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(a) Schematic of partially filled electrodes providing space for additional on-chip tools or as a window for imaging. (b) Example designs of partially filled electrode configurations considered. Electrodes are 1 mm × 1 mm (c) Image of droplet on series of partially filled electrodes.
Simulation results. (a) Droplet half space mesh and swept uniform mesh on droplet surfaces. (b) Actuation force on droplet for conventional electrode on leading and trailing droplet surfaces. Reverse actuation force is generated on trailing droplet surface as backward interface begins to move onto electrode. (c) Induced forces increase linearly with electrode fill ratio, which was changed by varying the width of the horizontal bars in the electrode. (d) Force is independent of vertical location of removed area from electrode. The leading edge of the droplet is fixed at the midpoint of the electrode for panels (c) and (d).
(a) Simulation results: electrode design with crescent-like filled areas at the entrance and exit of the electrode produces increased force at beginning and end of droplet motion to create initial force to ensure droplet motion is generated. (b) Experimental comparison of electrode designs. In experiments, maximum droplet actuation frequency was measured at different fill percentages for normal and improved designs. Number of horizontal bars in the electrode was kept constant, thus reducing the bar width, reduces electrode fill percentage. Please note that reduction in maximum actuation frequency is almost proportional to the reduction in the bar width similar to the force reduction simulations. Experiments were conducted with deionized water at 75 V rms and 15 kHz by actuating droplet back and forth across a series of 5 electrodes at increasing speed until droplet motion could not keep up with actuation.
(a) Single mouse embryo morphology on partially filled Cr electrodes. Upper image uses bright field transmission DIC imaging showing superior detail compared to reflection microscopy imaging used in lower image. (b)RBC viability measured with different osmolarities by counting cells through unfilled regions on chip. N = 150–600 for each osmolarity point.
Parameters used in numerical simulation.
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