NONUNIFORM SPATIAL DISTRIBUTIONS OF BOTH THE MAGNITUDE AND PHASE OF AC ELECTRIC-FIELDS DETERMINE DIELECTROPHORETIC FORCES

It is well known that the conventional dielectrophoretic force acting on a polarised particle in a non-uniform AC electric field is proporti onal to the in-phase component of the induced dipole moment and the no n-uniformity of the field strength. In contrast, the travelling-wave-d ielectrophoretic force that acts on a particle subjected to a travelli ng electric field is proportional to the out-of-phase component of the induced dipole moment. We derive a theory that unifies the descriptio n and interpretation of conventional dielectrophoretic and travelling- wave-dielectrophoretic forces. We show that a particle in a non-unifor m AC electric field experiences a dielectrophoretic force due to spati al non-uniformities of the magnitude and the phase of the field intera cting, respectively, with the in-phase and out-of-phase components of the induced dipole moment. The theory is used to explain the translati onal effects observed for particles in the presence of standing, trave lling and rotating fields in several experimental electrode configurat ions. The good agreement found between the experimental observations a nd the theoretical predictions validate the theory.