Theoretical And Experimental Study On Microscopic Deformation Of Piezoelectric Materials And Multi-source Energy Harvesting

The piezoelectric energy harvesters based on environmental vibration have attracted the attention of many scholars,however,most piezoelectric energy harvesters are the single degree of freedom linear system and only have high power output at the resonant frequency.The output power decreases rapidly once the vibration deviates from the resonant frequency.In this work,two novel piezoelectric energy harvesting structures are proposed to improve the conversion efficiency,broaden the working frequency band and enhance the environmental adaptability of piezoelectric energy harvesting.At the same time,the surface micro-deformation of piezoelectric materials is introduced into the energy harvesting system,and a multi-vibration source energy collection scheme is given to solve the problem of environmental adaptability effectively.The main work of this dissertation is as follows:(1)An energy harvesting scheme of micro deformation on the surface of piezoelectric materials is proposed.To overcome the shortage of piezoelectric vibration energy harvester must through the rectifying circuit to output electric energy and energy loss.Based on the piezoelectric surface theory,the two-dimensional contact model of piezoelectric materials in the indentation process with different shapes of indenters is established.In addition,the contact deformation and surface potential of 15 different thicknesses of piezoelectric materials under the rigid flat indenter are studied.It is discovered that for the same indentation depth,the surface potential of piezoelectric material increases with the decrease in piezoelectric material thickness.The potential generated by the deformation depth at the micro-nano level is consistent with that generated by the vibration of a piezoelectric cantilever beam,which can meet the basic requirements of the piezoelectric energy harvesting.(2)Aiming at the singularity of stress and electric field at the contact edge in micro deformation of piezoelectric materials,the indentation behaviors of rigid non-piezoelectric materials and piezoelectric materials on the piezoelectric material substrate under quasi-static and dynamic conditions are studied.The results suggest that the surface potential of the piezoelectric substrate is only related to the indentation depth.And it has a linear relationship under the two motion states.Through the study of micro deformation displacement function,electric field distribution,and the relationship between indentation depth and potential,it is found that there is singular stress at the contact edge,and the damage to the material is slight.Furthermore,the electric field singularity is helpful to increase the potential of micro deformation surface,so as to reach the design requirements of energy harvesting system.(3)The gradient composite piezoelectric energy harvesting model is proposed based on the Euler-Bernoulli beam equation,piezoelectric equation and Kirchhoff laws.The coupling voltage and electromechanical response equations of the gradient composite piezoelectric energy harvesting structure with multiple lumped masses are derived by combining with the matching frequency bandwidth method between the piezoelectric energy harvester and the vibration source in the environment.The influence of structural parameters such as piezoelectric plate,the base beam and the lumped mass on the voltage output of the piezoelectric energy harvesting system is analyzed.Its' optimal system is also discovered.The results indicated that there are three output the voltage peaks in the 100 Hz working frequency band range,which not only achieve the effect of wide-frequency energy harvesting but also improve the output voltage of gradient composite piezoelectric energy harvesting system.(4)A multi-modal variant structure composite piezoelectric energy harvesting system model is developed to solve the single-mode problem in energy harvesting,which can achieve high electric energy in a low-frequency range.By analyzing the influence of the structural parameters of the composite piezoelectric energy harvesting structure on the system's natural frequency.It is found that with the increase the length of the beam and the decrease the width,the natural frequency of each order of the system decreases,however,with the increase of the angle among the beams,the first natural frequency has a peak value,and the third natural frequency tends to be stable when the angle exceeds 70 degrees,which meanings that the energy harvesting system can use multi-modal vibrations to collect energy in the low-frequency range,and the minimum peak voltage exceeds 5 volts.(5)A new multi-source composite piezoelectric energy harvesting system is proposed to solve the problem of low efficiency of piezoelectric energy harvester under the excitation of complex multi-environment vibration sources by combining the theory of the gradient composite piezoelectric energy harvester and the generation mechanism of micro-deformation electric energy of piezoelectric materials.The working bandwidth through the combination of multiple cantilever beams and lumped masses is increased in the piezoelectric energy harvesting system.For example,the displacement of the lumped mass at the end of the beam into a low-density material can achieve the vibration following the airflow and increase the matching width with the excitation source.Through the experimental study of the impact process of micro-particles on the surface of piezoelectric materials in natural environments such as raindrops and fine sand dust,the feasibility of micro deformation energy harvesting of piezoelectric materials is verified.The results showed that the new multi-source composite piezoelectric energy harvesting system could broaden the working frequency band and match the vibration source of the complex environment to harvesting energy,as well as change the electric energy output way to achieve the near-DC output effect.In summary,the new piezoelectric energy harvesting structures proposed in this dissertation can not only efficiently output the power with broadener working frequency but also provide a new method for the piezoelectric energy harvesting,which has a good application prospect.