电检测液滴微流控闭环调节系统研究

To achieve high stable flow-rate supply of the droplet microfluidic systems, and increase the stability of droplet formation and the control precision of droplet size, the electrical-detection closed-loop control droplet microfluidic system is reported, where the pressure-driven device, the electrical-detection method and the droplet microfluidic system are integrated together in this project. The mechanism and mathematical model of the droplet formation in the T-junction microchannel are mainly studied. For high capillary numbers, the nonlinear model of the droplet size is established, and effects of the geometrical parameters of the microchannel on its nonlinear property are discussed. Meanwhile, for low capillary numbers, the linear relation between the droplet size and flow-rate ratio can be obtained. Especially, the pressure fluctuations at the T-junction which are induced by the process of droplet generation are demonstrated in this project, and the mathematical model of the pressure fluctuations is established. Based on the principle of electrical-detection method, by allocating couples of the microelectrodes along the microchannel, both the online detection speed and accuracy of droplet size will be increased significantly. By establishing the dynamic transfer functions of the electrical-detection closed-loop control droplet microfluidic system, the dynamic characteristics of the system can be simulated and tested. In particular, a specific controller is incorporated into the closed-loop control system and properly choosing the coefficients of the controller, the dynamic characteristics of the closed-loop control system can be improved. As a result, both the control speed and precision of the droplet size are increased drastically, which are quite important for the applications of droplet microfluidics in interdisciplinary study.

为实现液滴微流控系统稳定的流量调节，提高液滴形成稳定性和液滴尺寸控制精度，本项目将压力驱动装置、电检测方法与液滴微流控系统集成为一体，提出了电检测液滴微流控闭环调节系统。研究T型微流道液滴形成瞬态机理，当毛细管数较大时，建立液滴尺寸非线性数学模型，并分析微流道结构对非线性特性的影响，选取较小毛细管数，可得到液滴尺寸与流量比的线性数学模型。发现液滴形成瞬态过程引起微流道局部的压力脉动，通过分析微流道压力脉动形成机理，建立压力脉动的数学模型。基于电检测方法的测量原理，采用多组电极同时测量液滴尺寸，提高液滴尺寸的在线测量速度和精度。建立电检测液滴微流控闭环调节系统的动态传递函数模型，进行系统动态特性的仿真分析与试验测试，通过引入特定的控制方法并合理选取控制参数，改善闭环调节系统的动态特性，提高液滴尺寸的调节速度与控制精度，本项目研究对于开展液滴微流控系统在交叉学科领域的应用十分关键。

本课题主要针对液滴微流控系统，开展液滴形成基础理论、液滴尺寸电检测方法以及液滴微流控闭环调节系统研究。主要研究了T型微流道液滴形成的瞬态机理与数学模型，提出了液滴尺寸电检测方法并搭建了电检测液滴微流控闭环调节系统，实现了压力驱动装置、电检测方法与液滴微流控系统的集成。针对电检测液滴微流控闭环调节系统，重点开展了液滴形成瞬态过程压力脉动、液滴尺寸在线检测方法、液滴尺寸控制精度与液滴形成稳定性等研究工作。主要建立了液滴形成的数学模型、压力驱动装置的数学模型、瞬态压力脉动的数学模型、PDMS微流道数学模型和液滴尺寸电检测的数学模型。在低毛细管数下（毛细管数小于0.1），建立了液滴尺寸的线性化数学模型，为实现液滴尺寸的精确控制提供理论基础。研究液滴形成瞬态过程压力脉动的变化规律，可以抑制微流道局部的压力脉动，提高液滴形成稳定性与液滴尺寸在线测量精度。开展电检测液滴微流控闭环调节系统动态特性的仿真与试验研究，基于MatlabSimulink仿真平台，建立电检测液滴微流控闭环调节系统的动态传递函数模型，通过引入PID控制方法并合理选取PID控制参数，提高电检测液滴微流控闭环调节系统的动态响应速度和控制精度，实现液滴尺寸的在线检测与精确控制。液滴尺寸检测精度达到1μm，液滴尺寸控制精度达到2μm，液滴尺寸控制的相对误差小于2%。本项目的研究成果，对于开展液滴微流控系统在材料、生物与医学等领域的应用研究，促进交叉学科发展，具有重要意义。