VALIDATION OF SHIFT CELL APPROACH FOR THE MODELLING OF ACOUSTIC PROPERTIES OF POROUS MATERIALS EMBEDDING PERIODIC INCLUSIONS

International audienceThe design based on periodic elements can be a powerful strategy for the achievement of lightweight sound packages and can represent a useful solution for manufacturing aspects. The inclusion of vibroacoustic design rules, at early stage of the product development, is a feasible and interesting research target; in fact, the use of porous media with periodic inclusions can improve the dynamic filtering effects thus offering several possibilities of applications in the engineering fields where both weight and space, as well as vibroacoustic integrity and comfort, still represent critical issues. Indeed, although porous materials are commonly used for vibroacoustic applications, they suffer from a lack of absorption at low frequencies. This difficulty is usually overcome by a multi-layering approach. However, while reducing the impedance mismatch at the air-material interface, the efficiency of such devices relies on the allowable thickness. A more efficient way to enhance the low frequency performances of sound packages consists in embedding periodic inclusions in a porous layer. If the radius of these periodic inclusions is comparable with the acoustic wavelength, then an increase of the acoustical performances can be observed since the excitation of additional acoustic modes helps in dissipating more acoustic energy. Therefore, even if this procedure still relies on the dimension of the inclusions, it can provide an acoustical performance improvement, which is way more efficient than just increasing the thickness. This paper starts with the description of the shift cell technique, which allows the description of the propagation of all existing wave