Aliyasin El Ayouch defended his PhD thesis on December 3, 2015

Locally-resonant opacity and transparency in acoustic metamaterials

For more than twenty years now, Acoustic Metamaterials are experiencing a growing success, partly due to exotic phenomena and their wide variety of extremely promising applications: “Invisibility Cloak” is the most vivid example of this. In this thesis, we report on designs of locally resonant acoustic metamaterials, which enable us to generate both sound opacity and transparency. It is more particularly coupling between resonators having different forms which is the focus of our work. This study permit us to understand that diffraction is one of the main limitation of omnidirectional capabilities involving locally resonant perforated plates, as supported by experimental investigations realized using a motorized ultrasonic set-up. We proposed solutions to overcome such a limitation, in the case where the opacity mechanism uses diffraction gratings. From this, we transposed the results obtained in ultrasonic frequencies to the audible range, which permits us to develop two main kinds of acoustic devices based on metamaterials: broadband reflectors and low-frequency absorbers. Finally, homogenization study of such structures revealed an effect of density near-zero, with applications from shaping wave front, to acoustic furtiveness. Such results paves the way for promising applications in various field, including construction, automotive and aeronautical industries, submarine acoustics and so on.