4. Conclusion

The field of phononic crystals and metamaterials has reached critical mass and conceptual maturity. The exploration of the physics associated with these artificial materials has proved very rich. Beyond the phenomena presented, other academic research is being carried out on topological acoustic insulators, on the influence of deliberately introduced disorder, on nonlinear phenomena and dissipation, and on non-reciprocal systems. Eventually, this state of affairs will make it possible to seriously consider the concrete implementation of certain concepts, with the aim of achieving realizations designed to meet industrial challenges. The first step is to better understand the link between the structure of the artificial material and its functional performance (absorption, wave reflection, etc.), in order to meet specific needs.

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