Fundamental study for high accuracy calculation of 3-D electromagnetic field

The effect of the improper integral and the discretization in 3-D, which are the main error sources in the boundary element method, is investigated. The accuracy of the double numerical integral with a singularity is improved by using the integral variable transform of a double exponential function and executing the integral synchronously along both integral variables. Trigonometric expressions for computation of the integrand are concisely described. Fundamental characteristics of the discretization error in 3-D are demonstrated. The magnitude of the discretization error for the charge distribution can be decreased by combining the piecewise linear solutions with stepwise solutions according to the sizes of the adjacent elements