Research On The Preparation Of Piezoelectric Capillary Droplets Based On Centrifugal Force

With the development of biochemical technology,microfluidic technology based on droplet preparation has attracted more and more attention.Depending on whether microfluidic chip is used as microfluidic device,microfluidic droplet preparation technology can be divided into microfluidic chip technology and off-chip technology.Because the fabrication of microfluidic chip requires lithography,thin film deposition and other micro-processing technologies,the cost is high,and the off-chip technology requires additional driving equipment,which is difficult to miniaturize,limiting the popularization and application of droplet preparation technology.In this paper,in order to balance fabrication cost and miniaturization,an off-chip piezoelectric capillary droplet preparation technology based on centrifugal force is proposed.Piezoelectric single-chip is used as the driving device,and stainless steel capillary is used as the microchannel to generate droplet with a radius of 1.283 mm?0.176 mm and droplet preparation rate is up to 113 ul/min.The droplet size was controlled by controlling the driving voltage,excitation frequency and the output flow rate of the injection pump.The droplet generator can directly prepare droplet from the tip of capillary tube without the assistance of other liquids.It has low production cost and simple operation,and has certain application potential in biology,medicine and other fields.The specific research contents are as follows:(1)A mechanism of droplet preparation based on centrifugal force was proposed.For piezoelectric single chip input sine excitation signal,piezoelectric single-chip vibrating and applying vibration excitation to stainless steel capillary,due to the coupling vibration modal,the ellipse trajectory of free end capillary is produced,cause the high-speed rotation of the droplets,the centrifugal force overcomes the surface tension and the droplets is generated.(2)Design and simulation of vibration system.By analyzing the eigenfrequency of the capillary,the working frequency and vibration excitation position of the capillary are determined.By analyzing the eigenfrequency of the elastic wafer,the bonding position of the piezoelectric ceramic wafer was obtained,and the finite element analysis of the piezoelectric single-chip was carried out.By means of frequency domain finite element analysis,the eigenfrequency and output characteristics of the vibration system composed of piezoelectric single-chip and capillary are preliminarily determined.(3)Vibration output characteristic test of vibration system.The impedance characteristic curve of droplet preparation device was obtained by impedance analyzer.A laser displacement sensor was used to measure the amplitude of the output end of the capillary tip and the piezoelectric single-chip with the change of frequency.Because of the principle of local resonance,the capillary can vibrate alone and obtain a larger amplitude.Because of modal coupling,the free end of capillary generates elliptical trajectory vibration.(4)Droplet generation performance test experiment.The experimental platform of droplet preparation performance was set up and experiments were carried out.The curves of droplet preparation radius-voltage and fracture speed-voltage were obtained,and the droplet generation performance was preliminatively studied.In order to further analyze the droplet preparation mechanism,the variation of droplet rotation speed with time during droplet formation was studied.Finally,the variation of droplet radius with excitation frequency and injection pump output flow rate is studied.