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Tuning techniques for kinetic MEMS energy harvesters

The paper considers piezoelectric vibrating micro electromechanical system (MEMS) harvesters with variable effective spring stiffness. The structure of the harvesters is consists of proof mass suspended by an elastic beam. A viscous damper reflects the energy dissipation of the system. Piezoelectric layers, disposed on the maximum stress zone of the beam surface, are used as generators of electric energy. The stiffness of the beam is varied by capacitors, which are positioned at the maximum deflection zone of the beam. Different types of feedback circuits are used in order to investigate their influence on the resonant frequency of the system. Furthermore, two types of capacitors with transverse and lateral action are applied. According to the type of these capacitors and to the feedback circuits twelve different systems are considered. The dynamic models of those systems have been investigated in order to compare their tuning capability. The results, presented in the paper, could be useful for the designers of tunable kinetic MEMS harvesters.