Planar quadrupole microelectrodes, fabricated using surface micromachining,
have been successfully used to achieve passive levitation of biological ce
lls and other microscopic inorganic particles. To explain certain experimen
tal findings, namely the "size effect", a simple point charge quadrupole mo
del was invoked to explain qualitatively the experimental observations. Sub
sequently, a more generalized multipolar theory was formulated to handle su
ch higher-order multipolar effects. In this paper, we examine the salient p
roperties 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 si
mulation 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 pre
dictions of multipolar theory. (C) 1999 Elsevier Science B.V. All rights re
served.