A cyclic particle extractor based on particle diffusion is presented. The extraction realized by the device features simplicity, programmability, and low cost. Although conventional particle separation based on diffusion can be spontaneously realized without any active inputs, the extraction efficiency decreases as the size difference between particles decreases or if the diffusion length is insufficient. In this article, a primary extraction procedure including four operational steps is proposed to facilitate the process. By simply repeating the procedure, the separation scheme is additive, and increased efficiency is observed with each additional cycle. A mixture of 0.5- and 3-μm polystyrene particles was separated in up to 10 extraction cycles. Using a 2.5-Hz phase frequency, the average flow velocity was 2.5 mm/s. An unequal volume ratio of the sample stream to extraction stream (45:55) created a barrier region to help minimize unwanted (large) particles from entering the extraction stream. The initial concentration of the extracted small particles was 7.5% after 2 cycles, but jumped up to 38% after 10 cycles.
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