Ac electrokinetics: a survey of sub-micrometre particle dynamics

Particles suspended in fluid exhibit motion when subjected to ac electric fields. The applied field results in forces on both the particles and the fluid, the study of which is referred to as ac electrokinetics. The ac electrokinetic techniques can be used for the controlled manipulation and characterization of particles, and the separation of mixtures. For sub-micrometre particles, Brownian motion is important and strong electric fields are required to overcome these effects. Planar micro-electrode arrays, fabricated using semiconductor manufacturing processes, can generate electric fields of the required strength from low potentials over a wide range of frequencies. This paper reviews and discusses sub-micrometre particle dynamics under the influence of dielectrophoretic and electrohydrodynamic forces. New experimental observations of the movement of sub-micrometre particles are also presented. (Some figures in this article appear in colour in the electronic version; see www.iop.org)