Electrowetting On Dielectric Driven Digital Microfluidics Simulation Research

Digital microfluidics technology which is recently booming comes from the combination of microfluidics and MEMS and reflected the trend of SOC. Its research is apt to integrate the optical, mechanical, electrical and fluidic component to one chip. For digital microfluidics system, the future industrialization roadmap is to integrate the droplet sample processing function, sample inspecting function, system environment adjusting module and embedded controlling software. The system environment adjusting module covers temperature controlling, humidity controlling, pressure controlling, etc.. Digital microfluidics system which is based on EWOD (electrowetting on dielectric) principle is intent to digitalize the fluid to single droplet to manipulate. With the aid of electrodes array, quantitive control, sequential control and parral control can be realized. The droplet sample processing function of droplet generating, transporting, merging and splitting can be integrated in a single chip.Aiming at the EWOD based digital microfluidics, computer aided numerical simulation technology is adopted to investigated thoroughly the droplet driving technology in the system. The research contents covers the electric field analysis and simulation and droplet simulation with the multiphase lattice boltzmann algorithm. The target of the simulation is to deeply understand the system behaviour and lay a basis for the system design and optimization. The main work of this dissertation is summarized as following:1. The state of the art in digital microfluidics system in oversea and domestic region is reviewed. the characterics and main technologies in continuous microfluidics and digital microfluidics is assessed extensively. Pressure driven, electroosmotic and electrophoresis mechanism are utilized in the continous microfluidics. While EWOD, dielectrophoresis, electrostatics, surface acoustic wave, thermocapillary, magnet and light are exploited in the digital microfluidics. Additionally, the products based on the electrowetting and relevant research institudes are introduced. Further, advancements in both experiments and simulation of EWOD based digital microfluidics is evaluated deeply. The application of lattice boltzmann simulation algorithm in multiphase fluid is introduced.2. The EWOD system is investigated. The EWOD theory which contains Lippmann–Young equation, contact angle saturation phenomean and the droplet driven mechanism is discussed. Three configurations in the EWOD system are analyzed and compared in details. Relevant important technologies in integrated EWOD system is clarified which includes the system configuration, power supply and capacitive detection, etc. PCB process is also attempted to make electrode arrays. These works lay a foundation for the actual prototype design.3. In the light of governing equation of fluid field and electric field in the EWOD system, solving methods and physical model are clarified. The electric field of the system is analyzed and simulated. The analysis of the Debye length in the electrical double layer shows that the electrical double layer affects little to the EWOD system. The simulation result of the electric field shows that the intensity of electric field inside the droplet is weak and changes with the droplet's movement and transformation. In the process of droplet's movement, electric field of the dielectric covered by droplet is intensest, while electric field of the dielectric uncovered by droplet is almost zero. So the dielectric contacting with the electrodes bears the effect of alterating electric field. The simulation method and result will further contribute to the system design and optimization.4. the application of lattice boltzmann model and surface tension model advanced by Shan and Chen in the simulation of droplet driven by EWOD is thoroughly researched and the way to dynamic controlling of fluidic surface tension is put forward. On the basics of theory research, the design process of lattice boltzmann transient simulation program and steady simulation program is summarized and simulation program is developed.5. Based on the lattice boltzmann algorithm, simulation research is as followed. Firstly, roplet shape in initial time is evolved with steady calculation program. Besides, aiming at the basic operation of square wave voltage signal action, the average velocity response of droplet to the single square wave voltage signal is investigated. The parameters of the initial relative position of droplet and electrode, the width square wave signal and the gap between the top and the bottom board are studied. Thirdly, the simulation process of acting of time sequence square wave signal to droplet is described in details. The effect of interacting force between fluid and solid surface to the average velocity and the wetting length between upper and lower interface in droplet driven process in closed asymmetric electrode configuration is simulated. In addition, according to the characteristics of EWOD, the pros and cons of three configurations of EWOD is compared and the droplet shape evolving process and driving velocity is compared in these configurations by numerical simulation. The results indicates that the configurations affect the performance of driven droplet greatly. These simulation results provide a reference to the structure design and the time sequence control design of square wave signal in EWOD based digital microfluidics.6. The dissertion is surmarized and future research is prospected. Firstly, upon the understanding of the effect of electrostatics and AC to the system, the coupling of electrical field and fluidic field needed to be thoroughly investigated in theory. Additionally, on the basis of theory research and integrated chip design & optimization , the prototype needs to be realized and the system performance testing and characterization need to be done by experiments. What's more, biochemical samples need to be handled and analyzed on the platforms of EWOD based digital microfluidics. At last, when the prototype testing and the samples experiments are finished, the products development and mass manufacturing technologies are to be studied in the light of the market.