We introduce an approach blending the Perfectly Matched Layer (PML) and infinite element paradigms, to achieve better performance and wider applicability than either approach alone. In this paper, we address the specific challenges of unbounded problems when using time-domain explicit finite elements:
1. The algorithm must be spatially local, to minimize storage and communication cost,
2. It must contain second-order time derivatives for compatibility with the explicit central-difference time integration scheme,
3. Its coefficient for the second-order derivatives must be diagonal (“lumped mass”),
4. It must be time-stable when used with central-differences,
5. It must converge to the correct low-frequency (Laplacian) limit,
6. It should exhibit high accuracy across typically encountered dynamic frequencies, i.e. at short to long wavelengths,
7. Its user interface should be as simple as possible.
Here, we will describe the derivation of a time-domain implementation of the hybrid PML/infinite element, and discuss its advantages for implementation.