  The effect of the presence of a finite impedance surface on the wave
propagation properties of a two-dimensional periodic array of rigid cylinders
with their axes perpendicular to the surface is both numerically and
experimentally analyzed in this work. In this realistic situation both the
incident and the scattered waves interact with these two elements, the surface
and the array. The interaction between the excess attenuation effect, due to
the destructive interference produced by the superposition of the incident wave
and the reflected one by the surface, and the bandgap, due to the periodicity
of the array, is fundamental for the design of devices to control the
transmission of waves based on periodic arrays. The most obvious application is
perhaps the design of Sonic Crystals Noise Barriers. Two different finite
impedance surfaces have been analyzed in the work in order to observe the
dependence of the wave propagation properties on the impedance of the surface.
