Optimizing the electrode shape for fourelectrode electrorotation chips.
Electrorotation experiments are conducted in harmonic rotating fields to characterize the passive electric properties of cells 01″ particles by their frequency-dependent rotation speed. The torque of the objects is proportional to the square of the field strength. Therefore, a rotating field of constant amplitude is desirable over a large area of the measuring chamber for reproducible measurements. In this study the field distribution in chip chambers was analyzed using numerical field simulation in combination with analytical post-processing. The electric field distribution was compared for various electrode shapes. For the center, correction factors could be calculated, relating the actual field strength to the quotient of electrode voltage and distance. Apart from the center, the field was elliptically polarized with an eccentricity increasing with the distance from the center. A spherical model object has been assumed to derive a theoretical expression for the torque induced by an elliptical field. This model allowed us to consider the torque deviation for each site with respect to the torque induced by the circular center-field. Various electrode shapes have been checked for minimum deviations of the torque. We found the optimal chip design for electrorotation to feature electrodes with round tips.