Low Resonance Frequency Piezoelectric MEMS Harvester with Shear Mode

Low Resonance Frequency Piezoelectric MEMS Harvester with Shear Mode
MEMS; Piezoelectric; shear mode; spiral; energy harvesting
Issue Date
International Workshop on Piezoelectric Materials and Applications in Actuators
, 34-34
Energy harvesting from the environment has been of great interest as astandalone power source of wireless sensor nodes for Ubiquitous Sensor Networks(USN). In particular, the piezoelectric energy harvesting from ambient vibrationsources has intensively researched because it has a relatively high power densitycomparing with other energy scavenging methods.Through recent advances in low power consumption RF transmitters andsensors, it is possible to adopt a micro-power energy harvesting system realized byMEMS technology for the system-on-chip. However, the MEMS energy harvestingsystem has serious drawbacks such as a high natural frequency over 300 Hz and asmall power generation due to a small dimension.To overcome these limitations, we devised a novel power generator with aspiral spring structure. The natural frequency ofa cantilever could be decreased to theusable fi-equency region (under 300 Hz) because the natural fi-equency depends on thelength of a cantilever. The energy harvester with the spiral spring structure wasfabricated by a silicon MEMS process. The piezoelectric thick film was formed byscreen printing method and then it was also treated by Cold Iso-static Press(CIP) toimprove the properties of the thick fllm. In this study, the natural frequency of theenergy harvester was a lower than a normal cantilever structure and sufficientlycontrollable in 50 - 200 Hz frequency region as adjusting weight of proof mass.Moreover, the MEMS energy harvester had a higher energy density as using shearmode (dis) which is much larger than a 33 mode (dgg) because the energy conversionefficiency is proportional to the piezoelectric constant (d).We expect the spiral type MEMS power generator would be a good candidate as astandalone power generator for USN.
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