Research On Multi-Flied Coupling Modeling And Digital Simulation Of A Piezoelectric Valveless Micropump

With rapid development of micromachining technologies, microfluidiccontrol systems, with properties of miniaturization, automation, integration,intelligence and batch-processing, have been widely studied and used inacademia and industry. It is believed that the new technology (e.g. BioMEMS)will lead to a revolution in the fields of life science, medical research andchemical analysis. As an important element, the driving sub-system of amicrofluidic control system determines its functionality of the entire system.The long-term and highly reliable applications of a microfluidic controlsystem depend on the highly efficient and stable performance of its drivingsub-system (e.g. micropump). Currently, the study on the driving sub-systemsof microfluidic control systems is mostly focused on the working principlesand their micromachining processes, but the research on fundamental theoriesof modeling and analysis of micro devices are still at the primary stage. Thesefactors bring a great challenge for the design and analysis of drivingsub-systems, limit the development of microfluidic control systems, and mayeven delay the transfer between the experimental models and the practicalproducts.In this thesis, a piezoelectric valveless micropump commonly used inthe microfluidic control system is studied. To understand the behaviors of thepiezoelectric valveless micropump and its components (mainly including piezoelectric actuator and microdiffuser/micronozzle), the multi-physicalfield coupling modeling and digital simulation method is presented.Because of various, complicated mechanical behaviors of thepiezoelectric valveless micropump, there are a lot of debates on the researchof fundamental theories for its modeling and analysis. Some key open issueson the theory development include:①Because of the improvement of themicrodevices integration, and the coupling effects with multiple disciplines,multiple processes and multiple variables are strengthened, it is difficult touse the analysis methods and design standards from one single discipline forthe analysis of microsystems.②The applicability and available scope of thecontinuum model should be discussed further.③Due to the reduction of thecharacteristic sizes, it is difficult to exactly observe the output properties ofthe driving sub-system and its microflow phenomena, and to predict itsbehavior during the initial stage of the system design In this case, it isimportant to develop the simulation technology.In this thesis, some theoretical and technological problems about thedesign of piezoelectric valveless micropumps with the multi-disciplinary andmulti-variable coupling effects are studied. The coupling model (mainlyincluding electro-solid and fluid-solid coupling) of the valveless micropumpis systemically discussed by using the combined methods of theoreticalanalysis, finite element simulation and physical experiment. Furthermore, themulti-field coupling model and its digital simulation are presented. Thedesign environment based on the UML and digital simulation is also explored.The research results can provide the theoretical reference or instruction forthe design and fabrication of the piezoelectric valveless micropump. Themain contents and contributions of this research work include:1. Improvement on the electro-solid coupling model which enhances the integrity of the modeling theory.①Based on thepiezoelectric coupling theory and the assumption of the equivalent laminatedplate model, the general coupling model for the piezoelectric actuators,including the stacked circular piezoelectric actuator and circular unimorphactuator, is presented. This extends the application of the equivalentlaminated plate model from the symmetrical piezoelectric actuator tounsymmetrical piezoelectric actuator.②For simplifying the analysis of thecoupling model, the coupling variation model of the unimorph actuator ispresented based on the energy variation principle and piezoelectric couplingtheory, which improves the accuracy of the current variation model.2. Analysis and its optimal design of the coupling performances ofthe piezoelectric actuator based on numerical simulations and physicalexperiments. The static and dynamic properties of the piezoelectric actuatorare analyzed by numerical simulations and physical experiments, and theavailable range for the general coupling model and variation coupling modelabove are discussed. The results show the effect of the structure parameters ofthe piezoelectric actuator on the deflection. It is found that there is an optimalsize parameter for the piezoelectric actuator to achieve the largest deflection.3. Establishment of the electro-solid-fluid coupling variation modelsuitable for the problem with the combined effect of the electrical,mechanical and fluid fields. The electro-solid-fluid coupling variationmodel is presented based on the variation coupling model of the piezoelectricactuator, Reynolds transportation equation and energy loss theory. Moreover,the equation of output properties and the first natural frequency for thepiezoelectric valveless micropump are derived, and the effect of the changeof the pump chamber on the properties of the piezoelectric valvelessmicropump is discussed. Compared with the current, simplified model for the valveless micropump, the new coupling model can represent the entireperformance of the micropump, which provides a new method for theanalysis of the piezoelectric valveless micropump.4. The numerical analysis and simulation method for themicrodiffusion characteristics of the diffuser/nozzle element and thepiezoelectric valveless micropump. The finite element model of themicrodiffuser/micronozzle is modeled by ANSYS software. The flowproperties in fluid field are simulated, and the results show that the structuralparameters and flow status for the diffuser/nozzle element have effect on themicrodiffusion. The simulation model of the piezoelectric valvelessmicropump is built. By simulation the output characteristics of thepiezoelectric valveless micropump are systematically analyzed, and theoptimal designs are determined. The simulation method for the piezoelectricvalveless micropump can be used for solving the problems resulted from theabsence of the electro-solid-fluid coupling simulation.5. Exploration of the application design of the piezoelectricvalveless micropump in the drug delivery, and the design method andtheory combining the numerical simulation and UML for the designenvironment of the microfluidic control system. The application design ofthe piezoelectric valveless micropump for treatment of the diabete patient isstudied. To model the system design and achieve a quick design ofmicrofluidic control system, a systematic modeling and design method basedon the finite element simulation and Unified Modeling Language (UML) ispresented. The static and dynamic models for the microfluidic control systemare built, which represents the topological relations, informationtransmissions, and system functions among the devices/sub-systems in themicrosystem. The design software of the piezoelectric valveless micropump is developed, and then the validation of the design theory is verified. Thedesign method combining the design model, coupling analysis and numericalsimulation provides a way for the study on the design standard of themicrofluidic control system.