Analysis of a charge probe and its response near metallic and dielectric interface

An electrically short thin-wire antenna oriented normal to a conducting surface is often used to measure the normal electric field or charge density at the surface. Calibration of the so-called charge probe is relatively simple if there are no nearby objects which can "load" the probe and alter its response. A probe on a surface near a dielectric or conducting interface is a case of practical interest in which probe loading must be accounted for if accurate measurements are expected. The main purposes of this paper are to lay the groundwork for an understanding of probe loading and to suggest a simple method for accounting for the effects of loading as the charge probe becomes arbitrarily close to the interface. We present a simple and accurate method for determining the current in a short wire very near to an interface. Data computed from a method employing Sommerfeld integrals and the proposed approximate method are compared.