Pulling Energy Out Of Thin Air
During the middle ages, the concept of the perpetual motion machine would develop. The first law, known as the Law of Conservation of Energy, would prohibit the existence of a perpetual motion machine, by preventing the creation or destruction of energy within an isolated system.
In 1867 James Clerk Maxwell, the Scottish pioneer of electromagnetism, conceived of a thermodynamic thought experiment that exhibited a key characteristic of a thermal perpetual motion machine. Because faster molecules are hotter, the “beings” actions cause one chamber to warm up and the other to cool down, seemingly reversing the process of a heat engine without adding energy.
Despite maintaining the conservation of energy, both Maxwell’s demon and thermal perpetual motion machines, contravened, arguably one of the most unrelenting principles of thermodynamics. This inherent, natural progression of entropy towards thermal equilibrium directly contradicts the behavior of all perpetual motion machines of the second kind.
In 1827, Scottish botanist Robert Brown, while studying the fertilization of flowering plants, began to investigate a persistent, rapid oscillatory motion of microscopic particles that were ejected by pollen grains suspended in water. Called Brownian motion, this phenomenon was initially attributed to thermal convection currents within the fluid. However, this would soon be abandoned as it was observed that nearby particles exhibited uncorrelated motion. Furthermore, the motion was seemingly random and occurred in any direction.
These conclusions had led Albert Einstein in 1905 to produce his own quantitative theory of Brownian motion. And within his work, Brownian motion had indirectly confirmed the existence of atoms of a definite size. Brownian motion would tie the concepts of thermodynamics to the macroscopic world.
In 1900, Gabriel Lippman, inventor of the first color photography method, proposed an idea for a mechanical thermal perpetual motion machine, known as the Brownian ratchet. The device is imagined to be small enough so that an impulse from a single molecular collision, caused by random Brownian motion, can turn the paddle. The net effect from the persistent random collisions would seemingly result in a continuous rotation of the ratchet mechanism in one direction, effectively allowing mechanical work to be extracted from Brownian motion.
During the 1990s, using Brownian motion to extract mechanical work would re-emerge in the field of Brownian motor research. Brownian motors are nanomachines that can extract useful work from chemical potentials and other microscopic nonequilibrium sources.
In recent years, they’ve become a focal point of nanoscience research, especially for directed-motion applications within nanorobotics.
ELECTRICAL BROWNIAN MOTION
In 1950, french physicist Léon Brillouin proposed an easily constructible, electrical circuit analog to the Brownian ratchet. Much like the ratchet and pawl mechanism of the Brownian ratchet, the diode would in concept create a “one-way flow of energy“, producing a direct current that could be used to perform work. However, much like the Brownian ratchet, the “one-way” mechanism once again fails when the entire device is at thermal equilibrium.
In early 2020, a team of physicists at the University of Arkansas would make a breakthrough in harvesting the energy of Brownian Motion. Instead of attempting to extract energy from a fluid, the team exploited the properties of a micro-sized sheet of freestanding graphene. At room temperature graphene is in constant motion. The individual atoms within the membrane exhibit Brownian motion, even in the presence of an applied bias voltage.
The team created a circuit that used two diodes to capture energy from charge flow created by the graphene’s motion. In this state, the graphene begins to develop a low-frequency oscillation that shifts the evenly distributed power spectrum of Brownian motion to lower frequencies. The diodes had actually amplified the power delivered, rather than reduce it, suggesting that electrical work was done by the motion of the graphene despite being held at a single temperature. Despite contradicting decades of philosophical analysis, the team behind this experiment concluded that while the circuit is at thermal equilibrium, the thermal exchange between the circuit and its surrounding environment is in fact powering the work on the load resistor.
Graphene power generation could be incorporated into semiconductor products, providing a clean, limitless, power source for small devices and sensors.
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