Theoretical And Experimental Studies On Nonlinear Piezoelectric Energy Harvesting For Broadband Rotating Motions

How to power wireless sensing nodes is one of technical difficulties of embedded sensing for rotating components. While rotating vibration energy harvesting utilizing piezoelectric effect will be effective and promising. In practice, however, operation frequencies of rotating components may be time-dependent and over a wide frequency range, instead of fixed frequencies. Thus it is not good for linear energy harvesting methods. Nowadays, how to introduce nonlinear mechanisms to enhance broadband rotating piezoelectric energy harvesting is becoming one research hot-spot.Loads acting on one rotating piezoelectric vibrator under rotating motions are much more complex than those under straight- line motions. Hence, it is a key problem that how to control and utilize nonlinearoty, and optimize the geometries of the nonlinear piezoelectric vibrator. By now, few theoretical studies have been conducted on characteristics of nonlinear rotating piezoelectric energy harvesters. Basic mechanism of utilizing nonlinearity to enhance nonlinear rotating piezoelectric energy harvesting has also not been exposed. Supported by the Natio nal Nature Science Foundation of China(Grant No.51275520), in this paper nonlinear piezoelectric energy harvesting for broadband rotating motions is studied theoretically by introducing nonlinear magnetic forces and chaotic dynamic theory. In particular, the mechanism and quantitative condition of enhancing the performanc using nonlinearity are exposed. The proposed work is of great significance to provide theoretical guidelines for engineering applications. The main contents and conclusions are summarized as follows:1、By introducing both nonlinear magnetic forces and piezoelectric coupling effect, a mathematical model of one nonlinear p iezoelectric vibrator under rotating motion is derived based on the Lagrange’s equation and the assumed- mode method. This model will provide a basis for further theoretical research.2、Two kinds of numerical algorithms are studied and compared based on finite difference method and Runge-Kutta method, respectively. Then one algorithm is used to analyze the effects of different parameters on the performance of the nonlinear rotating energy harvester. The results demonstrate that the distance between two magnets is a key parameter. When an optimal distance is achieved, the bandwidth of the nonlinear rotating energy harvester can be enlarged. Also a qualitative explanation is given.3、The Melnikov function of the nonlinear rotating energy harvester is derived based on the Melnikov method. The analytical results demonstrate that a double-well potential function is an important foundation for harvesting broadband rotating motions. Then a quantitative necessary condition is presented.4、Nonlinear force between two magnets are fitted by Finite Element Modeling. Then a parametric finite element model of the nonlinear rotating energy harvester is built. Based on it, the effects of different parameters on the output characteristics are simulated.5、An experimental system of nonlinear piezoelectric energy harves ting for broadband rotating motions is designed and built. Then the characteristics of a nonlinear rotating energy harvester and its capacity are validated by experimental testings. The results show that appropriate nonlinear magnetic force can be used to improve the performance and enlarge the bandwidth of a nonlinear rotating energy harvester. The experimental results also agree with theoretical and simulation conclusions. In addition, it can be seen that the output power of the nonlinear energy harvester is enough for a low power consumption sensor. Thus it is feasible for practical applications.