[Apr. 5, 2023: Bob Whitby, University of Arkansas]
Physics professor Paul Thibado with samples of energy-harvesting chips under development. (CREDIT: University of Arkansas)
A team of physicists from the University of Arkansas has successfully developed a circuit capable of capturing the thermal motion of graphene and converting it into electric current.
“A graphene-based energy-harvesting circuit could be integrated into a chip to provide clean, unlimited low-voltage power to small devices or sensors,” said Paul Thibado, professor of physics and lead researcher in the discovery.
The conclusions, entitled “Autonomous Graphene Fluctuation Induced Current” and published in the journal Physical examination Eare proof of a theory physicists developed at the U of A three years ago that free-standing graphene – a single layer of carbon atoms – ripples and warps in a way that holds promise for recovery of energy.
The idea of harvesting energy from graphene is controversial because it disproves physicist Richard Feynman’s well-known assertion that thermal motion of atoms, known as Brownian motion, cannot work. Thibado’s team discovered that at room temperature, the thermal motion of graphene actually induces alternating current (AC) in a circuit, an achievement previously thought impossible.
In the 1950s, physicist Léon Brillouin published a landmark paper disproving the idea that adding a single diode, a one-way electric gate, to a circuit is the key to harvesting energy from Brownian motion. Knowing this, Thibado’s group built their circuit with two diodes to convert alternating current to direct current (DC). With the diodes in opposition allowing current to flow in both directions, they provide separate paths through the circuit, producing a pulsating direct current that performs work on a load resistor.
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Additionally, they found that their design increased the amount of energy delivered. “We also found that the on-off, switch-like behavior of the diodes actually amplifies the power output, rather than reducing it, as previously thought,” Thibado said. “The rate of change in resistance provided by the diodes adds an additional factor to the power.”
The team used a relatively new area of physics to prove that diodes increased circuit power. “In proving this power enhancement, we drew on the emerging field of stochastic thermodynamics and extended the famous, nearly century-old Nyquist theory,” said co-author Pradeep Kumar, associate professor of physics. and co-author.
Graphene Chip Test – A sample energy harvesting chip being tested. (CREDIT: University of Arkansas)
According to Kumar, graphene and the circuit share a symbiotic relationship. Although the thermal environment does work on the load resistance, the graphene and the circuit are at the same temperature and heat does not flow between the two.
This is an important distinction, Thibado said, because a temperature difference between graphene and the circuit, in a power-generating circuit, would contradict the second law of thermodynamics.
Graphene chip – A sample energy harvesting chip under development. (CREDIT: University of Arkansas)
“This means that the second law of thermodynamics is not violated, and there is no need to assert that ‘Maxwell’s demon’ separates hot and cold electrons,” Thibado said.
The team also discovered that the relatively slow motion of graphene induces a current in the circuit at low frequencies, which is important from a technological perspective because electronics work more efficiently at low frequencies.
STM datasets acquired when the STM tip is not tunneling electrons. (a) Current through diode 2 as a function of time for the voltages. (CREDIT: PHYSICAL EXAM E)
“People may think that current flowing through a resistor causes it to heat up, but Brownian current does not. In fact, if no current was flowing, the resistor would cool,” Thibado explained. is to redirect the current in the circuit and turn it into something useful.”
The team’s next goal is to determine if direct current can be stored in a capacitor for later use, a goal that requires miniaturizing the circuit and modeling it on a silicon wafer or chip. If millions of these tiny circuits could be built on a 1 millimeter by 1 millimeter chip, they could serve as low-power battery replacements.
Comparison of numerical theory, approximate asymptotic theory and STM experiments. (CREDIT: PHYSICAL EXAM E)
The University of Arkansas holds multiple patents pending in the United States and international markets on the technology and has licensed it for commercial applications through the university’s Technology Ventures division.
Researchers Surendra Singh, university professor of physics; Hugh Churchill, associate professor of physics; and Jeff Dix, assistant professor of engineering, contributed to the work, which was funded by the Chancellor’s Commercialization Fund supported by the Walton Family Charitable Support Foundation.
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Note: The documents provided above by University of Arkansas. Content may be edited for style and length.
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