Structural Optimization Of Cantilever Piezoelectric Energy Harvesting Devices

With application of low-power wireless sensors and portable electronics increasing steadily, electrochemical batteries have revealed several disadvantages such as limited life span and energy density, replacement and maintenance trouble, environmental damage, etc. The research of energy harvesting to achieve self-power supply is significant and has wide prospect. The environment is subjected to vibration commonly. There are three methods for vibration energy harvesting, namely, electromagnetic, electrostatic, and piezoelectric harvesting. Piezoelectric energy harvesting has attracted the most attention because of its simple structure, wide applicability and operation without extra power source.The two modes of piezoelectric energy harvesting are 3-1 mode and 3-3 mode. The optimizing of piezoelectric energy harvesting includes circuit optimization and structural optimization. And approaches of structural optimization cover frequency matching, strain distribution improving, electromechanical coupling coefficient enhancing, etc.This paper has proposed a novel cantilever piezoelectric energy harvester with H-shaped proof mass. The purpose of design is to achieve uniform strain distribution along the extending direction of cantilever and to improve material utilization effectively. In theory, an ideal simplified model of H-shaped mass structure was established. The modals and relationship between relevant parameters when uniform strain distribution appeared were calculated. In FEM analysis, a design of H-shaped mass structure was established. Reasonable mass ratio and vibration modals at several resonant frequencies were attained. A prototype of the H-shaped mass structure was designed, manufactured, and tested according to the result of theory calculation and FEM analysis. The strain distribution of prototype was much better than that of traditional beam. When the mass ratio of the two detached metal blocks in the H-shaped proof mass has reached a certain value, the proposed device employs uniform strain distribution along the direction of its extension to allow all infinitesimal electro-active elements to possess equal strain. This conclusion has been proven by theoretical analysis, FEM analysis and experimental results. The proposed design of H-shaped mass structure can improve material utilization effectively.