Rotational energy harvesting has received massive attractions due to the abundance and availability of rotational motions in ambient environments. This paper considers a rotational impact energy harvester by utilizing the static instability of a centrifugal softening beam. During the rotation, two rigid piezoelectric beams are impacted by the centrifugal softening driving beam to generate electric energy. When the rotational frequency is increased, with the centrifugal effect, the amplified relative motion between the driving and generating beams significantly contributes to the increase of the impact force and in turn the output power. The theoretical model is developed and used for numerical simulation. It is shown that the output voltage can be significantly improved with the centrifugal softening effect. Furthermore, the impact force is demonstrated to prevent the driving beam from continuously deflecting and suffering the mechanical failure.
This paper aims to improve the off-resonance energy harvesting performance of a vibration-based energy harvesting system by exploiting the dynamic interaction between two attractive magnets. A static force-displacement model is firstly derived by a simple experiment to describe the magnetic force and then extended to the dynamic model to characterize the transient interaction of the magnets. A theoretical model is developed and experimentally verified to be capable of accurately predicting the voltage and power outputs of the proposed off-resonance energy harvesting system with different resistive loads. The performance of the proposed energy harvesting system under off-resonance excitations is examined and evaluated by comparing with the one of the system without magnetic interaction. Results reveal that the nonlinear dynamic force induced by the relative motion between the two magnets could significantly enhance the off-resonance power output. The influence of the distance between the two magnets, as well as the external resistive load, on the voltage and off-resonance power outputs of the system is studied. The proposed magnetic field enhanced energy harvesting system has 1760 times more power output than the counterpart system without magnetic interaction at the off-resonance harmonic excitation of 3 Hz and 0.5 m/s2 and an optimal resistance of 20 kΩ.
Recently, vibration energy harvesting from surrounding environments to power wearable devices and wireless sensors in structure health monitoring has received considerable interest. Piezoelectric conversion mechanism has been employed to develop many successful energy harvesting devices due to its simple structure, long life span, high harvesting efficiency and so on. However, there are many difficulties of microscale cantilever configurations in energy harvesting from low frequency ambient. In order to improve the adaptability of energy harvesting from ambient vibrations, a two degrees of freedom (2-DOF) magnetic-coupled piezoelectric energy harvester is proposed in this paper. The electromechanical governing models of the cantilever and clamped hybrid energy harvester are derived to describe the dynamic characteristics for 2-DOF magnetic-coupled piezoelectric vibration energy harvester. Numerical simulations based on Matlab and ANSYS software show that the proposed magnetically coupled energy harvester can enhance the effective operating frequency bandwidth and increase the energy density. The experimental voltage responses of 2-DOF harvester under different structure parameters are acquired to demonstrate the effectiveness of the lumped parameter model for low frequency excitations. Moreover, the proposed energy harvester can enhance the energy harvesting performance over a wider bandwidth of low frequencies and has a great potential for broadband vibration energy harvesting.
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