PML Absorbing Boundary
A perfectly matched layer (PML) is an absorbing layer model that — when placed next to an elastic bounded domain — absorbs nearly perfectly all waves traveling outward from the bounded domain, without any reflection from the interface between the bounded domain and the PML.
The outgoing wave is absorbed and attenuated in the PML. There is some reflection of the wave from the fixed outer boundary of the PML, but that reflected wave can be made as small as desired. Therefore, an accurate model of an unbounded domain may be obtained even if the PML is placed very close to the excitation.