The paper presents numerical and experimental investigations on a bi-directional multi-modal energy harvester which is based on a piezoelectric saw-tooth cantilever array. The harvester is composed of four piezoelectric cantilevers which are connected rigidly to each other. At each junction of the cantilevers, there are placed seismic masses which are used to reduce resonant frequencies of the cantilever array. Moreover, at the center of the cantilever array is placed a Z-shaped seismic mass, which is used to obtain an additional rotation moment during excitation of the energy harvester to this way increase the stability of output characteristics via the whole angular range. The rigid connection between cantilevers ensures the transfer of bending deformations from cantilevers which are resonant to cantilevers which are out of resonance operation mode. The design of cantilever array ensures that all piezo ceramics are affected or partly affected by bending deformations while excitation frequency changes from 10 Hz to 160 Hz. In addition, such a composition of the array ensures the multi-modal operation principle. Additionally, the proposed cantilever array is designed to respond to changes of excitation force angle in an XY plane. The numerical and experimental investigation have shown that the proposed energy harvester has four resonant frequencies at a range from 10 Hz to 160 Hz. The electrical characteristics of the harvester were investigated as well. The results of these investigations have shown that cantilever array is able to provide an average output power of 15.3 mW while excitation amplitude is 0.5 m/s2 and the angle of excitation force changes in range from 0° to 350°.
Keywords: bi-directional energy harvester; cantilever array; multi-modal piezoelectric energy harvester; piezoelectric energy harvester.