Size segregation in vibrated granular systems: A reversible process

The interior of a vibrated bed of mixed-size particles is examined experimentally, revealing segregation patterns that are considerably different than the ''layered cake'' structures published in previous literature. The frequency of vibration has a strong effect on such patterns, which are destroyed when the vibration frequency is increased past approximate to 20 Hz. The segregation process is reversible; the granular system can be driven back and forth between segregated and homogeneous states by decreasing or increasing the vibration frequency.