Liquid carrying capacity: From liquid bridge bearing to ferrofluid bearing

Inspired by liquid bridge bearings, a kind of ferrofluid (FF) bearing is proposed in this work. The bearing contains two plates with a drop of FF sandwiched between them. To restrain and position the FF, a cylindrical magnet is implanted in the lower plate. The carrying capacity of the liquid bridge and FF bearing is tested and compared. The results indicate that both bearings can provide a certain amount of liquid supporting force. For similar geometries, the maximum force generated by the FF bearing (1.60 N) is about 20 times higher than that of the liquid bearing (0.08 N). Moreover, due to the effect of the magnetic field, the supporting performance of the FF bearing is more stable, especially in small gap heights. To further understand the supporting mechanism, a model of the FF bearing for the carrying capacity was built and validated by the experiment. Theoretical analysis manifests that, compared with the Laplace force, the magnetic force acts as a dominant contribution to the FF bearing. This work provides an interesting way to create liquid support for MEMS applications that demand controllable micro-platforms or frictionless bearings.