantly moving up and down. If you want to stop it moving, you have to cool it down to 20 Kelvin.”

Current efforts to develop this technology have focused on a device he calls the Graphene Energy Harvester (or GEH). GEH uses a negatively charged sheet of graphene suspended between two metal electrodes.

As the graphene spins upward, it creates a positive charge on the top electrode. As it rotates downward, it creates an alternating current, positively charging the lower electrode. With reverse connected diodes, separate paths are provided in the circuit, allowing current to flow in both directions, creating a pulsating DC current operating on the load resistor.

commercial programs

NTS Innovations company specializing in nanotechnology holds an exclusive license to turn GEH into commercial products. Because GEH circuits are so small, only nanometers in size, they’re ideal for bulk duplication on silicon chips. When multiple GEH circuits are placed on a chip in arrays, more power can be produced. They can also work in many environments, making them particularly attractive for wireless sensors in locations where battery replacement is cumbersome or expensive, such as underground piping systems or internal aircraft conduits.

Donald Meyer, founder and CEO of NTS Innovations, said: “Paul’s research reinforces our belief that we are on the right track with Graphene Energy Harvesting. We appreciate our partnership with the University of Arkansas in bringing this technology to market.”

“There is widespread demand in the electronics industry to reduce form factors and reduce reliance on batteries and wired power. We believe Graphene Energy Harvesting will have a profound impact on both,” said Ryan McCoy, vice president of sales and marketing, NTS Innovations.

Regarding the long journey to his latest theoretical breakthrough, Thibaudeau said, “The question was always: ‘If our graphene device is in a very quiet, very dark environment, does it collect energy or not?’ The generally accepted answer to this question is no, as it clearly defies the laws of physics. But physics has never been looked closely at.”

“I think people are a little scared because of Feynman. So everyone said, “I’m not touching him.” But this question has just demanded our attention. To be honest, it was only thanks to the persistence and divergent approach of our unique team that it was possible to find a solution.”