LMA - Laboratoire de Mécanique et d’Acoustique

H. Lissek - Electroacoustic Metamaterials : towards effective sound waves manipulation in the subwavelength regime

Amphithéâtre François Canac, LMA

Le 11 juin 2019 de 10h00 à 11h00

Hervé Lissek
Laboratoire de Traitement des Signaux LTS2, EPFL

Acoustic metamaterials / metasurfaces have raised a growing interest in the scientific community during the last decade, exhibiting a wide range of fancy acoustic properties (negative refraction, anomalous reflection/transmission, acoustic prism, orbital angular momentum), and since very recently, promising applications (acoustic leaky wave antenna, superlensing, cloaking). One of the specificity of such “meta-“ concept is that the size of the elementary elements constituting these structures is much smaller than the working wavelength, attracting the interest for developing soundproofing materials for the (audible) low-frequency regime (few tens of Hertz, corresponding to wavelengths of the order of 1 – 10 m !). However, most if not all of the metamaterial structures reported so far fail to show applicable properties, mainly due to the fact that the proposed concepts rely on passive structures, which are inherently resonant and lossy, therefore effective only over very limited frequency bandwidths if not effective at all.

The development of active acoustic impedance control techniques may be a serious candidate to overcome such limitation. In this talk, we will present the specific concept developed at EPFL in the last 10 years, allowing turning a conventional loudspeaker into a broadband Active Electroacoustic Resonator (AER) with adjustable acoustic properties, that can be easily tuned on-the-fly. Several applications of the concepts have been successfully assessed so far, such as low-frequency room modes damping (this work has led to the only commercial product available on the market, AVAA C20 by PSI Audio), or Tunable Acoustic Lining for aircraft engines nacelles. New routes are now envisaged towards the application of AER to metasurfaces, in a view to achieving controllable and broadband sound wave redirection (reflection/transmission), with potential applications to room acoustics and noise control engineering.

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