A novel passive mechanism to improve power output in 2DOF piezoelectric vibration energy harvester

Abstract

Cantilevered piezoelectric vibration energy harvesters are usually operated in the first mode and analysed as single degree of freedom (SDOF) systems. To improve their performance, a two degree of freedom (2DOF) system with a novel dynamic magnifier is developed by combining four bar mechanism and helical spring to act as elastic magnifier. This dynamic magnifier is attached between the base (excitation location) and the fixed end of cantilevered elastic harvester beam. To identify a suitable configuration for the dynamic magnifier, simulations are performed with two different configurations of passive mechanism, viz., 1:2 and 1:1 magnification four bar mechanisms. The natural frequencies of the first two modes obtained with 1:1 magnification four bar mechanism are close, giving good bandwidth and the mechanism is fabricated according to the simulation results. The simulated relative displacements and first two modal frequencies are in good agreement with experiments. There after macro fiber composite (MFC) with copper as substructure is used to fabricate the harvester beam within the required operating frequency range. The improvement in measured output power from 2DOF harvester over SDOF harvester is found to be 110% in the first mode and 270% in the second mode. Further, bandwidth analysis and effect of increase in magnifier mass is also investigated and performance characteristics of proposed 2DOF harvester are compared with the earlier similar harvesters. This kind of harvester with a novel four bar mechanism as a dynamic magnifier has not been reported in literature.