Page 252 - Mechanics of Microelectromechanical Systems

4. Microtransduction: actuation and sensing 239
shrinking of the top layer generates a strain the bottom fibers of the top
layer are prevented from fully shrinking by the adjacent bottom passive layer.
As a consequence, there is a distribution in the axial deformation, from a
maximum shrinking in the free top fiber to a minimum shrinking registered
in the bottom (interface) fiber of the active layer. The same deformation
trend is followed by the bottom (passive) layer due to its attachment to the
top layer.

Figure 4.51 Bending deformation of a bimorph with shrinking top active layer: (a) general
configuration; (b) Detail of deformed sandwich

Figure 4.51 (b) also indicates the forces and moments that are acting on
each of the two layers, as produced by the induced free strain If one
analyzes the interface fiber belonging to the active layer, there are three types
of strains that linearly superimpose under the assumption of small
deformations, namely: the free strain an axial strain generated by the
action of the force and another strain component resulting from the
bending of this layer. The same interface fiber also belongs to the bottom