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Design and fabrication of unsteady electrokinetic microactuator arrays for turbulent boundary layer control

The development of a micro-electro-kinetic-actuator (MEKA) array for the study and control of the viscous sublayer of a turbulent boundary layer is presented. Several generations of such MEKA arrays have been fabricated that explore the use of non-conventional MEMS materials such as quartz, polymers or mylar and are combined where needed with conventional MEMS design and fabrication processes. The present study is the first attempt to exploit the potential advantages of using the electrokinetic principle as the basis for a new class of microscale actuators suitable for active sublayer control. Among such advantages are that these actuators have no moving parts, and that they achieve the flow rates required for this type of flow control. Moreover, the inherent problem of matching the length and time scales between microactuators and the physical system being controlled makes the viscous sublayer a natural choice for these types of actuators. The electrokinetic drivers are fabricated inside microchannels, 250 mm to 2 mm in diameter, using a liquid-phase polymerization process that generates 1 µm doped pores. This process greatly simplifies the fabrication of a large number of actuators, and using this technique we are able to fill 100% of the 25 600 microchannels that form the typical MEKA 5 array. The array is fabricated using a novel three-layer design that contains (i) a top layer with the actuator nozzles, electrodes and leadouts, (ii) a center layer containing the individually addressable electrokinetic driver channels in which electrolyte pumping occurs in response to a time-varying electric field that will induce volume displacement in the sublayer and (iii) a bottom layer containing an electrolyte reservoir and common electrode. The functionality incorporated in this three-layer design with independent unit cells demonstrate all the elements needed for turbulent boundary layer control.