Application Note: Some Potential
To find success in much of the MEMS world, it is necessary to control the motion of small amounts of liquid in micron scale geometry. Thermo-capillarity is one mechanism explored in another article in this Newsletter. Here we consider a potential mechanism called dielectrophoresis, or motion caused by dielectric phenomena.
In the presence of an electric potential the molecules in a dielectric material can be polarized to form a distribution of electrical dipoles. Wherever the electric field is non-uniform its interaction with the dipoles will induce a small body force on the material. Although this is usually an exceedingly small force, on the MEMS scale any force is potentially significant.
One possible application of dielectrophoresis is moving small liquid drops along a channel. If a pair of charged electrodes are placed in the channel near a droplet, it will be induced to move toward the electrode where the electric field has the greatest variation. Thus, by arranging a series of electrodes in the channel and progressively charging and discharging them, one or more droplets may be transported along the channel.
The accompanying figure illustrates a FLOW-3D simulation of the push given an up-and-coming droplet of dielectric liquid by an up-standing electrode exhibiting significant potential. Color in the figure indicates electric potential. The distortion of the leading edge of the droplet signals instability caused by the proximity of the next electrode. Even simple simulations like this one can uncover valuable information.
Charge up FLOW-3D and let it carry you to new levels of understanding. Don’t resist. Its capacity for MEMS applications is truly electrifying.