Theory And Technology Research On Ultrasonic Traveling Wave Microfluidic Driving

Microfluidic driving and controlling is the key basis technology of Micro total analysis system (μ-TAS). Ultrasonic traveling wave microfluidic driving is a new kind of technology. Compared with other mechanical and non-mechanical driving technology, it does not need pressure chamber and micro valve, and so it is easy to integrate and with high reliability. The controlling of flow rate and direction is flexible. Its flow pattern is different from the traditional pressure flow and the flow velocity close to the pipe wall is high, which can improve the efficiency of thermal diffusion. Its miniaturization can be used for drug release and implanted in the body, which has a unique advantage in the micro flow rate applications.To ultrasonic traveling wave microfluidic driving the wall vibration and flow pattern are very complex and there are many factors influencing the system. At the early stage of the study, which was the key force among peristaltic friction, acoustic streaming and radiation force had not been clear. The boundary of various factors had not been conclusive. Also the micro flow pattern and the appliance based on this principle were blank. In view of this, this paper had done comprehensive research on the ultrasonic traveling wave microfluidic driving. The generation of travelling wave in different model was studied. Three forces in ultrasonic traveling wave microfluidic driving including peristaltic friction, acoustic streaming and radiation force were analyzed. On this basis, fluid structure coupling problems in circular ring model were studied. Conclusion is drawn that acoustic streaming is the main driving force. A kind of H-type streaming micropump was designed and microfluidic pumping was realized on the basis of the boundary layer streaming. A kind of reflective streaming micropump was designed and the microparticles’transport was researched driven by acoustic streaming and radiation force. The main research work is as follows:1. The piezoelectric-structure-acoustic field-microfluidic multiphysics coupling model was established and the conclusion that acoustic streaming is the key factor was drawn. The feasibility of ultrasonic traveling wave microfluidic driving was verified by numerical analysis and dye microparticle tracer. Circular ring model was taken as the research object. The best model driving approach was determined through modal analysis. The micro-vibration displacement distribution of the fluid-structure-interface was obtained through harmonic response analysis and the traveling wave propagation was observed through transient analysis. Through fluid structure coupling analysis, the transient and the time-averaged velocity were computed and the influencing factors on the velocity were discussed. The results indicate that the transient velocity in the channel is sine shape and the time-averaged velocity profile is asymmetric parabolic shape. This parabolic shape is influenced by the driving frequency obviously. When the frequency is about2KHz to2.5KHz, the shape begins to change. At the same time the driving voltage has little impact on it. As the fluid viscosity reaches to0.07Pas, the reverse flow appears.2. A kind of H-type piezoelectric ultrasonic streaming micropump was designed based on the principle of boundary layer streaming and microfluidic pumping was realized through acoustic streaming. The influence factors on the average outlet velocity were analyzed. The acoustic streaming velocity vector in the micropump body was calculated through Direct Streaming Method and the body structure was designed optimally. The relationship between the average outlet velocity and the vibration displacement, driving frequency and the fluid viscosity was analyzed. Then the influence of back pressure on the average outlet velocity was simulated. The analysis results show that the average outlet velocity reaches4.87mm/s when the vibration displacement is0.1μm and the driving frequency is1MHZ. When the fluid viscosity is small enough, the average outlet velocity remains unchanged. When it is more than10-4Pa-s, the velocity decreases with the increase of viscosity. That is to say, when the fluid viscosity is small, the designed H-type ultrasonic streaming micro pump has excellent pumping performance. The average outlet velocity is directly proportional to the square of the displacement and the driving frequency. The pumping velocity can be controlled easily by changing the driving frequency or the driving voltage. The maximum back pressure of designed micropump is about135Pa.3. Microparticles’ transport driven by acoustic streaming and radiation force was realized preliminarily. A reflective acoustic streaming micropump was designed and the micropump structure model was proposed. The best driving frequency of1.154896×107Hz was determined from modal analysis. Then the acoustic pressure field and the acoustic instantaneous intensity distribution were studied. The streaming velocity in the pump chamber was calculated and the maximum velocity reached3mm/s. The maximum velocity of the suspended microparticles was1.0938mm/s and the influence factors on the microparticles movement were discussed. The microparticle movement is determined by acoustic streaming when microparticle diameter is less than2μm and the acoustic radiation force becomes dominated when microparticle diameter is more than5μm.