Multibeams energy harvester for rotational low-frequencies

The mechanical vibration induced by rotation speed is gaining interest in the last years. Comparing to other mechanical vibration sources, the excitation by rotational speed from low power wind turbines is really a challenge since the vibration frequency is lower than 10 Hz and it generates accelerations higher than 1 g. In this paper, a rotating piezoelectric energy harvester is designed and analysed. In order to achieve the best electrical power performance, the prototype is designed to have low natural frequencies varying the hub positions and dimensions of the multi-beams, decreasing the crossing-frequency (natural frequency/rotation speed) and finding the optimal electrical load resistance. The dynamic behaviour of the harvester is simulated using a nonlinear one-dimensional finite element formulation. The rotating piezoelectric beam is formulated by means of a geometrically nonlinear finite element with six mechanical degrees of freedom and one electrical degree of freedom per node. The simulations are performed from 1 to 4.5 Hz (60 - 270 rpm) rotation speeds. A performance assessment is done investigating the influence of the hub positions, crossing-frequencies, electrical resistance and rotation speeds over the voltage and power generation. Regarding harvester's performance, promising results are obtained since the output power 3.72 mW @ 3.61 Hz. In this sense, this article provides a prototype at low rotational frequency capable to scavenge energy from low power wind turbines.