  In this study, we propose a design methodology for a piezoelectric
energy-harvesting device optimized for maximal power generation at a designated
frequency using topology optimization. The proposed methodology is adapted to
the design of a unimorph-type piezoelectric energy harvester, wherein a
piezoelectric film is affixed to a singular side of a silicon cantilever beam.
Both the substrate and the piezoelectric film components undergo concurrent
optimization. Constraints are imposed to ensure that the resultant design is
amenable to microfabrication, with specific emphasis on the etchability of
piezoelectric energy harvesters. Several numerical examples are provided to
validate the efficacy of the proposed method. The results show that the
proposed method yields optimized substrate and piezoelectric designs with an
enhanced electromechanical coupling coefficient, while allowing the
eigenfrequency of the device and the minimum output voltage to be set to the
desired values. Furthermore, the proposed method can provide solutions that
satisfy the cross-sectional shape, substrate-dependent, and minimum output
voltage constraints. The solutions obtained by the proposed method are
manufacturable in the field of microfabrication.
