Electrical-detection droplet microfluidic closed-loop control system for precise droplet production

To precisely control the size of the droplets is quite important for the application of the droplet microfluidic systems. To date, the size of monodisperse droplets is usually measured by the method of image processing for droplet microfluidics, which requires expensive detection devices such as microscope and high-speed camera. In this paper, an electrical-detection droplet microfluidic closed-loop control system is demonstrated, where the flow rates of fluids are controlled by the pressure-driven microfluidic device and the droplet size can be obtained from the method of electrical detection. The mathematical model of the closed-loop control system is established. Compared with the method of image processing, both the measuring efficiency and accuracy of the droplet size are increased significantly by the electrical detection method, which can improve the dynamic characteristics of the droplet microfluidic closed-loop control system. In particular, a PI controller is integrated into the closed-loop control system to improve the control precision of the droplet size. By varying the flow rates of the fluids, the effects of the droplet production rates on the dynamic characteristics of the closed-loop control system are studied, and the control precision and stability of the system can be obtained from the experimental measurements. (C) 2017 Elsevier B.V. All rights reserved.