| The vibration energy harvesting technique is a promising solution for powering microelectronic devices such as wireless sensors with low energy consumption.Up to now,a technique for converting vibration energy to electrical energy includes electrostatic,electromagnetic,triboelectric and piezoelectric approaches.The piezoelectric vibration energy harvesting technique has attracted much attention due to its high energy density and easy integration characteristic.A typical piezoelectric energy harvester(PEH)is a linear piezoelectric cantilever beam.This typical linear harvester can operate effectively at its linear resonance frequency.However,once the ambient vibration is varied,electrical power output of this linear structure is drastically reduce.Therefore,since ambient vibrations are usually in wideband frequency or low frequency,researchers turn their interest to expanding operation bandwidth of the harvester.Aiming to achieve the high-performance piezoelectric energy harvester under broadband vibrations,an outer-inner magnetic two-degree-of-freedom piezoelectric energy harvester is proposed in this paper.Based on the linear two-degree-of-freedom harvester,a nonlinear two-degree-of-freedom harvester has been developed by introducing two opposite magnets.The proposed harvester incorporates another two opposite magnets into the original nonlinear two-degree-of-freedom system,aiming to further broaden its operating bandwidth.Based on Euler-Bernoulli beam theory,magnetization current theory,piezoelectric constitutive equation and Kirchhoff ’s law,a lumped parameter model of 2-DOF system is established,and numerical simulation analysis and experimental verification are carried out by MATLAB software to reveal the dynamic response characteristics of outer-inner magnetic 2-DOF energy harvester.Compared with the original nonlinear two-degree-offreedom system,numerical and experimental results demonstrate that the proposed harvester can offer a significantly wider operating bandwidth in a lower frequency range.In the optimal configuration(D = 14 mm,d = 10 mm),the harvester can offer an operation bandwidth of 12.8 Hz(5～17.8 Hz)under 0.3 g excitation,generating a power of 133 μW.The operating bandwidth and the harvested power are increased by 106.5% and 42%,respectively(under the same excitation of 0.3 g).In addition,the new introducing magnet force can help the inner beam easily pass through the potential well barriers under lower excitation than the original nonlinear twodegree-of-freedom system.Compared with the original technique,the excitation level acquired for high-energy inter-well oscillation of the optimal configuration is decreased by34.8%(from 0.23 g to 0.15 g).Furthermore,the proposed harvester is able to efficiently harvest energy from broadband vibration under different excitation levels because of the hardening behavior or bistable behavior with different magnet distances. |
