Indirect impact based piezoelectric energy harvester for low frequency vibration

This paper presents an impact based piezoelectric vibration energy harvester using freely movable metal spheres as proof mass and an MFC (Macro Fiber Composite) beam as a piezoelectric cantilever. External vibration is transformed into free motion of metal spheres inside the channels and impact between the metal sphere and channel end induces a vibration of the MFC beam to generate electric power. A proof-of-concept device having the form-factor of a conventional wristwatch has been designed and tested to harvest energy from low frequency human-body-induced vibrations. Geometry at both ends of the cavities has been optimized to effectively transmit energy to piezoelectric cantilever and thus achieve a higher output power. For a device having an effective volume of 4.59cm³, maximum peak-to-peak open circuit voltage of 54V and RMS output power of 621μW have been achieved, when the fabricated energy harvester was mounted on a wristwatch and shaken manually.