Unsplit Implementation of Higher Order PMLs

An unsplit implementation of higher order perfectly matched layers (PMLs) using a recursive integration approach is presented. The formulation, which is based on the complex coordinate stretching of space, is developed for a general complex frequency-shifted stretching function but is applicable to PMLs employing the standard stretching function or a mixture of either types. The approach results in the development of two general formulae that could be used to easily generate PML correction equations for any PML order. Numerical results from finite-difference time-domain models are presented to illustrate the validity of the approach.