The perfectly matched layer as a synthetic material with active inclusions

The perfectly matched layer is a successful concept used in finite difference numerical techniques. It can be also considered as a uniaxial medium whose tensor material parameters are subject to certain requirements. Here we demonstrate that such a medium is in principle physically realizable as a composite material with small inclusions, but the inclusions must be active, which means that they can only be realized as active electronic circuits, e.g., circuits based on operational amplifiers.