HOW TO DESIGN THE IMPERFECT BERENGER PML

In contrast to the previously popular second order Mur absorbing bound ary condition (ABC), the recently introduced Berenger Perfectly Matche d Layer (PML) ABC can be designed to lower the numerical reflection co efficient associated with mesh truncation by several orders in magnitu de. Nonetheless the PML ABC is not perfect; it does have a numerical r eflection coefficient. This reflection coefficient is characterized in the time and frequency domains for narrow and broad bandwidth pulses from several points of view including specifically its behavior in ter ms of the magnitude of the loss tangent in the PML and the thickness o f the PML. It is demonstrated that for broad bandwidth pulses the PML ABC exhibits a low frequency increase in its reflection coefficient th at is associated with the actual thickness of the PML layer in terms o f the longest wavelengths contained in the signal incident upon it. Mo reover, it is shown that the effectiveness of the PML ABC saturates wh en the loss parameters of the PML are significantly increased and that this behavior is connected with the size of the first discontinuity i n the material properties encountered by a pulse as it propagates into the PML region. An optimal operating point for the design of the PML region is thus obtained.