At room temperature, micron-sized sheets of freestanding graphene are in constant motion, even in the presence of an applied bias voltage. University of Arkansas researchers collecting the displacement current using a nearby small-area metal electrode and present an Ito-Langevin model for the motion coupled to a circuit containing diodes. Numerical simulations show that the system reaches thermal equilibrium and the average rates of heat and work provided by stochastic thermodynamics tend quickly to zero. Power is dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath. The exact power formula is similar to Nyquist’s noise power formula, except that the rate of change of diode resistance significantly boosts the output power, and the movement of the graphene shifts the power spectrum to lower frequencies. They have calculated the equilibrium average of the power by asymptotic and numerical methods. Experiments have proven the theory.
NOTE: These are big claims and the power levels must be very, very small. They will need millions of miniaturized circuits powering a capacitor to replace the battery for a tiny low power chip.
Harvesting energy from graphene is controversial because it disproves physicist Richard Feynman’s assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado’s team found that at room temperature the thermal motion of graphene does induce an alternating current (AC) in a circuit, an achievement thought to be impossible.
Thibado’s group built their circuit with two diodes for converting AC into a direct current (DC). The diodes in opposition let current to flow both ways. There are separate paths through the circuit which produce a pulsing DC current that performs work on a load resistor.
On-off, switch-like behavior of the diodes amplifies the power delivered. It was previously expected to reduce power.
The power is not from heat differences as this would violate the second law of thermal dynamics.
The next goal is to store the energy in capacitors for later use. They need to miniaturize 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.
SOURCES- University of Arkansas, Physical Review E – Fluctuation-induced current from freestanding graphene
Written By Brian Wang, Nextbigfuture.com