Improving the performance of electrowetting on dielectric microfluidics using piezoelectric top plate control

An intelligent EWOD top plate control system is proposed in this study. The dynamic top plate is controlled by a piezoelectric (PZT) cantilever structure. A High resolution laser displacement sensor is used to monitor the deflection of the top plate. The gap height optimization and the top plate vibration significantly improve the droplet velocity and decrease the droplet minimum threshold actuation voltage. The top plate vibration induced actuation velocity improvement is magnitude and frequency dependent. 100 μm and 200 μm vibrations are tested at 25 Hz. Vibration frequencies at 5 Hz, 10 Hz, and 20 Hz are tested while the magnitude is 200 μm. Results show greater improvements are achieved at larger vibration magnitudes and higher vibration frequencies. With a vibrated top plate, the largest reduction of the actuation voltage is 76 VRMS for a 2.0 μl DI water droplet. The maximum droplet instantaneous velocity is around 9.3 mm/s, which is almost 3 times faster than the droplet velocity without top plate vibration under insufficient driving voltages. Liquid that has different hysteresis such as acetonitrile with various concentrations are used as a control to show its compatibility with the proposed DMF chip. Contact line depinning under top plate vibration is observed, which indicates the underlying mechanism for the improvements in actuation velocity and threshold voltage. The top plate control technique reported in this study makes EWOD DMF chips more reliable when used for the clinical point-of-care diagnostic applications.