Research On The Dynamic Characteristics Of A Direction Self-adaptive Piezoelectric Energy Harvester

Wireless sensor network technology is a revolution in the field of information sensing and harvesting,which has brought profound impact on human beings in all aspects of social production and life.For a long time,the energy supply of wireless sensor network systems mainly depends on chemical batteries,which have low energy density and are easy to pollute the environment.Therefore,the pursuit of sustainable clean energy supply has become the goal of many scholars.In order to effectively utilize the widely distributed vibration energy in the wireless sensor network work site,researchers have proposed a variety of vibration energy harvesting schemes based on the piezoelectric effect,but the conventional piezoelectric energy harvesting scheme can only effectively harvest vibration energy in a single direction.Although researchers have proposed some deformed structures for cantilever beams to adapt to vibration energy in different directions,most current research schemes have low power density and require the integration of multiple power management circuits.There are also issues such as the inability to automatically adjust and follow with changes in excitation direction,and the harvesting efficiency needs to be improved.Since the direction of environmental vibration is not unique,how to achieve stable and consistent high level output in all directions without adding power management circuit is the key research goal of multi-directional energy harvesting.Therefore,it is very necessary to carry out research on adaptive energy harvesting that can automatically follow the excitation direction.In addition,there is no complete performance evaluation method in the existing multi-directional energy harvesting scheme,and there is no relevant research scheme in the existing literature on how to harvest the vibration energy of multiple degrees of freedom in the single-mass stiffness model at the same time.With the support of the general program of the National Natural Science Foundation of China,this paper takes the multi-degree of freedom single cantilever beam structure as the research object,and conducts in-depth research on the basic theory of direction self-adaptive energy harvesting,the performance evaluation method of multi-directional energy harvesting,and the efficient hybrid energy harvesting scheme,which provides scientific and effective support for the design of multi-directional piezoelectric energy harvester.The main research contents of this paper are as follows:(1)Research on direction self-adaptive mechanism of piezoelectric energy harvesting.Aiming at the disadvantage that the existing multi-directional energy harvesting scheme cannot automatically follow the direction of external excitation,the concept of "direction self-adaptive energy harvesting" is proposed and a basic theoretical model of self-adaptive energy harvesting based on multi-degree-of-freedom single cantilever beam structure is constructed.The dynamic equation of the energy harvesting system is established by using the second Lagrange equation,and the analytical solution of the steady-state vibration process of the system is obtained by using the multi-scale method.The vibration process of the energy harvesting system is described in detail.The prototype is manufactured and the experiment verifies the effectiveness of energy harvesting in the self-adaptive process and steady-state vibration process of the system.Further,with the aim of improving the energy harvesting efficiency,the influence of the key parameters of the system on the energy harvesting efficiency is studied,and the harvesting efficiency of the direction self-adaptive energy harvester and the existing multi-directional energy harvesting scheme is compared.(2)Research on performance evaluation method of multi-directional energy harvesting.Eulerian angles are used to define the complex excitation in any direction in the three-dimensional space,and the distributed parameter model of the energy harvesting system is established according to the moment balance and force balance equations of the micro-element.The change law of the natural frequency and the rotational resistance moment of the cantilever beam when the external excitation direction changes is studied,as well as the dynamic response of the self-adaptive energy harvester under different excitation directions.The concept of "energy harvesting workspace" is proposed and the performance evaluation method of multi-directional energy harvesting is established.The workspace is expressed by the external excitation angle and output voltage amplitude,and the performance of the energy harvester is evaluated by the volume wrapping method and the area covering method.The key factors limiting the direction self-adaptive energy harvesting workspace are obtained.(3)Study on energy transfer mechanism between multiple degrees of freedom of direction self-adaptive energy harvester.The damping,excitation,nonlinearity and coupling parameters in the dynamic equation are readjusted and the detuning parameters are introduced.The analytical equation is derived by using the multi-scale method when the frequency ratio of the vibration and rotational degrees of freedom is 2:1,and three stable solutions of the autonomous system are obtained.Through the numerical iterative calculation of the analytical equation,the energy saturation phenomenon and amplitude jump phenomenon between the two degrees of freedom under different detuning parameters,as well as the improvement effect of the two nonlinear peaks on the rotational degrees of freedom on the energy harvesting broadband performance are described.Furthermore,the influence of excitation amplitude,electromechanical coupling coefficient,time domain constant and other parameters on the resonance frequency and amplitude response of the energy harvesting system is studied.(4)Research on output characteristics of direction self-adaptive hybrid energy harvester.On the basis of direction self-adaptive energy harvesting,a structural design scheme of hybrid energy harvesting is proposed to harvest the vibration energy of the cantilever beam in the rotational degree of freedom.The working principle and realization method of continuous rotation on the rotational freedom of cantilever beam are experimentally studied;Based on the theory of magnetic dipole,the magnetic model in three-dimensional direction is deduced,and the role of magnetic coupling effect in hybrid energy acquisition is discussed;A prototype is designed and manufactured,and the output characteristics of the hybrid energy harvesting system in vibration and rotation degrees of freedom are experimentally studied.The effective working range of the electromagnetic energy harvesting module and the relationship between the output voltage and the magnet spacing are also studied.The research in this paper provides a new idea for multi-directional energy harvesting,and realizes the multi-directional,self-adaptive,hybrid energy harvesting and other functions of a single cantilever beam.This is the first exploration of the new functions of the cantilever beam structure.In the field of piezoelectric energy harvesting,cantilever beam is widely used in various linear and nonlinear energy harvesting devices.The research results of this paper are expected to be applied in most scenarios of current cantilever beam applications,and provide a potential energy supply scheme for wireless sensors.