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Paper focuses on investigation of the piezoelectric energy harvester which operates at multi – frequency mode. Employment of such operating principle extends frequency response spectrum and ensures higher efficiency of the harvester. Multi – frequency energy harvester has saw-tooth shape and consists of four piezoelectric cantilevers which are connected rigidly to each other by specific angle (Fig.1). Four seismic masses are attached to each junction in order to make resonant frequencies of each cantilever lower and to increase strain of the piezo ceramic layer. The aim of the proposed harvester design is to employ vibrations of the harvester with dominated first and second bending modes of the cantilevers for electric energy generation. Such design allows to excite partial bending modes of the cantilevers at low excitation frequency and special vibration modes of the harvester at the higher excitation frequency spectrum. Therefore harvester can operate at wide frequency response spectrum.
Numerical investigation using finite element modeling software COMSOL 5.2 was performed. Characteristics of the materials, geometrical parameters of the cantilevers and boundary condition were investigated. Firstly, modal analysis was fulfilled and it revealed that energy harvester has several bending modes at the frequency range from 20 to 1200Hz. Wide distribution of the natural frequencies showed that geometrical parameters of the energy harvester should be optimized. Optimization was performed by employing parametric investigation of several parameters such as length of the cantilevers, weigh of the seismic masses and angles between cantilevers. Results of the parametric investigation revealed that resonant frequencies could be adjusted close to each other. It shows that saw tooth harvester, after structural optimization, can effectively operate ant wide excitation frequency spectrum. Prototype of the harvester was made and experimental study was performed to validate results of numerical modeling.