Research On Droplet Driving Technology Based On Surface Acoustic Wave

Because of its portability,controllability,and only a small amount of samples consumed,microfluidic system has aroused extensive attention in the fields of clinical medical diagnosis,drug delivery,and cell engineering.Microfluidic technology includes the manipulation of multi-phase and single-phase flow,continuous flow and droplets.Multiphase flow must overcome the problems of cross-contamination and separation of molecules,droplets or particles.Therefore,it is of great engineering significance for the manipulation of droplets that do not depend on the carrier fluid.Acoustic waves can realize various manipulations of droplets without a carrier fluid,such as driving,mixing,separation and screening of molecules or cells,and cell fragmentation.If the acoustic wave devices are integrated into the same chip with the power drive electronic circuit and microanalysis components,it is expected to realize a truly portable system-on-chip.Therefore,microfluidic systems based on acoustic waves,especially surface acoustic waves(SAW),are always an important research direction.This thesis mainly addresses the droplet driving principle based on surface acoustic waves and the role of important physical parameters such as the frequency of square-wave amplitude modulation(AM)signal,droplet viscosity,droplet size and excitation amplitude in the process of acoustic-liquid interaction.The main contents of this paper are as follows:First,COMSOL Multiphysics finite element simulation software is used to model and simulate the physical process of droplet driving based on surface acoustic waves.In the model,the piezoelectric material is 128°Y-X Li Nb O₃,the electrode is aluminum,and the droplet is water.The simulation work is mainly divided into two aspects.For the first-order linear acoustic problem,a two-dimensional physical model is established,and the leaky wave mode is verified by the thermoviscous acoustics module,and the obtained Rayleigh angle is consistent with the theoretical value.For the second-order nonlinear fluid dynamics problem,a three-dimensional physical model is established,and the incompressible laminar flow model is used to study the flow field structure inside the droplet.The obtained flow field structure further verifies the mechanism of surface acoustic wave accelerating the droplet mixing.Secondly,a surface acoustic wave interdigital transducer was designed and manufactured,and the experiment explored the relationship between the driving speed of the droplet and the volume of the droplet,the viscosity of the droplet,the frequency of square-wave AM signal and the amplitude of the excitation signal during the droplet driving process at a specific frequency.After processing and analyzing the experimental data,we found that:1)There is an optimal square-wave amplitude modulation signal frequency value for the droplet driving velocity.Experiments have found that the 6?L droplets get a bigger velocity when IDT is excited by a sinusoidal signal modulated by a 100Hz square wave under the same excitation level.2)The driving speed of the droplet increases with the excitation signal amplitude.3)There is a problem of the best matching between the effective size of solid-liquid contact surface and the wavelength of the excited surface acoustic wave.The experiment found that when d/?is around 8,there is a larger droplet driving speed.4)With the increase of viscosity,the driving speed of the droplet decreases dramatically.When the viscosity reaches a certain value,the down trend becomes slower and slower.This study proposed for the first time the influence mechanism of the square wave modulation signal frequency on the droplet driving rate.These laws have certain potential value for optimizing the application and development of microfluidic chips based on droplet driving.