Dynamic characterization of fabricated guided two beam and four beam cantilever type MEMS based piezoelectric energy harvester having pyramidal shape seismic mass

Piezoelectric energy harvesters are gaining importance due to simplicity in design, operation and ability to power microelectronic sensor nodes in remote areas. A cantilever based piezoelectric energy harvester acts as a spring mass damper system having a resonance frequency tuned with ambient vibrations of low frequency. Maximum potential is generated when the resonance frequency of the energy harvester matches with frequency of ambient vibration. The highlight of this paper is a pyramidal shape seismic mass which results in a higher generated potential as compared to the square shaped seismic mass. This pyramidal shape is realized using tetra methyl ammonium hydroxide CMOS compatible 25 wt% wet etching. Two beam and four beam structures are front released using deep reactive ion etching which are fixed from both ends and having pyramidal shape seismic mass at the center. This paper presents a comparison of guided four beam and two beam cantilever type piezoelectric energy harvester fabricated using MEMS technology using a laser doppler vibrometer (LDV). Experimentally using LDV the resonance frequency for the fabricated guided two beam cantilever structure resonance frequency is 1971.9 Hz and for the guided four beam cantilever structure is 2540.6 Hz. Bandwidth for two beam cantilever structure is 40.6 Hz whereas for four beam cantilever structure bandwidth comes as 101.9 Hz. The maximum displacement measured for two beam cantilever structure at resonance frequency is 49.67 nm and for four beam cantilever structure maximum displacement is 32.17 nm. FEM (Finite Element Method) analysis for the guided two beam and guided four beam device is also performed and parameters such as resonance frequency, displacement, electric potential and von Mises stress are also reported and compared in this paper. Further the resonance frequency calculated analytically and the results obtained from FEM simulator and experimental results are also compared and it is found that they are in close agreement with each other.