Improved implementation of the Mur first-order absorbing boundary condition in the ADI-FDTD method

Current implementations of the Mur 1st-order absorbing boundary condition (Mur1) in the alternating-direction implicit finite-difference time-domain (ADI-FDTD) method treat the intermediate (half-step) variables as electromagnetic field quantities that are an approximate solution to Maxwell's equations. This approach is problematic because these variables represent nonphysical quantities. Here, we rederive the Mur1 boundary condition for both the one-dimensional and three-dimensional cases such that the intermediate (half step) values are updated at a manner that is consistent with the ADI-FDTD scheme. We present numerical tests that show improved performance over existing Mur(-1) implementations in ADI-FDTD. These results.suggest that careful consideration of the derivation of the half-step variable update equations for other special ADI-FDTD boundary and material conditions may yield similar improvements. (C) 2008 Wiley Periodicals, In