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Proceedings Paper

Size dependent droplet actuation in digital microfluidic systems
Author(s): Biddut Bhattacharjee; Homayoun Najjaran
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Paper Abstract

Digital microfluidic systems (DMFS) manipulate liquid droplets with volumes in submicroliter range in two dimensional arrays of cells. Among possible droplet actuation mechanisms, Electrowetting-on-dielectric (EWOD) actuation has been found to be most feasible and advantageous because of low power consumption, ease of signal generation and basic device fabrication. In EWOD based DMFS, droplets are actuated by applying an electric field and thus increasing the wettability on one side of the droplet. In this paper, we show that the EWOD actuation of a droplet can be modeled as a closed loop system having unity feedback of position. Electrode, dielectric and droplet are modeled as a capacitor with variable area as the droplet, considered as a conductor, moves over the dielectric layer. The EWOD force depends on the rate of change of droplet area over the actuated electrode, which in turn depends on the direction of motion and the position of the droplet between the actuated and previous electrode. Thus, EWOD actuation intrinsically utilizes the droplet position to generate sufficient force to accelerate the droplet. When the droplet approaches the final position, the magnitude of force reduces automatically so the droplet decelerates. In case the droplet has sufficient momentum to exceed the final position, the EWOD force, according to the model, will act on the opposite side of the droplet in order to bring it back to the desired position. The dynamic response has been characterized using the proposed model for different droplet sizes, actuation voltages, dielectric thicknesses and electrode sizes.

Paper Details

Date Published: 11 May 2009
PDF: 12 pages
Proc. SPIE 7318, Micro- and Nanotechnology Sensors, Systems, and Applications, 73180H (11 May 2009); doi: 10.1117/12.818031
Show Author Affiliations
Biddut Bhattacharjee, Univ. of British Columbia (Canada)
Homayoun Najjaran, Univ. of British Columbia (Canada)


Published in SPIE Proceedings Vol. 7318:
Micro- and Nanotechnology Sensors, Systems, and Applications
Thomas George; M. Saif Islam; Achyut K. Dutta, Editor(s)

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