Finite-Element Simulations of the Effects of Shielding and Guarding of a Capacitor Using Coaxial Cylindrical Electrodes for Electrostatic Force Balance Measurements

This work reports investigations of the possible effects of shielding and guarding of a capacitor using coaxial cylindrical electrodes on the capacitance gradient determination in electrostatic force balance measurements. The capacitances of capacitors using coaxial cylindrical electrodes were calculated by the finite-element method (FEM) in a condition that the shielding/guarding electrode of the capacitor is open or semi-closed using a metal lid on the shielding electrode. The results showed that the residuals from the linear fit in the capacitance gradient determination in the open-shielding case attained almost identical values to those in the semi-closed-shielding case, which was confirmed by experiments using a voltage balance apparatus. The FEM results also suggested that the grounding of the capacitor can have a considerable impact on the mass and force determination using the electrostatic force based on the capacitance measurements.