Sonic crystal noise barriers made of resonant elements

The main spectral property of a Sonic Crystal structure is a notable sound attenuation related to the Bragg band gaps. This effect is observed in air and makes Sonic Crystals effective noise barriers in a particular frequency range. This performance can be extended to a wider range of frequencies by introducing scatterers supporting multiple resonances of various types. In this paper the sonic crystals composed of infinitely long multi-resonant composite scatterers are studied. First the concentric elastic shell and outer 4-slit rigid cylinder composite is considered. Theoretical and experimental results show the existence of the axisymmetric resonance of the elastic shell followed by the annular cavity resonance. The second type of scatterers considered is a U-shaped resonator composed of thin elastic plates. The plates form an open cavity so that resonances are defined by their bending motion as well as by the geometry of the scatterer. Theoretical analysis of the elastic-acoustic coupling in a single scatterer is based on the Kirchhoff-Love asymptotic theory. Numerical results on the overall performance of the proposed structures are obtained with the multiple scattering technique and finite element method. The predictions are compared with the experimental results.