April 28, 2006 – Scientists at Purdue U. have developed a MEMS-based micropump small enough to fit on a computer chip that circulates coolant through channels etched directly into the chip.
The technology applies the principle of “electrohydrodynamics,” involving interactions of ions and electric fields to cause fluid to flow. The new device, constructed on a 1x1mm chip, contains numerous 100-micron wide water-filled microchannels, covered with a series of hundreds of electrodes. Varying voltage pulses in the electrodes creates a traveling electric field in the channels, generating ions that are dragged along, and causing the water to flow and induce a cooling action.
“Say every sixth electrode receives the same voltage, these varying voltages from one electrode to the next produce a traveling electrical field that pulls the ions forward, causing the water to flow and inducing a cooling action,” explained Suresh Garimella, prof. of mechanical engineering and director of Purdue’s Cooling Technologies Research Center. “Essentially, you are pumping fluid forward.”
Gluing a thin sheet of piezoelectric material on top of the liquid-filled channels, and applying a voltage to deform it up and down, pushes additional flow through the channels. This “diaphragm” enhances the pumping action by as much as 13%, Garimella noted, but modeling suggests it could boost flow by 100% or more.
Engineers have long utilized electrohydrodynamics to move fluids with electric fields, but the Purdue research marks one of the first times this has been applied at the microscale, Garimella noted. The process generally has been viewed as impractical for pumping applications because it requires too much energy and does not product enough motive force for thrust. However, Garimella noted that this MEMS-based micropump generates milliwatts of cooling for just microwatts of power input — “in other words, the cooling effect is more than a thousand times greater than the energy needed to drive the system. That’s because all we need to do is create enough of a flow to induce cooling.”
Challenges still faced by researchers include sealing the microchannels to prevent water leakage and making the system reproducible using the same conditions as semiconductor chips. Also required are more comprehensive and accurate mathematical models to track the electrohydrodynamic effects, electrical fields, and moving diaphragm.