  The impedance matching in metamaterial perfect absorbers has been believed to
involve and rely on magnetic resonant response, with a direct evidence from the
anti-parallel directions of surface currents in the metal structures. Here we
present a different theoretical interpretation based on interferences, which
shows that the two layers of metal structure in metamaterial absorbers are
linked only by multiple reflections with negligible near-field interactions or
magnetic resonances. This is further supported by the out-of-phase surface
currents derived at the interfaces of resonator array and ground plane through
multiple reflections and superpositions. The theory developed here explains all
features observed in narrowband metamaterial absorbers and therefore provides a
profound understanding of the underlying physics.
