Strong attenuation using subwavelength apertures in a phononic plate

International audienceThe aim of this study is to demonstrate an acoustic screening in a periodically perforated plate. The phononic structure is constituted of sub-wavelength slit arrays, of the order of λ/10, in an aluminium plate that is immersed in water. These arrays act as Fabry-Pérot acoustic resonators, and through the coupling effect between them, we obtain a series of asymmetric shape peaks in the transmission spectra. This leads to an enhanced transmission at the res-onance frequencies as well as to improve the attenuation significantly at the anti-resonance frequencies. Therefore, the composition between these anti-resonance frequencies, through the geometrical features, enables to reach an attenuation up to 23 dB, with a relative band-width of 11% and a center frequency of 175 kHz

Opacity and transparency generated by local resonances in acoustic metamaterials

Le domaine des métamatériaux acoustiques connaît un succès grandissant depuis maintenant une vingtaine d’années, notamment en raison de phénomènes exotiques aux perspectives d’applications plus que prometteuses : « l’invisibilité » acoustique en est l’exemple le plus manifeste. Dans cette thèse, nous présentons des métamatériaux acoustiques à résonances locales, et qui permettent de générer aussi bien de l’opacité que de la transparence acoustique. C’est plus particulièrement le couplage entre résonateurs de différentes formes qui est l’objet de nos investigations. Notre étude nous a permis de comprendre que la diffraction est l’une des principales limitation à l’omnidirectionalité des performances d’opacité, que nous avons caractérisé au moyen d’un banc ultrasonore motorisé. Un tel phénomène de diffraction est dû à la présence d’un réseau, et nous proposons dans notre étude des solutions qui permettent de dépasser cette limitation. A partir de cette étude, nous avons ainsi pu transposer au domaine sonore les résultats obtenus pour les ultrasons, ce qui nous a permis de réaliser deux principaux types de dispositifs : des métamatériaux acoustiques aux fonctions de réflecteur d’une part et d’absorbant basses fréquences d’autre part. Enfin, l’étude en homogénéisation de ce type de structure a aussi révélé un effet de densité effective quasi-nulle, dont les applications vont du contrôle de front d’onde, à la furtivité acoustique. De tels résultats offrent un potentiel d’application dans de nombreux champs, que ce soit pour le bâtiment ,l’automobile, l’aéronautique, ou l’acoustique sous-marine.For more than twenty years now, Acoustic Metamaterials are experiencing a growing success, partlydue to exotic phenomena and their wide variety of extremely promising applications: “InvisibilityCloak” is the most vivid example of this. In this thesis, we report on designs of locally resonantacoustic metamaterials, that enable us to generate both sound opacity and transparency. It is moreparticularly 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 omnidirectionalcapabilities involving locally resonant perforated plates, as supported by experimental investigationsrealized 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 theresults obtained in ultrasonic frequencies to the audible range, which permits us to develop twomain kinds of acoustic devices based on metamaterials: broadband reflectors and low-frequencyabsorbers. 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 forpromising applications in various field, including construction, automotive and aeronautical industries,submarine acoustics and so on

Extensive tailorability of sound absorption using acoustic metamaterials

International audienceWe present an experimental demonstration of sound absorption tailorability, using acoustic metamaterials made of resonant cavities that take advantage of the inherent visco-thermal characteristics of air. As confirmed by numerical calculation, we particularly show that using quarter-wave-like resonators made of deep subwavelength slits allows a high confinement of the acoustic energy of an incident wave. This leads to enhance the dissipation in the cavities and, consequently, generates strong sound absorption, even over a wide frequency band. This paves the way for tremendous opportunities in acoustic comfort because of their potentially low density, low volume, broadband, and tailorable capabilitie

Experimental evidence of ultrasonic opacity using the coupling of resonant cavities in a phononic membrane

International audienceWe report the practical realization of phononic membrane with sub-wavelength apertures, inducing a broadband ultrasonic opacity. The ultrasonic experiments confirm the existence of deep and wide attenuation in the transmission spectrum, through periodic aperture arrays in silicon substrate immersed in water. This attenuation reaches 30 dB on a relative bandwidth of 31% with a center frequency of 0.9 MHz. The arrays act as Fabry-Perot acoustic resonators, and through the coupling effect between them, we obtain a series of asymmetric shape peaks in the transmission spectra. This leads to an enhanced transmission at the resonance frequencies as well as to improve the attenuation significantly at the antiresonance frequencies

Low frequency sound screening using an acoustic metamaterial made of space-coiled resonant cavities

International audience<font face="null"&gt<span style="font-size: 13px;"&gtLow frequency sound screening using an acoustic metamaterial made of space-coiled resonant cavities</span&gt</font&g