Nonlinear acoustic waves in periodic media (original) (raw)

A high amplitude acoustic wave travelling in a fluid develops higher harmonics as it propagates through the medium. In a homogeneous fluid, such nonlinearly generated harmonics grow during propagation because of the lack of dispersion. On the other hand, periodic acoustic media such as 1D layered media, or 2D sonic crystals, are known to introduce strong dispersion in wave propagation, even creating forbidden propagation bands or bandgaps where wave propagation at particular frequencies is not allowed. The combined action of nonlinearity (harmonic generation) and periodicity (different propagation velocities and attenuation for the different harmonics) results in novel and unexpected phenomena with respect to the linear counterpart, and opens the door to new mechanisms of acoustic wave control and manipulation. Here we investigate numerically the propagation of a plane acoustic wave in a periodic medium in two situations: a structured fluid, formed by a periodic array of fluid layers with alternating acoustic properties, and a 2D squared array of solid scatterers embedded in a fluid (a sonic crystal). We show how the nonlinear generation and propagation of the second harmonic is strongly affected by the presence of the crystal. PACS no. xx.xx.Nn, xx.xx.Nn

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