Figure 1 shows a schematic of the micro electret generator
proposed in the present study. When vibration in the in-plane
direction is applied, the seismic mass with electret undergoes
a relative motion with respect to the counter electrode on the
bottom substrate. Thus, the amount of the induced charge on
the counter electrode is changed due to the change in the overlapping
area, producing electric current in the external circuit.
The seismic mass is supported by parylene high-aspect-ratio
springs [7], which enable large amplitude oscillation and low
resonance frequency.
Figure 2 shows a simplified model of the generator, where
σ, d, and g are respectively surface charge density, thickness
of the electret film, and gap between the electret and the counter
electrode. The length x1 represents the overlapping area be-