Improved Version of the Second-Order Mur Absorbing Boundary Condition Based on a Nonstandard Finite Difference Model

It is often necessary to terminate the computational domain of an FDTD calculation with an absorbing boundary condition (ABC). The Perfectly Matched Layer (PML) is an excellent ABC, but it is complicated and costly. Typically at least 8 layers are needed to give satisfactory absorption. Thus in a 100(3) domain less than 84(3) or 59% of the grid points are usable. The second-order Mur ABC requires just 2 layers, but its absorption is inadequate for many problems. In this paper we introduce an improved version of the second-order Mur ABC based on a nonstandard finite difference (NSFD) model which has the same low computational cost but with much better absorption on a coarse grid.