Spatial alignment and functional manipulation of droplet-based systems

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Control of liquids became an important topic in microsystems technology at least over the last decades. Conventional liquid actuation e.g., by membranes or micro-turbines has been replaced by non-mechanical concepts based on electrostatic field effects. In this context, the movement of liquids has so far been limited to a 1D-(electrocapillarity) or a 2D-approach (EWOD, digital microfluidics). Based on our studies on droplet manipulation from the first funding period, electrostatic optofluidics will be extended to a controlled full 3D motion of droplets. Furthermore, the spatial arrangement of electrodes will allow a droplet shape control and therefore a change in the refraction. An optical array with optofluidic elements like an anamorphotic zoom is obtained that can be configured freely. This optical array consists of stacked multi-electrode arrays on perforated plates, that allows to move droplets through a 3D framework with stable rest positions, comparable to a high rack storage for droplets. The key challenge is to enable an independent movement of droplets in all spatial directions within a single layer and between two layers. This requires a sufficient arrangement of cooperating electrostatic actuators as the 2.5D-technology does not allow fully symmetric 3D arrangements. The coordinated interaction of stacked layers will offer the opportunity to shape individual droplets by differential electrostatic fields. This offers the opportunity to investigate advanced optical applications, which require for example crossed optical axes, synchronous actuation of multiple fluid lenses at the same time or a dynamic reshaping of fluid lenses. Because of the sophisticated shape of the electrical field within the proposed 3D actuator and its complex geometry, which implies a challenging calculation of surface energy, a classical white box modeling is not possible for the proposed system. Therefore, we will develop a novel identification algorithm, which iteratively uncovers the system topology and identifies the system parameters. The result will be a flat state space model and thus the use of flatness based closed loop control approach will be possible. This research will enable the use of fluid lenses in application, which need multiple highly adjustable lenses. By building up a demonstrator of a high rack storage like optofluidic micro actuator and investigating coupling effects and special features of droplets within a mesh of cavities a testing platform for optofluidics is created. Using advanced control technologies developed within this project will enhance the performance within optofluidic applications and will expand their application area to dynamic task like motion tracking or LIDAR.