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Two types of air-saturated porous materials are employed to study and validate all the derived sum rules for a single-layer material.

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International audience; We started in September 2019 a new master curriculum at Le Mans University, as part of a plan of actions in the frame of the Institut d?Acoustique - Graduate School. This Institute is related to a project funded by the French state, launched in 2018 in the frame of the national call ?Ecole Universitaire de Recherche? and which intends to offer ?Universities the possibility to reinforce the international impact and attractiveness of their research and training activities in one or several scientific domains, by integrating master and doctoral trainings with high level laboratories? and to introduce in France the model of Graduate Schools. One proposed action to implement all this, was to launch a new master curriculum focused on training by and through research, rethinking usual ways of organizing the training at master level in France, and inspired from several US and European universities. In this presentation, we will describe this new master curriculum on Wave Physics & Acoustics and in particular how we implemented a plan to favor education by and through research. We will highlight the necessary adjustments we had to make and the expected outputs for the students and the laboratory.

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[EN] We report a theoretical and experimental study of an array of Helmholtz resonators optimized to achieve both efficient sound absorption and diffusion. The analysis starts with a simplified 1D model where the plane wave approximation is used to design an array of resonators showing perfect absorption for a targeted range of frequencies. The absorption is optimized by tuning the geometry of the resonators, i.e., by tuning the viscothermal losses of each element. Experiments with the 1D array were performed in an impedance tube. The designed system is extended to 2D by periodically replicating the 1D array. The 2D system has been numerically modeled and experimentally tested in an anechoic chamber. It preserves the absorption properties of the 1D system and introduces efficient diffusion at higher frequencies due to the joint effect of resonances and multiple scattering inside the discrete 2D structure. The combined effect of sound absorption at low frequencies and sound diffusion at higher frequencies, may play a relevant role in the design of noise reduction systems for different applications., This research was funded by the European Space Agency under the Networking/Partnering Initiative (NPI) contract number 441-2015. In memoriam to Julián Santiago-Prowald, Senior Advisor for the Structures, Mechanisms and Materials Division of ESA, a great man that always gave us his tireless support. AC acknowledges financial support from Generalitat Valenciana through the grant APOSTD/2018/229. VRG acknowledges the financial support from RFI Le Mans Acoustique (Région Pays de la Loire) in the framework of the project HYPERMETA funded under the program Étoiles Montantes of the Région Pays de la Loire. Authors acknowledge the support of the European Space Agency under contract 441-2015 Co- Sponsored PhD ¿Acoustic Reduction Methods for the Launch Pad¿ and project TRP ESA AO/1-9479/18/NL/LvH ¿Launch Sound Level Reduction¿. This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology).

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International audience; A low mass and space requirement structure exhibiting high sound insulation over a wide frequency range is a major industrial concern, especially in the transport and building sectors. Metaporoelastic layer is promising structured interface to solve this issue. It consists of a poroelastic layer with periodic resonant inclusions embedded in [1]. The acoustic properties of such metaporoelastic interfaces are greatly enhanced in the low frequency range compared to those of the single poroelastic layer. The studied interface is a metaporoelastic layer covered with an impermeable film on one side and by an elastic plate on the other side. Experimental evidence of a huge improvement in the transmission loss of this structure compared to the same structure in the absence of resonant inclusion is reported. This work aims at understanding the physical phenomena at the origin of this improvement. A finite element model under Comsol Multiphysics is proposed to obtain the transmission loss of such kind of systems and validated against Multiple Scattering results. The acoustic behavior of the structure is investigated via a systemic study of configuration of increasing complexity: from an infinite poroelastic layer to a coated metaporoelastic layer backed by the elastic plate. The physical contributions of each element to the extraordinary transmission loss are thus identified. [1] T. Weisser, J.-P. Groby, O. Dazel, F. Gautier, E. Deckers, S. Futatsugi and L. Monteiro, Acoustic behavior of a rigidly backed poroelastic layer with periodic resonant inclusions by a multiple scattering approach, J. Acoust. Soc. Am., 139: 617-630, 2016.

[FR] Dans ce travail, nous montrons les possibilités des métamatériaux acoustiques pour la conception de matériaux structurés sublongueur d'onde dans les cas de l¿absorption parfaite et la diffusion du son. Basé sur les concepts des ondes lentes et du couplage critique, nous concevons des blocs résonants qui peuvent être assemblés et ainsi réaliser des traitements pour l'absorption et la diffusion avec des performances équivalentes ou supérieures aux traitements acoustiques habituels. L'absorption parfaite est abordée à la fois dans les problèmes de réflexion pure et de transmission, deux problèmes de complexité croissante. Les diffuseurs ainsi que les absorbeurs parfaits sublongueur d'onde sont comparés aux traitements traditionnels, ce qui montre une nouvelle façon de concevoir des traitements acoustiques avec des propriétés accordables., [EN] In this work, we show the possibilities of acoustic metamaterials for designing subwavelength structured materials for perfect sound absorption and diffusion. Based on the concepts of slow waves and critical coupling, we design resonant building blocks that can be assembled to create deep subwavelength acoustic treatments for sound absorption and diffusion with performances equivalent or superior to the usual acoustic treatments. Perfect absorption is addressed in both pure reflection and transmission, two problems of increasing complexity. Diffusers as well as perfect absorbers, both with subwavelength dimensions, are compared to traditional treatments, showing a new way of designing acoustic treatments with tunable properties.

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[EN] In this work we report a mechanisms providing symmetric perfect acoustic absorption by sub-wavelength structures in the ventilation problem. While in the problem of reflection the mechanism consists in critically coupling a single resonance independently of its nature, the problem of transmission becomes more complicated and a degenerate resonator with symmetric and antisymmetric resonances should be designed with both resonances critically coupled. The system analyzed in this work is made by a panel with a periodic distribution of slits, the upper wall of which are loaded by Helmholtz Resonators. The propagation in the slit is highly dispersive due to the presence of the resonators, producing a slow sound propagation before the resonance, and down shifting it to low frequencies. By controlling the geometry of the resonator, the visco-thermal losses can be tuned in order to compensate the leakage of the system and fulfill the critical coupling condition so activating the perfect absorption of sound. In the case of transmission, a double slit is needed, one acting as symmetric and the other one as antisymmetric resonators., The authors gratefully acknowledge the ANR-RGC META- Room (ANR-18-CE08-0021) project and the project HYPERMETA funded under the program E?toiles Montantes of the Région Pays de la Loire. This article is based upon work from COST (European Cooperation in Science and Technology) Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology).

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International audience; In the last few decades, metamaterials have revolutionized the ways in which waves are controlled, and applied in physics and practical situations. The extraordinary properties of metamaterials, such as their locally resonant structure with deep subwavelength band gaps and their ranges of frequency where propagation is impossible, have opened the way to a host of applications that were previously unavailable. Acoustic metamaterials have been able to replace traditional treatments in several sectors, due to their better performance in targeted and tunable frequency ranges with strongly reduced dimensions.This is a training book composed of nine chapters written by experts in the field, giving a broad overview of acoustic metamaterials and their uses. The book is divided into three parts, covering the state-of-the-art, the fundamentals and the real-life applications of acoustic metamaterials.

International audience; In the last few decades, metamaterials have revolutionized the ways in which waves are controlled, and applied in physics and practical situations. The extraordinary properties of metamaterials, such as their locally resonant structure with deep subwavelength band gaps and their ranges of frequency where propagation is impossible, have opened the way to a host of applications that were previously unavailable. Acoustic metamaterials have been able to replace traditional treatments in several sectors, due to their better performance in targeted and tunable frequency ranges with strongly reduced dimensions.This is a training book composed of nine chapters written by experts in the field, giving a broad overview of acoustic metamaterials and their uses. The book is divided into three parts, covering the state-of-the-art, the fundamentals and the real-life applications of acoustic metamaterials.

[EN] Matrices are introduced in mathematical subjects in connection with vector spaces and linear algebra, being disconnected from their applications in other fields of science and engineering studies. The transmission of this knowledge is done, in many occasions, in a purely theoretical manner and posing problems to students that are disconnected from applications. In this paper we present an application of matrix formalism in acoustics: the transfer matrix method. It is a simple method widely used in transmission and reflection problems. For a system composed of a waveguide and an aluminum clamped plate subjected to the pressure of an acoustic wave, we can establish a simple connection between the matrix formalism, the use of vectors and the physical magnitudes., [ES] Las matrices se introducen en asignaturas de Matemáticas relacionadas fundamentalmente con los contenidos relativos a los espacios vectoriales y el álgebra lineal en donde las matrices aparecen desconectadas de sus aplicaciones en otros campos de la ciencia y la ingeniería. La transmisión de estos conocimientos se realiza, en muchas ocasiones, de una manera puramente teórica y planteando problemas a los alumnos que a veces son abstractos y carentes de aplicación. En este trabajo presentamos una aplicación del formalismo matricial en Acústica: el método de la matriz de transferencia. Es un método simple, ampliamente utilizado en problemas de transmisión y reflexión. Para un sistema compuesto por una guía de ondas y una placa encastrada de aluminio sometida a la presión de una onda acústica, podemos establecer una conexión simple entre el formalismo matricial, el uso de vectores y las magnitudes físicas.

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