  We investigate the impact of resonator geometry and its coupling with ground
plane on the performance of metamaterial perfect absorbers. Using a
cross-resonator as an example structure, we find that the absorber thickness
can be further reduced through modifying the geometric dimensions of the
resonators. Numerical simulations and theoretical calculations reveal that
destructive interference of multiple reflections is responsible for the
near-unity absorption. The near-field coupling between the resonator array and
ground plane can be significant. When this coupling is taken into account, the
theoretical results calculated using the interference model are in excellent
agreement with experiments and numerical simulations.
