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Enhanced addressability and localization in digital microfluidic multiplexer systems Abolhasani, Milad


This research presents a novel digital microfluidic multiplexer structure based on a cross-referencing architecture. The new multiplexing technique uses bi-polar voltage activation and threshold effects to overcome addressability limitations and eliminate inter-microdroplet interference. Fan et al. in 2002 introduced cross-referencing for enhancing addressability. The technique uses two sets of rectangular electrodes: top rows and bottom columns. Such a system achieves m+n addressability with only m+n electrodes. This is a significant achievement as voltage addressing and microdroplet actuation are performed by the same linear electrode structures. There remains one major drawback to the conventional cross-referencing method. Desired motion of a microdroplet on an electrode grid can result in undesired motion of other microdroplets placed on the same electrode row. Other groups have proposed intriguing solutions to this problem with cascaded differential voltage activation and graph theory, respectively. However, these methods become increasingly complex for systems with multiple microdroplets, as the solutions for addressability must have a limited number of microdroplets. The proposed method introduces a new multiplexing format for cross-referencing of DMF systems through the simultaneous use of threshold-based voltage actuation (which sets a minimum voltage to initiate microdroplet motion) and bi-polar voltage activation on the overlying and underlying electrodes. The threshold voltage effect for requirement one has been characterized numerically and experimentally, and the results are presented here. With regard to requirement two, it is necessary to employ a voltage addressing scheme that can preferentially isolate overlapped regions of the 2-D grid. This goal can be achieved using a bi-polar electrode activation technique, as the bi-polar DMF multiplexers will have a ±2Vapp voltage difference in the overlapped location and only a maximum of ±1 Vapp voltage difference in all other locations. This relationship has been quantified using an electrostatic 3-D COMSOL model of the proposed DMF multiplexer. A fabrication recipe for the proposed DMF multiplexer system is reported in this research, and the multiplexing protocol has been studied experimentally to verify the numerical analyses. The proposed technique with this threshold-based bi-polar activation can improve mxn addressability with multiple microdroplets in a cross-referenced DMF grid.

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