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Transformation acoustics opens a new avenue towards the architecture, modeling and simulation of a new class of sonic composites with scatterers made of various materials and having various shapes embedded in an epoxy matrix. The design of acoustic scatterers is based on the property of Helmholtz equations to be invariant under a coordinate transformation, i.e., a specific spatial compression is equivalent to a new material in a new space. In this paper, the noise suppression for a wide full band-gap of frequencies is discussed for spherical shell scatterers made of auxetic materials (materials with negative Poisson's ratio). The original domain consists of spheres made from conventional foams with positive Poisson's ratio. The spatial compression is controlled by the coordinate transformation, and leads to an equivalent domain filled with an auxetic material. The coordinate transformation is strongly supported by the manufacturing of auxetics which is based on the pore size reduction through radial compression molds. [ABSTRACT FROM AUTHOR]

The sound attenuation in a sonic composite without/with point defects is studied using a new method that combines the features of the cnoidal method and the genetic algorithm. Acoustic scatterers are composed by piezoceramic hollow spheres of functionally graded materials-the Reddy and cosine graded hollow spheres. This method enables to obtain the dispersion relation for defect modes, and the prediction of the evanescent nature of the modes inside the band-gaps. [ABSTRACT FROM AUTHOR]