View source for Tuned-in flow control

Original Entry by Che-Hang Yu, AP225 Fall 2009

== Overview ==

Title: [http://www.nature.com.ezp-prod1.hul.harvard.edu/nphys/journal/v5/n3/full/nphys1213.html Microfluidics: Tuned-in flow control]

Author: Howard A. Stone

Journal: Nature Physics 5, 178 - 179 (2009)

Subject Categories: Fluid dynamics; Electronics, photonics and device physics

[[Image:H291_Fig1.jpg||thumb||300px||Figure 1: Demonstration of the approach. Construct two flow channels with two sets of microfluidic resistors, capacitors and diodess, and finally feed into a single output in the end. Both channels are driven by a single oscillatory source. Changing the frequency of the source switches the flow of liquid to the output from one channel to another.]]

== Summary ==
Designing microfluidic channels based on the analogical concept to the electrical circuit is presented and demonstrated by Lesile et al. in this paper. This approach can selectively control the flow of multiple fluids with different oscillating pressure. This method also can help reduce the amount of equipments to operate a microfluidic systems, and therefore improve their portability and widen their applicability. 

Taking the advantage of the elastic response of certain soft materials, Lesile et al. successfully introduce multiple elememts in series to build the frequency-dependent microfluidic circuit. This approach is inspired by the electrical circuit theory. For example, when a resistance, R, is jointed with a capacitance, C, their combined response is frequency-dependent, and their characteristic frequency is 1/(RC). Besides, a analogical concept from a diode is used to provide a d.c. component to a.c. forcing. The microfluidic analogue of resistance comes from the viscous resistance of the flow channel and also from the viscosity of fluid. The fluid equivalent of capacitance results from the expansion and contraction of the elastic reservoirs, like a water balloon to hold varying amounts of liquid. Lesile et al. also introduce the pressure-sensitive valve as a microfluidic equivalent of diode to provide a net flow. Figure 1 illustrates the demonstration of this concept.

The author suggests to construct more flow channels controlled based on this concept, and even scale up into three-dimensional networks. Alternatively, it might integrate CMOS technologies with microfluidic networks to actively manipulate the characteristic frequency of microfluidic circuit through the manipulation of the elastic materials by changing the embedded electrical or magnetic fields.