We have previously developed a microparticle sampling method in which electrowetting-actuated droplets sweep and pick up microparticles trapped on a perforated membrane. In this configuration, a critical issue is to increase the opening ratio (ratio of opening hole area to the total membrane area) in the perforated membrane as much as possible since the higher the opening ratio the lower power consumption in the process of air suction. In contrast, increasing the opening ratio hampers successful electrowetting operations of droplets and thus sampling of microparticles. In this study, we analytically investigate effects of the opening ratio on electrowetting operations. In particular, we are looking at the reversibility of electrowetting operation. Then, we fabricate testing devices to verify the analytical results in the range of the opening ratio up to about 90%. We will also discuss detailed challenging issues in microfabrication to reach such a high opening ratio.

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