When using the moment method to solve three-dimensional electromagnetic problems with subsectional sinusoid expansion functions and Galerkin's method, an integral in the form of a sinusoid and exponential is often encountered. Since this integral is typically evaluated many times in the course of solving a problem, efficient numerical evaluation of the core integral could lead to a significant reduction of computation time. A new computing algorithm based upon series representation of the integrand is presented which can quickly evaluate this expression. Typical execution time comparisons on several computers are given. © 1990 IEEE