| Lab-on-a-chip technology is based on the integration of microfluidics for liquid handling with miniaturized analytical devices or diagnostic instruments for the performance of chemical/biomedical protocols. In this dissertation, timing-based dynamic control and optical-sensing based feedback control are developed based on dielectrophoretic (DEP) microfluidics.; A dielectric-coated three-electrode device with a T-junction gap is fabricated as a platform for liquid finger actuation and trapping using AC voltage. Upon voltage removal, capillary instability breaks the trapped finger into uniformly spaced droplets following Rayleigh's theory. Several sets of electrode dimensions, T-junction configurations, and coating materials are tested, and their influences on actuation voltage, finger profile and droplet formation uniformity are examined to optimize actuation reliability.; DEP finger actuation is modeled by lumped electromechanics, and a reduced-order hydrodynamic model that incorporates contact line friction. The predicted dynamics is least squares fitted to the experimental data, yielding contact-line-friction coefficients. Based on the prediction, an open-loop scheme using timing control is developed for control of trapped finger length and droplet number. This scheme realizes functional droplet metering; however, it is very limited and not suitable for precision microfluidic systems.; To overcome the limitations of open-loop control, an optical sensing-based feedback control system is developed on DEP coplanar devices. In this closed-loop scheme, a programmable control module applies voltages to manipulate liquid; optical signals, detected by a sensing circuit, are fed back to the control module. Test results obtained from various control strategies are presented. In the single-sensing scheme, the finger profile is maintained to avoid mass redistribution, so the trapped length and the droplet number are controlled only by sensor location. In the multiple-sensing scheme, model predictive feedback control is implemented to achieve real-time dynamic control according to feedback signals. Combining feedback control with timing control enhances DEP coplanar devices with hybrid control capabilities, such as microfluidic switching controlled by voltage-on/off valving, droplet dispensing and oscillatory-driven transport controlled by DEP and EWOD, respectively.; Feedback control and control strategies exhibit very interesting capabilities for novel intelligent microfluidic systems and for eventual implementation in the lab-on-a-chip. |
