Tuning Techniques for Piezoelectric and Electromagnetic Vibration Energy Harvesters

This paper is focused on resonant vibration energy harvesters (RVEHs). In applications involving RVEHs the maximization of the extraction of power is of fundamental importance and a very crucial aspect of such a task is represented by the optimization of the mechanical resonance frequency. Mechanical tuning techniques (MTTs) are those techniques allowing the regulation of the value of RVEHs mechanical resonance frequency in order to make it coincident with the vibration frequency. A very great number of MTTs has been proposed in the literature and this paper is aimed at reviewing, classifying and comparing the main of them. In particular, some important classification criteria and indicators are defined and are used to put in evidence the differences existing among the various MTTs and to allow the reader an easy comparison of their performance. Finally, the open issues concerning MTTs for RVEHs are identified and discussed.