Energy harvesting circuit captures graphene's thermal motion

October 08, 2020 // By Rich Pell
Energy harvesting circuit captures graphene's thermal motion
Physicists at the University of Arkansas say they have successfully developed a circuit capable of capturing graphene's thermal motion and converting it into an electrical current.

The discovery, say the researchers, is proof of a theory they developed three years ago that freestanding graphene - a single layer of carbon atoms - ripples and buckles in a way that holds promise for energy harvesting.

"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 Paul Thibado, professor of physics and lead researcher in the discovery.

The idea of harvesting energy from graphene is controversial, say the researchers, because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Instead, the researchers found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit - an achievement thought to be impossible.

In the 1950s, physicist Léon Brillouin published a landmark paper refuting the idea that adding a single diode - a one-way electrical gate - to a circuit is the solution to harvesting energy from Brownian motion. Knowing this, the researchers built their circuit with two diodes for converting AC into a direct current (DC). With the diodes in opposition allowing the current to flow both ways, they provide separate paths through the circuit, producing a pulsing DC current that performs work on a load resistor.

In addition, they say, they discovered that their design increased the amount of power delivered.

"We also found that the on-off, switch-like behavior of the diodes actually amplifies the power delivered, rather than reducing it, as previously thought," says Thibado. "The rate of change in resistance provided by the diodes adds an extra factor to the power."

To prove the diodes increased the circuit's power, the researchers used a relatively new field of physics.

"In proving this power enhancement," says coauthor of a paper of the work Pradeep Kumar, associate professor of physics and coauthor, "we drew from

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