MEMS micropump characterization and control utilizing a fibre optic interferometer

In order to successfully integrate microdevices into functional systems, it is often important to address issues of real-time performance monitoring and control. The present study addresses some of these problems in the context of a piezoelectric-driven micropump. These devices are important for emerging areas of chemistry and medicine where reliable distribution of small quantities of fluid is required. A simple, low-cost, fibre optic interferometer has been used to measure the dynamic displacement of the micropump actuator surface. Measurements show significant differences in actuator velocity, displacement and settling time between different pumping media. In addition, transient underdamped vibration of the actuator surface was observed during the rapid excursion and recursion phases of the pump movement while pumping air. These non-contact measurements can be used to determine the open loop characteristics of the micropump and provide information for design improvement or failure analysis. However, the technique can also be used to provide continuous measurement for adaptive compensation, so that the pump performance criteria are always satisfied. To this end, an automated interference fringe counting algorithm has been developed, so that the steady-state parameters can be mapped into the closed-loop control elements in real time. The performance of this algorithm will be discussed, together with the implications for optimal control of the micropump and eventual integration of the interferometer and micropump systems.