MEMS World - Electrostatics

From the single charge to Dielectrophoresis

This section is dedicated to the understanding of electrostatics and dielectrophoresis, that are must-know for MEMS workers. It can be seperated in two parts:

These two phenomenons are used in very different cases, but they both rely on electric fields and charges. So I've decided to include them in the same section!

The mathematical equations are written in MathML. I strongly recommand you to use a compliant browser or to install a proper plugin.

Electromagnetic knowledge is more than two centuries old. Still, it has brought us mobile telecommunication and there are a lot of other useful applications coming directly from electrostatics. The first used in MEMS are electrostatic actuators, another one of them is dielectrophoresis.
Dielectrophoresis has been discovered at then end of the 70's. One of its main modern application concerns biological micro-objects manipulation, such as biocells, D.N.A. molecules, etc. It is by the way easier to fabricate a working dielectrophoretic system than an actuator doing the same task. And the dielectrophoretic system has the advantage of longer lifetime because there is no mechanical actuation.

Electrostatic actuation

Electrostatic actuation is the first application of electrostatics people think about when talking about MEMS. It is a very basic direct use of electric field between two conductive objects and is widely used.
You can find further information about MEMS electrostatic actuator in the MEMS - Electrostatic page.
Here you can find a calculation of what could be a electrostatically tunable MEMS capacitor:

Electrostatic force and actuation calculation

Electrostatic actuation was used in a device I've made during my PhD: the micro-extractor.

Dielectrophoresis Summary

Dielectrophoresis is a major tool in modern microfluidics. It allows the manipulation and sorting of dielectric micro-object in liquid quite easily. The main applications concerns biocells and D.N.A. molecules.
Dielectrophoresis was used in the micro-extractor I've made during my PhD.
Here you can find mathematical resources for the calculation of the dielectrophoretic force:

  1. About charge and polarization
  2. Dielectric sphere in an electric field
  3. Dielectrophoresis