Novel Multi-directional Functional Gradient Material Piezoelectric Energy Harvester

There are many forms of energy in the natural environment,such as solar energy,wind energy,thermal energy,vibration energy,etc.As a common form of energy in daily production and life,mechanical vibration has higher energy harvesting efficiency and lower requirements for the external environment.Therefore,compared with solar energy,temperature difference energy and other environmental energy sources,vibration energy has significant advantages in usage time,manufacturing cost,usage scenarios and energy density.Therefore,it has a very broad development prospect to power a low-power wireless sensor network by harvesting vibration energy.Most of the commonly used energy harvesters today are based on piezoelectric vibration energy harvesters,in which a piezoelectric sheet is attached to an exciter to obtain electrical energy from the ambient vibration,and the maximum energy harvesting efficiency is obtained when the resonant frequency of the system matches the ambient excitation.However,most of the existing research results focus on energy harvesters with linear resonant structures,and one of the significant problems is that the effective operating frequency range is very narrow,which leads to a slight change in the frequency of the ambient vibration and the energy harvesting efficiency will be drastically reduced.Although many researchers have proposed energy harvesters based on nonlinear vibrations in subsequent studies,they are generally of low strength and short working life,and are not suitable for energy harvesting in harsh environments.In this study,the geometric nonlinearity generated by the large geometric deformation of the structure itself is used to broaden the frequency band of energy harvesting and enhance the universality of the energy harvester in various environmental excitation bands.It can greatly improve the energy harvesting efficiency and make the energy harvesters more widely used.With the rapid development of composite materials,there are also a large number of researchers applying composite materials to energy harvesting.This topic uses multi-directional functional gradient materials(FGMS)to construct energy harvesting systems,which improves the load tolerance of structures subjected to multi-directional loads commonly found in engineering,thus enhancing the strength problem of harvesting systems.However,the introduction of multi-directional functional gradients(FG)increases the complexity of vibration energy harvesting systems,and it is necessary to enrich and develop nonlinear dynamics theories and methods,and study the nonlinear dynamics laws of complex systems,so as to propose optimization criteria with high energy harvesting efficiency.Taking the material properties continuously and smoothly varying across the axial and thickness directions of the substrate into account,Hamilton principle is used to establish the distributed parameter electromechanical model based on the geometric nonlinearity.The Galerkin truncation and the harmonic balance method combined with the arclength tracking continuation are applied to trace the frequency responses,which is compared with numerical solutions and the excellent agreement is obtained.The stability and bifurcation behaviors on the condition of resonance response interaction are predicted by the Floquent theory.Numerical example are disclosed that the effects of the excitation amplitude,damping coefficient,load resistance,axial and thickness FG index on the vibration displacement,output voltage and power.It is notable that the bifurcation behaviors of piezoelectric energy harvester may be tailored/tuned by multi-directional FG materials to achieve the wider frequency band and the higher harvesting power.