Daily Archives: May 20, 2024

What is Magnetic Levitation?

Many systems such as flywheels, Maglev trains, and other high-speed machinery already use magnetic levitation. The Brookhaven National Laboratory had pioneered this technology in the late 1960s. Maglev trains use the magnetic levitation technology, where superconducting magnets keep a train car suspended above a U-shaped concrete guide-way. Like regular magnets, superconducting magnets repel one another when like poles face each other. Systematically electrifying propulsion loops in the system creates moving magnetic fields that pull the train car forward from the front and push it forward from the rear. As the train car is floating in a sea of interacting magnetic fields while moving, the trip is very smooth and very fast, reaching up to 375 miles per hour (ca. 604 km/h).

Now, at the Technical University of Denmark, latest research has given this old technology a new twist. They have shown it is possible to levitate a magnet simply by rotating another similar sized magnet near it. Hamdi Ucar, an electronics and software engineer, had first demonstrated this unusual effect in 2021. The team at TU Denmark is using this effect to exploit contactless object handling or for trapping and manipulating microplastics made of ferromagnetic materials.

Magnetic levitation can be of three types. The first of these is active magnetic stabilization. Here, a control system supplies the magnetic force that keeps the levitating object under balanced conditions. The second type is used by Maglev trains and is known as electrodynamic suspension. In this case, a moving magnet induces a current in a stationary conductor, which then produces a repulsive magnetic force. This force increases with the speed of the moving magnet. The third type is the spin-stabilized levitation. Here, a levitating magnet spins at about 500 RPM or revolutions per minute. Gyroscopic effect keeps the magnet stable.

The TU-Denmark type of levitation is a variation of the third type. It involves two magnets—a rotor, and a floater. The rotor magnet is mounted on a motor. It has its magnetic poles oriented perpendicular to its rotational axis. The motor makes it rotate at velocities of about 10,000 RPM. The TU-Denmark team used a spherical magnet, made from neodymium-iron-boron, and 19 mm in diameter.

The floater magnet, placed under the rotor, begins to automatically spin with the spinning rotor, moving upwards towards the rotor to hover in space a few centimeters below it. The frequency of precession of the floater is the same as that of the rotor and has its magnetization oriented near to the rotation axis, matching that of the like pole of the rotor. When disturbed, the interacting magnetic fields forces it back to its equilibrium position.

The team used computer simulations, taking into account the magneto-static interactions between the two magnets. They found the new type of levitation is caused by a combination of magnetic dipole to dipole coupling, and the gyroscopic effect. They explained it as a magneto-static force of one magnet exerting an attractive and repulsive force on the other.

Furthermore, they explained that the process goes on to create a midair energy minimum in the potential of interaction between the dipoles. The team’s computer modelling revealed this minimum, where the floater could stably levitate.