Characterization of an electrodynamic balance for suspending charged droplets

The electrical characteristics of an electrodynamic balance used for suspending charged droplets were determined by constructing a computer model based on the charge simulation technique. This device is traditionally constructed with hyperbolically shaped endcaps and ring electrodes since an analytical solution exists for the electric field in this geometry. Using the charge simulation technique, other electrode shapes (some with observation portals) were evaluated for their effectiveness in suspending and stabilizing droplets. In this stability study, the motion of a droplet within the electrodynamic balance was evaluated using a numerical solution of the equations of motion for a droplet in the calculated electrodynamic force field. Four shape attributes were considered: electrode curvature; chamber size and geometry; and electrode extension. Three end cap curvatures were examined: flat, hyperbolic, and more steeply curved. Two principal findings are: (1) viewing ports should be embedded within an axially symmetric groove, in which case they do not affect the function of the balance; and (2) the voltage needed to balance a particle against gravity is a strong function of the chamber geometry