Bidirectional actuation of ferrofluid using micropatterned planar coils assisted by bias magnetic fields

Sensors and Actuators A: Physical, Volume 173, Issue 1, January 2012, Pages 219-226
B. Assadsangabi, M.S. Mohamed Ali, K. Takahata

Department of Electrical and Computer Engineering, University of British Columbia, 2332 Main Mall, Vancouver, BC, V6T1Z4, Canada

Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia

Abstract

This paper reports a ferrofluid control method that enables both attraction and repelling of ferrofluid on micropatterned planar coils coupled with permanent magnets. A combinational use of a controlled magnetic field and a bias field is shown to provide lateral forces that attract/repel the ferrofluid to/from the coil depending on the direction of the current passed through the coil. Active mirror devices whose mirrors are switched by ferrofluids are developed as a proof-of-concept of the actuation method toward the application to imaging devices and optical switches. The planar devices lithographically fabricated to have arrays of mirror-coil cells are used to demonstrate activation/deactivation of individual cells enabled by the bidirectional radial motion of the ferrofluid layer with ∼100 um thickness. The static and dynamic behaviors of the ferrofluid in the devices are characterized through an image processing approach. Multiple mirror cells are selectively and simultaneously operated to show enhanced ferrofluid control uniquely available with the two modes of the actuation as well as to demonstrate pattern generation with the arrays.

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