丁香园AV

Synopsis

While magnetic levitation of type I and type II superconductors had been achieved as early as in 1947 (Arkadiev) and in 1989 (Brandt), diamagnetic levitation was only demonstrated quite recently when Geim et. al. (1997) successfully floated a variety of small objects (frogs, grasshoppers, water-drops, flowers ... ) in a 16T magnetic field inside a coil. Although it is always fascinating to see objects floating without any suspension, these experiments were very surprising to the physics-archive community because of Earnshaw's theorem (1842) which forbids the levitation of a magnet by another magnet.

In this talk, we will discuss why the diamagnetic levitation is permissible, what are the essential conditions for the stable levitation. Furthermore, we will learn an optimization algorithm to arrange magnetic sources (some current carrying coils) to maximize the levitating force. This algorithm may be interesting to inspire magnet designs.