Solved: How a spinning magnet causes other magnets to levitate

Experimental results from DTU scientists confirm the physics behind a recently discovered phenomenon of magnet levitation.

VIDEO: Magnetic levitation starting demonstration using a 12.7 mm diameter spherical magnet and a 19 mm diameter rotating at 180 Hz. Credit: DTU.
VIDEO: Magnetisk levitation demonstreret ved hjælp af et Dremel-værktøj, der drejer en magnet ved 266 Hz. Rotormagneten er 7x7x7 mm3 og flydermagneten er 6x6x6 mm3.
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.

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 that, 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.”

VIDEO: Magnetisk levitation demonstrerede at rotere en magnet ved 180 Hz. Rotormagneten er en 19 mm diameter magnet og flydermagneten er 12,7 mm i diameter.
Magnetic levitation demonstrated spinning a magnet at 180 Hz. The rotor magnet is a 19 mm diameter magnet and the floater magnet is 12.7 mm diameter magnet. 


Rasmus Bjørk

Rasmus Bjørk Professor Department of Energy Conversion and Storage Phone: +45 46775895