Electromechanical effects on multilayered cells in nonuniform rotating fields.

We use the Maxwell stress tensor to calculate the dielectrophoretic force and electrorotational torque acting on a realistic four-shelled model of the yeast Saccharomyces cerevisiae in a nonuniform rotating electric field generated by four coplanar square electrodes. The comparison of these results with numerical calculations of the dipolar and quadrupolar contributions obtained from an integral equation for the polarization charge density shows the effect of the quadrupole contribution in the proximity of the electrode plane. We also show that under typical experimental conditions the substitution of the multilayered cell by an equivalent cell with homogeneous permittivity underestimates the quadrupole contribution to the force and torque by 1 order of magnitude.