  In this paper, a novel electret-based capacitive energy harvesting device has
been developed according to out-of-plane gap closing scheme. The device is
composed of a micro cantilever and a substrate which form a variable capacitor
and is in series with a resistance. An electret material is used to provide the
bias voltage which is needed in capacitive energy harvesters in order to
scavenge energy from ambient vibration. The ambient vibration is applied to the
system as a harmonic base excitation. The motion equations and the
corresponding boundary conditions are derived using Hamilton's principle based
on Euler-Bernoulli beam theory and the Kirchhoff's voltage law is employed to
couple the mechanical and electrical fields. The equations of motion are
discretized using Galerkin procedure and integrated numerically over time.
Pull-in instability of the system is investigated in both static and dynamic
cases. The effect of various parameters on the behavior of the device is
studied. The maximum theoretical harvested power is resistance in the order of
1 micro-watt.
