Invention of a device which pulls electricity directly from Earth's rotation
Scientists in the US have built a small device which seems to pull electrical energy from Earth’s rotation itself. The table top experiment produced only tens of microvolts. In a controversial experiment, physicists investigated whether we could harness the Earth's rotational energy to generate electricity. In a controversial experiment, a team of physicists investigated whether we could harness the Earth’s rotational energy to generate electricity. It’s a deceptively simple idea that researchers have only started to grapple with over the last decade. But whether the concept will ever turn into a feasible source of renewable energy remains to be seen, with the team’s peers noting their scepticism of the results. The team carried out the work in New Jersey with colleagues from NASA’s Jet Propulsion Laboratory. Their results hint that Earth’s spin and magnetic field could someday act as a constant, fuel-free energy source, if the effect scales up. Their experiment had a "controversial but intriguing" result.
The work was led by Christopher F. Chyba, the Dwight D. Eisenhower Professor of International Affairs and astrophysical sciences at Princeton University. The team aligned a special device made up of a weak manganese-zinc ferrite conductor and electrodes at each end, at a 57 angle, making it perpendicular to our planet’s rotational motion and its magnetic field. They observed that the device generated 17 microvolts of electricity, which as Nature points out is a fraction of the voltage released by a single neuron firing. The research explores how electromagnetic theory, the rules describing electric and magnetic forces, connects to energy and planetary environments. The earth is wrapped in a geomagnetic field, the magnetic bubble around Earth created by moving metal in its outer core. As the planet spins, that field stays mostly fixed in space, so any conductor attached to Earth moves through it all the time.
It’s a “controversial but intriguing” result, as researchers said, especially considering the minuscule voltage is extremely difficult to isolate from other physical influences. “The idea is somewhat counter-intuitive and has been argued since Faraday,” University of Wisconsin–Eau Claire emeritus physicist Paul Thomas, who wasn’t involved in the research, said. For decades, standard arguments in physics said that any voltage created this way would instantly disappear as electrons shifted to cancel the effect. The researchers pointed out a loophole, showing that a specially shaped conductor might avoid that cancellation. The idea focused on a magnetically responsive shell which bends field lines while remaining a poor electrical conductor. Such a structure could, on paper, keep Earth’s magnetic push from being completely balanced by the usual static charges. At the heart of all of this is the Lorentz force, the rule that charges feel in electric and magnetic fields. When a conductor moves through a magnetic field, this force pushes electrons sideways and can, in principle, create a voltage around the circuit. Normally, the electrons slide only a tiny distance before their own electric field cancels the magnetic push, so the current quickly dies away. This cancellation happens in a short time, less than a billionth of a second, so Earth’s rotation seems useless as a power source. The trick in this new device is to choose a shape and material where that perfect cancellation cannot happen everywhere inside the conductor. The requirement shows up in a low magnetic Reynolds number, a measure of how easily magnetic fields slip through a moving conductor. In this view, Earth’s magnetic field helps transfer a minute amount of rotational energy into the ferrite cylinder. The planet very slightly slows while the device gains an equally tiny amount of electrical energy, keeping the total energy and angular momentum balanced.
Retired physicist Rinke Wijngaarden, who found the effect didn’t work in his own 2018 experiments added that he’s “still convinced that the theory of Chyba et al. cannot be correct.” In the lab, that abstract shell became a hollow cylinder of about 1 foot long. The team made it from manganese zinc ferrite, a ceramic material which guides magnetic fields but barely conducts electricity. They aimed the cylinder roughly north to south and tilted it so the long axis sat at about 57 degrees. In that orientation, it stayed perpendicular to both Earth’s rotation at Princeton’s latitude and the surrounding magnetic field. Electrodes at each end let the researchers measure a constant voltage between the two faces of the cylinder as Earth turned. In their runs, the system generated tens of microvolts and its voltage reversed when they rotated the setup, matching the prediction. A solid cylinder made of the same ferrite, with no hollow shell, produced no measurable voltage at any orientation. Another shell designed so that magnetic diffusion, the slow spreading of magnetic fields in a conductor, did not matter also stayed quiet.
The device could theoretically work by having the generator pass through the Earth’s magnetic field, parts of which remain static, producing a current. However, electrons could end up rearranging themselves as a result to create an opposing force, negating the effect. Because the voltages were too small, the group ran its main experiments in a dark underground room with very low electrical noise. They later repeated the measurements in a residential building about 3.5 miles away, where interference made the data noisier but showed the same behaviour. One subtle background effect was the Seebeck effect, in which a temperature difference along a material creates its own voltage. To handle this, the researchers constantly monitored temperatures at both ends of the cylinder and subtracted the expected Seebeck signal from their measurements. When the cylinder pointed in its first orientation, the device produced a steady voltage close to the value predicted by the theory. Turned 180 degrees, the voltage kept the same magnitude but flipped sign, while at 90 and 270 degrees it dropped to nearly zero. By switching their meter into current mode, they also saw a steady direct current of only tens of nano-amps. Even so, that product of voltage and current is many millions of times smaller than the power used by everyday electronics.
Chyba and his team claim to have corrected for this by coming up with a special material that isn’t prone to rearranging itself in this way by maintaining the same electrostatic force inside the device. In short, plenty of research has yet to be done before we can definitively say that we could harness the Earth’s rotational energy to generate power. But the team of physicists is planning to do just that, attempting to scale up their experiment to generate an actually useful amount of energy. Despite the excitement around the idea, the researchers stress that the work is still a very early step. There are also formal critiques which argue the basic scheme cannot work, and the debate continues. If the effect holds up and can be scaled, future devices might power sensors or scientific instruments without any refuelling needed. The team even suggests that many small cylinders could be wired together, so that the voltages add up to something more useful. For now, the most important next step is clear, an independent group must build a similar device and test the idea. “The first thing that needs to happen is that some independent group needs to reproduce, or rebut, our results,” said Chyba. Intriguingly, assuming that the system would work and would be scaled up to meet the demands of the entire planet, the Earth’s rotational spin would only slow by seven milliseconds over the next 100 years, the researchers found, which is in the same ballpark as the amount the Moon’s pull slows the Earth’s rotation over the same period in future.
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