This study is mainly focusing on the effectiveness of piezoelectric energy harvesters (PEHs) under volume constraints. A bimorph piezoelectric cantilever is considered for the investigations. A model is derived in order to obtain the system parameters as functions of the geometrical and the material parameters. The influences of the geometrical parameters on the maximum power are investigated under the same input excitation and a given material. It is found that the power output is strongly dependent on the geometrical parameters (length, width, thickness and tip mass).

The importance of volume for the effectiveness of PEHs is discussed by comparing the power output and bandwidth of six PEHs of different volumes, tuned to the same resonance. The mechanical damping, electrical damping and normalized power to the volume are investigated. The optimized operating conditions of the applied load resistance and the excitation frequency are investigated. A method proposed for evaluating the effectiveness of the PEHs is presented by comparing their performance to a reference optimized PEH of the same entire volume. The performance of the array PEHs is discussed in comparison with a single reference PEH with the same entire volume as the array. The model in extended to derive the power output taking into account the electrical interactions between the elements. Guidelines are presented for designing the array PEHs.

The self-resonating behavior of a freely-sliding mass along a clampedclamped beam is applied to piezoelectric energy harvesting. The effectiveness of the self-resonating PEH is investigated by comparing it to the optimized reference PEH of the same entire volume. The volume is found to be a significant criterion for the effectiveness of PEHs. It is necessary to optimize the developed PEHs under volume constraints in order to be more effective.