In search of the perfect absorber as an internal and external ABC

A perfect absorber (PA) is seen as equivalent to an ideal antenna (IA), except that it absorbs the power from any angle of incidence. Similarly to the IA, the absorbed power is maximal for all substances supported by the same physical structure. When defining the PA in this way, care should be taken to avoid the superdirective zone. This is done by using the constraint Q = 1 for the quality factor around the absorber. Possible applications for numerical simulations are outlined.