Research On Broadband Piezoelectric Power Harvesting Of A Bi-stable Structure

The rapid development of integrated circuit technology has promoted the wide application of micro-electromechanical systems(MEMS)in both fields of civil industry and national defense industry.As a result,the technology of vibration energy harvester using piezoelectric materials to convert mechanical vibration into electric energy has got much attention.However,the harvesters often adopt linear structure as their configuration,which limits their resonance zone at a high frequency with a narrow bandwidth.Therefore,researchers have been committed to optimizing the structure to broaden the working bandwidth of harvesters.In this paper,the development of vibration harvester is reviewed,in which the principle of the nonlinear bistable structures is examined carefully.Then,a single degree of freedom bistable harvester is established,and its energy harvesting performance is simulated and verified.Thereafter,a two degree of freedom bistable structure is proposed and its good advantages over the single degree of freedom structure in reducing the threshold and broadening the working bandwidth of the system are analyzed.The main work of this article is as follows:Firstly,a single degree of freedom bistable piezoelectric vibration energy harvester is designed and its lumped parameter model of the system is established.Taking the piezoelectric power as coupling factor,Newton's second law is used to establish the motion control equation of the system.Secondly,the equation is simulated with the four order Runge Kutta method,and the output curve of the system is obtained.Results show the working bandwidth of the bistable structure is 12 Hz,7Hz wider than that of the linear system.Then,the variable parameter analysis of the bistable structure is carried out,and results demonstrate the output of the system is mainly influenced by the initial velocity and position of the mass and the magnet spacing d.Thirdly,a two degree of freedom bistable piezoelectric harvesting structure is built and simulated.The output curve of two degree of freedom structure is compared with that of single degree of freedom structure,and results show the two degree of freedom structure can effectively reduce the threshold of the system and broaden working bandwidth,and the overall collection bandwidth is widened about 10 Hz.Fourthly,the experimental devices of the single degree of freedom structure and the double degree of freedom structure is designed respectively.The output curves of two systems are obtained by sweeping frequency.Through comparing the experimental curves with the simulation curves,it is found that the experimental results are basically consistent with the simulation results,which can verify the output curves obtained by simulation,and also verify the assumptions related to the influence of relevant parameter variation.In this paper,the broadband characteristics of single degree of freedom bistable harvester is testified after the comparison with linear structure,and the good advantages of the two degree of freedom bistable system over the single degree of freedom bistable system in reducing the system threshold and improving the overall output energy are analysied.