Physicists Build Circuit that Generates Clean, Limitless Power from Graphene
A research team at the University of Arkansas has successfully created a circuit capable of capturing the thermal motion of graphene, and turning it into an electrical current.
“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,” said Paul Thibado, lead researcher in the discovery.
The recently published findings prove a theory, developed three years ago, that freestanding graphene – a single layer of carbon atoms – ripples and buckles in a way that shows promise for energy harvesting.
The theory of harvesting energy from graphene is controversial because it refutes the well known claim of physicist Richard Feynman that the thermal motion of atoms, known as Brownian motion, cannot work. Thibado's team found that the thermal motion of graphene actually induces an alternating current (AC) in a circuit at room temperature, an achievement considered impossible.
In the 1950s, physicist Léon Brillouin published groundbreaking work refuting the notion that the solution to harvesting energy from Brownian motion is to connect a single diode, a one-way electrical gate, to a circuit. Equipped with this knowledge, Thibado's team designed their circuit using two diodes to transform 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, generating a pulsing DC current that performs work on a load resistor.
Additionally, they found that their design increased the amount of power delivered. "We also found that the on-off, switch-like behaviour of the diodes actually amplifies the power delivered, rather than reducing it, as previously thought," said Thibado. "The rate of change in resistance provided by the diodes adds an extra factor to the power."
The team also discovered that the relatively slow motion of graphene induces current in the circuit at low frequencies, which is important from a technological perspective, as electronics function more efficiently at lower frequencies.
"People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down," Thibado explained. "What we did was re-route the current in the circuit and transform it into something useful."
The team's next objective is to determine if the DC current can be stored in a capacitor for later use, a goal that requires miniaturising the circuit and patterning it on a silicon wafer, or chip. If millions of these tiny circuits could be built onto a 1 mm x 1 mm chip, they could serve as a low-power battery replacement.
Learn more about the findings in this video.