Perfect absorption using sparse arrays of Helmholtz resonators

We inspect the influence of the spacing on the resonance of a periodic arrangement of Helmholtz resonators for which an effective model is derived. It is shown that the strength of the resonance is enhanced when the array becomes sparser, which provides a degree of freedom to control the radiative damping of the array. This is of particular interest since it does not affect the resonance frequency nor the damping due to losses within each resonator; besides, it does not affect the total thickness of the array. We show that it can be used for the design of a perfect absorbing walls.