An energy-harvesting circuit based on graphene

Circuit that generates clean, limitless power from graphene

Physicists from the University of Arkansas have developed a circuit that generates clean, limitless power from graphene. By capturing graphene’s thermal motion, the circuit converts it into an electrical current.

The circuit could be incorporated into a chip to provide clean, limitless, low-voltage power for small devices or sensors.

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

Scientists 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.

Paul Thibado, professor of physics and lead researcher in the discovery, said, “We discovered that the design increased the amount of power delivered. We also found that the on-off, switch-like behavior of the diodes amplifies the power delivered, rather than reducing it, as previously thought. The rate of change in the resistance provided by the diodes adds an extra factor to the power.”

Using a relatively new physics field, scientists proved the diodes increased the circuit’s power.

Coauthor Pradeep Kumar, associate professor of physics, said, “In proving this power enhancement, we drew from the emergent field of stochastic thermodynamics and extended the nearly century-old, celebrated theory of Nyquist.”

“the graphene and circuit share a symbiotic relationship. Though the thermal environment is performing work on the load resistor, the graphene and circuit are at the same temperature, and heat does not flow between them.”

Thibado said, “That’s an important distinction, because a temperature difference between the graphene and circuit, in a circuit producing power, would contradict the second law of thermodynamics. “This means that the second law of thermodynamics is not violated, nor is there any need to argue that ‘Maxwell’s Demon’ is separating hot and cold electrons.”

Scientists also discovered that graphene’s relatively slow motion induces a current in the circuit at low frequencies, which is essential from a technological perspective because electronics function more efficiently at lower frequencies.

Thibado explained, “People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. If no current were flowing, the resistor would cool down. What we did was reroute the current in the circuit and transform it into something useful.”

In the future, scientists will examine whether DC can be stored in a capacitor for later use, a goal that requires miniaturizing the circuit and patterning 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 a low-power battery replacement.

The findings are published in the journal Physical Review E.

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