In particular, the interaction between
electronics and mechanics can be accurately
studied: the deflection of the upper plate
initiates a positive feedback effect, since it
reduces the air gap. This increases the electrostatic
field between the plates and the
force, which causes the deflection to become
even stronger. A second effect is due to the
capacitance between the two plates. The capacitance
is calculated dynamically by an
integration over the bending line. Capacitance
rises when the plate is deflected. It is
parallel to the "storage" capacitance, and has
an influence on the electronic circuit, but its
effect is minor since it is two orders of
magnitude below the storage capacitance.
This effect is far more interesting in the
examination of capacitive pressure sensors.
The goal of the first simulation is to
extract the shape of the bending line. In Fig.
4, it is compared with the results of the
finite-element simulator ANSYS1" 181. The
discretization was set to 36 nodes for both
simulations. In both cases, the electromechanical
positive feedback effect was taken
into account. The shape of the bending line
is nearly identical. The displacement difference
is about 6 percent, and is due to the
different underlying approaches- finite
differences vs. finite elements-which pro-