Quadrupole levitation of microscopic dielectric particles

Planar quadrupole microelectrodes, fabricated using surface micromachining, have been successfully used to achieve passive levitation of biological cells and other microscopic inorganic particles. To explain certain experimental findings, namely the "size effect", a simple point charge quadrupole model was invoked to explain qualitatively the experimental observations. Subsequently, a more generalized multipolar theory was formulated to handle such higher-order multipolar effects. In this paper, we examine the salient properties of a practical planar quadrupole electrode structure as predicted by multipolar theory. The analytical data, obtained from multipolar theory is compared with the numerical modeling results form a boundary element simulation package and the levitation data of microscopic Spheriglass(R) and polymethylmethacrylate particles. The numerical simulation results and the levitation data are both consistent with and in good agreement with the predictions of multipolar theory. (C) 1999 Elsevier Science B.V. All rights reserved.