Study On Micromixers That Regulate Concentration Gradient Of Solution In Real Time Under Bulk Acoustic Excition

Microfluidic chip is a device that accurately controls fluids at the micron or submicron scale,which aims for minimizing and concentrating the chemical analysis equipment used in the experiment,maximizing the integration of analytical laboratory functions on a millimeter-chip.Due to the fact that Reynolds number is so small in microscale that laminar phenomenon will happen in the microchannel,and different solutions mix slowly.The micromixer has become an important part of the microfluidic chip for rapidly achieving mixing the solution.The micromixer driven by bulk acoustic wave attracts attention of domestic and foreign scholars due to its simple structure,easy operation,good bio-compatibility,fast respond and so on.The existing micromixers driven by bulk acoustic wave cannot adjust the position of the mixing region in real time,has a poor control effect on the mixing solution in microfluidics system,and fail to generate stable and adjustable concentration gradients.This study proposed a micromixer which regulate the concentration gradient of solution in the channel by changing the position of acoustically oscillating bubble based on the permeability of PDMS.The tunable concentration gradient can be realized and mixing effects were produced in specific region through changing the numbers and positions of the bubbles that mix solution in the micro-channel,and the amplitude of the applied voltage.Besides,the influence of angle θ between the acoustically oscillating bubble in bubble channel and the main channel on the mixing effects is not clear.Therefore,this article explores the law between θ and mixing index by combining simulation analysis and experiments.The main research content of this paper is as follows:In the first chapter,the research background of micromixer at home and abroad was investigated,micromixers were classified according to the mixing principle,mixing performance parameter and working principle of different micromixer were concluded.The advantages and applied prospects of micromixer driven by bulk acoustic wave were analyzed.In order to realize regulating the position of mixing region in real time and get the relationship between the θ（between bubble channel that contains bubble and main channel that solution mixes）and mixing performance,the research schemes of micromixer driven by bulk acoustic wave were proposed.One was studying a three-point mixed micromixer that can regulate solution concentration gradient in real time,the other was researching on the multi-point mixing and the effect of θ on mixing performance.In the second chapter,the flow and mixing characteristics of solution at the microscale were analyzing,the microfluidic mixing mechanism were summarized.The working principles and methods of piezoelectric oscillators were studied,the selection of them was studied according to the demand condition of generating bulk acoustic waves.Using the permeability of PDMS and bulk acoustic excitation method to design a three-point mixed micromixer with regulating the solution concentration gradients in real time and a multi-point mixed micromixer that aims for studying the effect of θon mixing performance.The motion equation of the bubble under the oscillation of bulk acoustic wave was established and the producing mechanism of the acoustic streaming in the solution was analyzed.Based on the resonance characteristics of the bubble and the piezoelectric oscillator,the resonant frequency of acoustically oscillating bubble was calculated,and the scattering characteristics of the acoustic wave by a single oscillating bubble in the microfluidic were studied.In addition,the relationship between velocity of acoustic streaming and background velocity,microfluidics pressure and fluid density were studied according to the motion equation of the acoustic streaming.In the third chapter,COMSOL 5.3 A software was used to build the model of oscillating bubble in the bubble channel,the variation of the concentration gradients of solution with the velocity of the background field,the oscillating amplitude of the bubble and the number of the oscillating bubbles involved in mixing were studied.Besides,the influence of θ on the mixing performance of the micromixer were studied.The distribution figure of solution concentration was analyzed,the mixing index of mark position was extracted,and the influence of θ and flow rate on mixing effect were analyzed.In the fourth chapter,a three-point mixed micromixer layout that can regulate solution concentration gradient in real time was designed and the technological process was compiled.The sample of micromixer was fabricated by MEMS manufacturing processes.Designing and building the experimental test system,the mixed state of the solution was recorded and photographed with a microscope camera.Using MATLAB to process the experimental figures and analyzing the working performance of the micromixer.The variation of solution concentration gradient with driving voltage,bubble position and number of oscillating bubbles were studied.In the fifth chapter,researching plan on the multi-point mixing and the effect ofθ on mixing performance was proposed,four kinds of layout were designed by changing θ,using micro-processing technology to produce the sample of the multipoint mixing micromixer.Setting up the testing platform and conducting mixing experiments.Calculating the mixing index of specific location based on the concentration distribution of solution in micro-channel.The influences of bubble angle structure,driving voltage and inlet velocity on the mixing performance of micromixer were studied.