Improved 3D boundary charge method for high-accuracy calculation of potential and electric field in composite dielectric system

In this paper we propose an improved three-dimensional (3-D) boundary charge method (BCM) for a composite dielectric system in which insulators, i.e., dielectric materials exist together with conducting electrodes. The method is based on the idea that the composite dielectric system can equivalently be replaced with a conductor system in vacuum by introducing an apparent surface charge density (= true surface charge density + polarization surface charge density), on every conductor-to-dielectric interface and every dielectric-to-dielectric interface. In calculating the apparent surface charge density, whole interfaces are divided into n small surface elements, and the apparent surface (or boundary) charge density on each small surface element is obtained by solving a set of n-dimensional simultaneous linear equations, where the coefficient matrix element is expressed as a double integral and the diagonal matrix element becomes a singular or nearly singular integral. A high-accuracy and high-speed calculation of the double integral is the key point of the method, and we have succeeded in great improvement of both numerical accuracy and computation time.