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4. Microtransduction: actuation and sensing 207
3.3.2.1 Actuation
Application of an external electric field in a pair of fixed-mobile plates
that can sustain relative rotary motion through adequate boundary conditions
will generate tangential forces which will rotate the mobile part. Figure 4.29
shows a pair of conjugate digits that are disposed at a radius with respect
to a rotation center.
Figure 4.28 In-plane rotary transduction
Figure 4.29 Geometry of a fixed-mobile digit pair for in-plane rotary transduction
The initial overlapping area between the fixed and the mobile digits is
defined by an angle as sketched in the Fig. 4.29. The radius defining
the corresponding gap suggests that several pairs can be placed
concentrically at different radii. The two curvilinear digits will have a
relative rotary motion defined by a variable angle and the capacitance
pertaining to this angular motion is:
