  We report on an experimental study of a device composed by an array of
submerged, reversed and periodic cylindrical pendula (resonators), whose
objective is the attenuation of surface gravity waves. The idea is inspired by
the concept of metamaterials, i.e. engineered structures designed to interact
with waves and manipulate their propagation properties. The study is performed
in a wave flume where single frequency waves are excited in a wide range of
frequencies. We explore various configurations of the device, measuring the
transmitted, reflected and dissipated energy of the waves. If the incoming wave
frequencies are sufficiently close to the natural frequency of the pendula, we
find a considerable wave attenuation effect, driven by viscous dissipative
mechanisms. This behaviour is enhanced by the number of resonators in the
array. Moreover, the device is also capable of reflecting the energy of
selected frequencies of the incoming waves. These frequencies can be predicted
by assuming the interactions involving at least three wave modes, including
higher harmonics, and are therefore associated with the distance between the
resonators. The presented results show promise for the development of a
environmentally sustainable device for mitigating waves in coastal zones.
