Rotary liquid droplet microbearing

Brian E. Yoxall, Mei Lin Chan, Ryan S. Harake, Tingrui Pan, David A. Horsley

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


A rotational stage with a 10-mm-diameter single-crystal silicon rotor supported by liquid droplet ball bearings is described. The 100-300-μm- thickness droplet bearings are retained on the rotor surface with a micropatterned amorphous-flouropolymer-based superhydrophobic (SHP) surface coating that yields a 156 ° contact angle. The droplets slide on a SHP bearing raceway that is formed from laser-roughened polydimethylsiloxane (PDMS) on the surface of the stator, achieving a 10 °-contact- angle hysteresis that results in very low sliding friction. The stage is driven by a rotating external magnetic field that provides up to 3 μN ̇ m torque through a permanent magnet mounted on the rotor. The liquid bearing provides a passive wear-free interface between rotor and stator with a measured drag coefficient of 0.94 ̇ 10 -3 μN ̇ m/r/min, rotating up to a speed of 2400 r/min, and a mean minimum operating torque of 0.3 μN ̇ m. The bearing design is stable in position and tip/tilt, with a tip mode stiffness of 5.4 μN ̇ m/deg and measured nonrepeatable rotor wobble of 0.3 mrad. The experimentally measured bearing stiffness, drag coefficient, and startup torque are shown to compare well with values predicted from analytical models based on surface tension forces on the droplet bearings.

Original languageEnglish (US)
Article number6155582
Pages (from-to)721-729
Number of pages9
JournalJournal of Microelectromechanical Systems
Issue number3
StatePublished - Feb 23 2012


  • Capillary force
  • friction
  • liquid bearings
  • microactuators
  • microelectromechanical systems (MEMS)
  • rotary stage
  • superhydrophobic (SHP)
  • surface tension

ASJC Scopus subject areas

  • Mechanical Engineering
  • Electrical and Electronic Engineering


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