Applied Physics

Circuit Training for Fluids

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Science  20 Mar 2009:
Vol. 323, Issue 5921, pp. 1539
DOI: 10.1126/science.323.5921.1539c

A nagging problem in microfluidic reactor design is the need for bulky external apparatus to control the pumping and directing of the fluid flows. To circumvent this issue, Leslie et al. tried to mimic passive electrical circuits—resistors, capacitors, and diodes. Capacitors store electrical charge, a function mimicked by bonding a deformable elastomeric film to a fluid microchannel, so that the film bulged to allow more fluid storage as the overall pressure increased. Diodes, which permit flow in only one direction, were fabricated by bonding a deformable film on top of a weir, thus allowing flow only when the pressure was above a critical value. Through a combination of these circuit elements, fluid flow could be predicted and controlled by modulating a pressure source with time through a selection of resistive channels and capacitors. More complex flows were achieved by creating branched streams that merged at the output channel. The flow from each branch was regulated by the frequency of the pressure oscillations, effectively rendering the device a bandpass filter. Diodes, with their nonlinear response to pressure, were used to convert oscillatory flow to steady flow, similar to the conversion of electrical current from ac to dc. — MSL

Nat. Phys. 5, 231 (2009).

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