Electrohydrodynamic and Magnetohydrodynamic Micropumps

A great variety of strategies have been developed to pump fluids in microsystems. According to Laser and Santiago [1] micropumps generally fall into one of two classes: (a) displacement pumps, which exert pressure forces on the working fluid by one or more moving boundaries and (b) dynamic micropumps, which exert forces directly on the liquid, without moving parts. From the latter category, we are going to deal with micropumps that exert electric or magnetic forces on liquids, called electrohydrodynamic (EHD) or magnetohydrodynamic (MHD) micropumps, respectively. The main goal of the present work is to describe the physical principles behind the EHD and MHD micropump actuation, and what physical parameters affect the performance of these micropumps.

The transport of small volumes of liquid in microdevices is often achieved by taking advantage of passive mechanisms such as capillarity or gravity. Sometimes microfluidic applications employ macroscale pumps like syringe pumps or pressure/vacuum chambers and valves. However, many microfluidic applications would benefit from an on-chip active pump with size comparable to the small volume of fluid to be pumped, i.e. an integrated micropump. An integrated pump design that has been studied intensively over the years is the piezo-actuated micropump. In this, a membrane is displaced to create a pulsating flow that is rectified using valves. However, the moving parts make the fabrication and operation delicate. In this context, the requirement of an integrated micropump with no moving parts can be fulfilled by using EHD and MHD micropumps.