Research On The Coupling Characteristics And Injection Performance Of Piezoelectric Micro-jet

The piezoelectric micro-jet is a kind of micro-electro-mechanical device which is based on the piezoelectric inkjet technology and developed by extending the type of the ejected fluid.Pressure waves are created at the fluid-solid interface by piezoelectric vibrator when external pulse voltage excitations are applied,the droplets are pushed out of the nozzle by the pressure waves which are propagating through fluid medium to the nozzle.With the advantages of simply structure,quick response and high precision,the piezoelectric micro-jet is wildly used in many industrial fields,such as biomedical,circuit and electronic,chemical and additive manufacturing.In order to improve the working performance of the piezoelectric micro-jet,researchers analyze the related parameters which affect the injection performance,so as to give the references for selecting the related parameters to improve the injection performance.Now days,the analyses of the performance of the piezoelectric micro-jet are mainly for analyzing several parameters of the nozzle part,and the analysis methods are usually not universal.Thus,the performance of the relatively more universal piezoelectric micro-jet are analyzed in this work.Theoretical models for each working stage of piezoelectric micro-jet mechanism are established.The working mechanisms of piezoelectric micro-jet are revealed.According to the analysis results,the selection methods of parameters for obtaining required working performance are obtained.Firstly,the acoustic pressure wave propagation model in the cavity is established.Based on the model,the acoustic structure coupling analyses for piezoelectric micro-jet with traditional structure form are carried out in this work.The acoustic structure coupling mechanisms between piezoelectric vibrator,shell and fluid in the cavity are revealed.The influences of key structural dimensions,shell materials,velocity of acoustic wave in fluid,and working frequency on nozzle pressure and reaction force of vibrator are analyzed.The selection principle of key structure size,shell material and working frequency for obtaining the desired ejection performance are obtained.A model for analyzing the forming process and motion characteristics of droplet is estabished.Based on the model,two phase flow coupling analyses with cavity fluid domain in consideration are carried out.The influences of pulse voltage excitation parameters and physical properties of fluid on the droplet forming process and motion characteristics are alalyzed.The recommanded excitation parameters for obataining different injection performance requirements are given,and the adjustment schemes of the excitation parameters to stabilize the ejection performance,when the properties of the ejected fluid changes,are provided.A novle piezoelectric micro-jet which is used for bearing lubrication is proposed,the acoustic coupling analyses and tow phase coupling analyses are carried out.The influences of pulse voltage excitation parameters and physical properties of oil on injection and lubricationg performance are analyzed.The recommanded excitation parameters are given for obtaining high inje ction and lubrication performance.A model for analyzing the spreading oscillation characteristics of droplet on the target surface is estabilished.Based on the model,a piezoelectric micro-jet wihich can be used for printing is analyzed.The spreading mechanism of droplet is revealed,and the spreading characteristics of the droplet when moving to the target surface under different conditions are analyzed.The recommanded excitation parameters for obtaining high spreading precision and avoiding failure spreading are given.In this paper,based on the established theoretical model which describs the working mechanism of the piezoelectric micro-jet,the numerical simulations are carried out to analyze the effects of parameters on the performance of the piezoelectric micro-jet.The realtive working mechanisms are revealed and the corresponding analysis results are obtained.The prototypes are manufactured and experiments are carried out,and the experimental results verify the validity and credibility of the obtained results.As there is no more additional restrictions in the method,the analysis results can be used as references for performance improvement of the esisting desinged piezoelectric micro-jet.