Scientists from the Technical University of Denmark (DTU) have confirmed the underlying physics of a newly discovered phenomenon of magnet levitation.
In 2021, a scientist from Turkey published a research paper detailing an experiment where a magnet was attached to a motor, causing it to rotate rapidly. When this setup was brought near 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 – the best-known example is probably Maglev trains that rely on a strong magnetic force for lift and propulsion – the experiment puzzled physicists as this phenomenon was not described by classical physics, or, at least, by any of known mechanism of magnetic levitation.
Magnetic levitation demonstrated using a Dremel tool spinning a magnet at 266 Hz. The rotor magnet is 7x7x7 mm3 and the floater magnet is 6x6x6 mm3. This video shows the physics described in the research. Credit: DTU.
It is now, however. Rasmus Bjørk, a professor at DTU Energy, was intrigued by Ucar’s experiment and set out to replicate it with MSc student Joachim M. Hermansen while figuring out exactly what was going on. The replicating was easy and could be done by using off-the-shelf components, but the physics of it was strange, says Rasmus Bjørk:
“Magnets should not hover when they are close together. Usually, they will either attract or repel each other. But if you spin one of the magnets, it turns out, you can achieve this hovering. And that is the strange part. The force affecting the magnets should not change just because you rotate one of them, so it seems there is a coupling between the movement and the magnetic force,” he says.
The results have recently been published in the journal Physics Review Applied.
Several experiments to confirm the physics
The experiments involved several magnets of differing sizes, but the principle remained the same: By rotating a magnet very fast the researchers observed how another magnet in close proximity, dubbed a “floater magnets,” started spinning at the same speed while it quickly locked into a position where it stayed hovering.
They found that as the floater magnet locked into position, it was oriented close to the axis of rotation and towards the like pole of the rotor magnet. So, for instance, the north pole of the floater magnet, while it was spinning, stayed pointing towards the north pole of the fixed magnet.
This is different from what was expected based on the laws of magnetostatics, which explain how a static magnetic system functions. As it turns out, however, the magnetostatic interactions between the rotating magnets are exactly what is responsible for creating the equilibrium position of the floater, as co-author PhD-student Frederik L. Durhuus found using simulations of the phenomenon. They observed a significant impact of magnet size on levitation dynamics: smaller magnets required higher rotation speeds for levitation due to their larger inertia and the higher it would float.
“It turns out that the floater magnet wants to align itself with the spinning magnet, but it cannot spin fast enough to do so. And for as long as this coupling is maintained it will hover or levitate,” says Rasmus Bjørk, and continues:
“You might compare it to a spinning top. It will not stand unless it is spinning but is locked into position by its rotation. It is only when the rotation loses energy that the force of gravity – or in our case the push and pull of the magnets – becomes large enough to overcome the equilibrium.”
Reference: “Magnetic levitation by rotation” by Joachim Marco Hermansen, Frederik Laust Durhuus, Cathrine Frandsen, Marco Beleggia, Christian R.H. Bahl and Rasmus Bjørk, 13 October 2023, Physical Review Applied.