Electromagnetic suspension (EMS) is the magnetic levitation of an object achieved by constantly altering the strength of a magnetic field produced by electromagnets using a feedback loop. In most cases the levitation effect is mostly due to permanent magnets as they have no power dissipation, with electromagnets only used to stabilise the effect.
According to Earnshaw's Theorem a paramagnetic body cannot rest in stable equilibrium when placed in any combination of gravitational and magnetostatic fields. In these kinds of fields, an unstable equilibrium condition exists. Although static fields cannot give stability, EMS works by continually altering the current sent to electromagnets to change the strength of the magnetic field and allows a stable levitation to occur. In EMS, a feedback loop which continuously adjusts one or more electromagnets to correct the object's motion is used to cancel the instability.
Many systems use magnetic attraction pulling upwards against gravity for these kinds of systems as this gives some inherent lateral stability, but some use a combination of magnetic attraction and magnetic repulsion to push upwards.
Magnetic levitation technology is important because it reduces energy consumption, largely reduces friction. It also avoids wear and has very low maintenance requirements. The application of magnetic levitation is most commonly known for its role in maglev trains.