結合轉軸之分段非線性拉伸式壓電能量採集器之設計與分析

Abstract

傳統的壓電懸臂樑採集器有幾個明顯的缺點，如採集頻寬窄、應變分布不均等，使採集器的發電效率低落。為了改善上述情形，本研究提出一種結合旋轉接頭之分段非線性能量採集器，透過幾何結構產生非線性效果，進而拓展系統的頻寬，並施予壓電材料軸向預力使其在振動過程中產生均勻的軸向應變，且結構所帶來的力放大效果除了影響系統的共振頻外，也進一步提高了採集器的輸出電壓。本研究將特殊設計的剛體塊視作主體，一端為旋轉接頭，另一端則透過簡支邊界與PVDF壓電材料接觸，在此將PVDF壓電材料視作彈性桿件，兩端以夾持方式固定，又因其剛性遠小於剛體塊，故在理論模型中忽略其彎矩剛性與質量。此外，本研究也針對採集器的各項參數進行實驗，包括等效剛性、預拉力值、激振加速度、簡支邊界質量、簡支邊界位置等，探討各參數對於系統性能的影響，並將實驗結果與理論模型進行驗證，最後與傳統懸臂樑能量採集器做比較。實驗結果顯示，本研究所設計之採集器與懸臂樑採集器相比，最大方均根電壓提高了3倍，且頻寬也提升了13倍，在3.33 MΩ的外接阻抗下，最大輸出功率可達0.47 mW。

The traditional cantilever piezoelectric energy harvester has some disadvantages such as narrow bandwidth and uneven strain distribution, which leads to low power generation efficiency. To address these issues, this study proposes a piecewise nonlinear piezoelectric energy harvester composed of a specially designed rigid body and an elastic PVDF sheet. Due to the force-amplification mechanism, the PVDF subjected to axial preload is stretched uniformly to influence the system’s resonant frequency and increase the output voltage. The dynamic equations of the proposed energy harvester is derived based on the motion of the rigid body which is considered as the only degree of freedom. In the theoretical model, the mass and the bending stiffness of the piezoelectric sheet are ignored because the stiffness of the piezoelectric sheet is much smaller than that of the rigid body. Experimental results are conducted to verify the theoretical model. The influence of stiffness, preload, acceleration, and mass configuration will be discussed in the verification. The experimental results show that the output voltage of the proposed design is increased by 2.52 times and the bandwidth is extended by 13 times compared with the traditional cantilever energy harvester. According to the optimal resistance experiment results, the maximum output power can reach 0.47 mW with an optimal resistance of 3.33 MΩ.