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Piezoelectric energy harvesters are suitable for vibration energy harvesting due to simple design, operation and fabrication in MEMS technology. Cantilever structures fixed from one end and seismic mass at the other must tune to different resonance frequency to ensure wideband frequency operation. Adequate width to length ratio of cantilever is required to avoid curling of cantilevers (bending). Effect of increase in width of the cantilever structure on resonance frequency has been investigated and also compared analytically in this paper. An optimized design has been proposed which compensates for the increase in resonance frequency due to increase in width by changing the geometry of the seismic mass. With the change in geometry of seismic mass a shift in center of mass has been achieved towards the free end of the cantilever which reduces the resonance frequency which is desirable. The design optimization of seismic mass reported in this paper reduces the resonance frequency by 4.27 % which is appreciated as it is required to harvest ambient vibrations having low frequency. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]