Scientists solve the mystery of magnetic levitation beyond classical physics

Scientists from the Technical University of Denmark (DTU) have confirmed the basic physics of the newly discovered magnet levitation phenomenon.

In 2021, a scientist from Turkey published a paper detailing an experiment in which a magnet was attached to a motor, causing it to spin rapidly. When this setup was brought close to a second magnet, the second magnet began to rotate and suddenly hovered in a fixed position a few centimeters away.

While magnetic levitation is nothing new — perhaps the most famous example are maglev trains that rely on a strong magnetic force for lift and propulsion — the experiment has puzzled physicists because the phenomenon has not been described in classical physics, or at least in any classical physics. Known mechanism of magnetic levitation.

Magnetic levitation is demonstrated using a Dremel tool rotating a magnet at a frequency of 266 Hz. The size of the rotating magnet is 7 x 7 x 7 mm3 and the floating magnet is 6 x 6 x 6 mm3. This video demonstrates the physics described in the paper. Credit: DTU.

However, it is now. Rasmus Björk, a professor at DTU Energy, was fascinated by Okkar's experiment and set out to replicate it with master's student Joachim M. Hermansen while finding out exactly what was happening. Replication was easy and could be done with off-the-shelf components, but its physics were strange, says Rasmus Björk:

“Magnets shouldn't hover when they're close together. Usually they attract or repel each other. But if you spin one of the magnets, it turns out you can achieve this levitation. And that's the weird part. The force on the magnets shouldn't change just because “You rotate one of them, so there seems to be a coupling between motion and magnetic force.”

The results were recently published in the journal Applied physics review.

Several experiments to confirm the physics

The experiments involved several magnets of different sizes, but the principle remained the same: by rotating a magnet very quickly, the researchers observed how another magnet nearby, called a “floating magnet,” began to rotate at the same speed while quickly sticking to a position where it remained. Swirling.

They found that when the floating magnet is held in position, it is oriented close to the axis of rotation and toward the pole similar to the rotating magnet. So, for example, the shadow of the north pole of the floating magnet, as it rotates, points to the north pole of the fixed magnet.

This is different from what would be expected based on the laws of static magnetism, which explain how a static magnetic system works. However, as it turns out, it is precisely the static magnetic interactions between the rotating magnets that are responsible for creating the equilibrium position of the floats, as found by co-author and doctoral student Frederick L. Dorhus using a simulation of this phenomenon. They observed a significant effect of magnet size on hover dynamics: smaller magnets require higher rotational speeds for lift due to their greater inertia and the higher they fly.

“It turns out that the floating magnet wants to line up with the rotating magnet, but it can't spin fast enough to do so. As long as this coupling is maintained it will hover or levitate,” says Rasmus Bjork.

“You can compare it to a spinning top. It will only stand up if it is spinning but is fixed in position by its rotation. Only when the rotation loses energy does the force of gravity – or in our case the push and pull of a magnet – become large enough to overcome equilibrium.”

Reference: “Alternating Magnetic Levitation” by Joachim Marko Hermansen, Frederik Laust-Dorhus, Kathrin Frandsen, Marco Piligia, Christian R.H. Bahl, and Rasmus Björk, 13 October 2023, Physical review was applied.
DOI: 10.1103/PhysRevApplied.20.044036