Aerogel-based metasurfaces for perfect acoustic energy absorption

[EN] The unusual viscoelastic properties of silica aerogel plates are efficiently used to design subwavelength perfect sound absorbers. We theoretically, numerically and experimentally report a perfect absorbing metamaterial panel made of periodically arranged resonant building blocks consisting of a slit loaded by a clamped aerogel plate backed by a closed cavity. The impedance matching condition is analyzed using the Argand diagram of the reflection coefficient, i.e., the trajectory of the reflection coefficient as a function of frequency in the complex plane. The lack or excess of losses in the system can be identified via this Argrand diagram in order to achieve the impedance matching condition. The universality of this tool can be further exploited to design more complex metasurfaces for perfect sound absorption, thus allowing the rapid design of novel and efficient absorbing metamaterials.This work was funded by the RFI Le Mans Acoustique, Region Pays de la Loire. This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology). N.J. acknowledges financial support from Generalitat Valenciana through Grant No. APOSTD/2017/042. J.-P.G and V.R.G. gratefully acknowledge the ANR-RGC METARoom (No. ANR-18-CE08-0021) project and the HYPERMETA project funded under the program Etoiles Montantes of the Region Pays de la Loire. J.S-D. acknowledges the support of the Ministerio de Economia y Competitividad of the Spanish government and the European Union FEDER through Project No. TEC2014-53088-C3-1-RFernandez-Marin, AA.; Jimenez, N.; Groby, J.; Sánchez-Dehesa Moreno-Cid, J.; Romero García, V. (2019). Aerogel-based metasurfaces for perfect acoustic energy absorption. Applied Physics Letters. 115(6):061901-1-061901-5. https://doi.org/10.1063/1.5109084S061901-1061901-51156Gesser, H. D., & Goswami, P. C. (1989). Aerogels and related porous materials. 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Iterated maps for clarinet-like systems

The dynamical equations of clarinet-like systems are known to be reducible to a non-linear iterated map within reasonable approximations. This leads to time oscillations that are represented by square signals, analogous to the Raman regime for string instruments. In this article, we study in more detail the properties of the corresponding non-linear iterations, with emphasis on the geometrical constructions that can be used to classify the various solutions (for instance with or without reed beating) as well as on the periodicity windows that occur within the chaotic region. In particular, we find a regime where period tripling occurs and examine the conditions for intermittency. We also show that, while the direct observation of the iteration function does not reveal much on the oscillation regime of the instrument, the graph of the high order iterates directly gives visible information on the oscillation regime (characterization of the number of period doubligs, chaotic behaviour, etc.)

Investigation of Polyurea-Crosslinked Silica Aerogels as a Neuronal Scaffold: A Pilot Study

BACKGROUND: Polymer crosslinked aerogels are an attractive class of materials for future implant applications particularly as a biomaterial for the support of nerve growth. The low density and nano-porous structure of this material combined with large surface area, high mechanical strength, and tunable surface properties, make aerogels materials with a high potential in aiding repair of injuries of the peripheral nervous system. however, the interaction of neurons with aerogels remains to be investigated. METHODOLOGY: In this work the attachment and growth of neurons on clear polyurea crosslinked silica aerogels (PCSA) coated with: poly-L-lysine, basement membrane extract (BME), and laminin1 was investigated by means of optical and scanning electron microscopy. After comparing the attachment and growth capability of neurons on these different coatings, laminin1 and BME were chosen for nerve cell attachment and growth on PCSA surfaces. The behavior of neurons on treated petri dish surfaces was used as the control and behavior of neurons on treated PCSA discs was compared against it. CONCLUSIONS/SIGNIFICANCE: This study demonstrates that: 1) untreated PCSA surfaces do not support attachment and growth of nerve cells, 2) a thin application of laminin1 layer onto the PCSA discs adhered well to the PCSA surface while also supporting growth and differentiation of neurons as evidenced by the number of processes extended and b3-tubulin expression, 3) three dimensional porous structure of PCSA remains intact after fixing protocols necessary for preservation of biological samples and 4) laminin1 coating proved to be the most effective method for attaching neurons to the desired regions on PCSA discs. This work provides the basis for potential use of PCSA as a biomaterial scaffold for neural regeneration

Elastic wave propagation in a three-dimensional periodic granular medium

We present an experimental study of acoustic wave propagation in granular media made of mono-disperse spherical beads under stress and periodically arranged. A previous work presented the predominance of multiple-scattered acoustic waves for random closed-packing granular media, whereas our experimental results lead to the conclusion that the acoustical propagation in our arrangement of spherical beads proceeds essentially from surface waves. This provides another mechanism for the understanding of acoustical wave propagation in granular media, that may be useful at least to analyse weak disorder ones

SUIVI DU FONDAMENTAL DE SIGNAUX MUSICAUX À HAUTE RÉSOLUTION TEMPORELLE

le suivi du fondamental très utilisé dans le domaine du traitement de la parole reste en comparaison un outil relativement peu employé dans le cadre de l'acoustique musicale. Hormis quelques applications spécifiques, son emploi n'est souvent que le résultat d'une analyse du spectre de puissance à court terme. L'Analyse Spectrale Différentielle déjà testée en particulier dans le traitement de la parole nous a semblée autoriser une bonne précision temporelle et fréquentielle. Cette technique simple, permet d'obtenir avec des moyens légers une information précise sur l'évolution des fréquences dans le signal. Nous avons ainsi obtenu sur des signaux courts d'instruments à vent des informations sur l'évolution de la hauteur émise lors de l'attaque et pendant le son tenu ainsi que pour des variations de l'émission de pianissimo à fortissimo. On peut également, sur des phrases musicales longues, détecter très précisément la note jouée ainsi que l'écart en cents avec le tempérament égal, réalisant ainsi un détecteur de mélodie relativement simple.pitch extraction is a common tool in speech processing, but seems less used in musical acoustics. It is often obtained through short time power spectra which does not allow precise information. Differential Spectral Analysis allows an easy extraction of the main frequencies present in a signal. We have obtained upon short signals (1 second) from woodwinds, a great deal of informations on pitch variations. One also can, on long duration musical sentences, determine very precisely the note played and the discrepancy in cents with the equal tempered pitch

MESURES D'IMPÉDANCES, DE FONCTIONS DE RÉFLEXION ET D'HARMONICITÉ D'INSTRUMENTS À VENT

La méthode de mesure de l'impédance d'entrée des instruments à vent dite T.M.T.C. que nous avons développé récemment permet grâce à deux mesures simultanées de pression et à une calibration en trois points d'obtenir l'impédance d'entrée d'instruments à vent de diamètres variés avec un seul dispositif de mesure dont les imperfections géométriques acoustiques et électriques sont automatiquement prises en compte. L'utilisation systématique de la micro-informatique et de la saisie numérique permet de disposer d'un outil souple et rapide. Il est ainsi possible de calculer à partir de la mesure d'impédance la fonction de réflexion de l'instrument étudié ainsi que toute autre fonction temporelle. La mesure précise des positions des maximums d'impédance peut également être interprétée en fonction de leur rang et donner une indication sur l'harmonicité ou l'inharmonicité des résonances de l'instrument et donc sur sa qualité.We have developped recently the T.M.T.C method in order to measure the input impedance of woodwinds. This method allows us with a two pressure measurement and a three calibration technic to obtain the impedance of various diameter instruments and to correct a lot of systematics such as geometrical imperfections, microphone admittance, .... The intensive use of micro-computing and numerical acquisition gives us a powerful and fast tool. We are able to compute from the impedance the reflection function or any other time domain function. The knowledge of the frequency position of the impedance peak gives an information of the quality of an instrument by drawing the harmonicity or inharmonicity curve of the instrument

Application expérimentale du bilan de puissance réactive à la mesure de l'anche de saxophone

The reactive power balance approach is capable of linking the dynamics of a reed represented by a spring and that of the resonator which is played. A simple-reed instrument do not play exactly at the frequencies of the impedance peaks. Therefore, each mode of the pipe absorbs (or provides) reactive power. Their sum is equal to that provided by the spring which stands for the reed in our model. We have experimentally determined the input impedance of a saxophone and its internal spectrum for various notes and playing conditions. The model yields a value for the stiffness of the reed when played by a machine or a musician. The measured values are consistent with those given by the literature on isolated reeds.La notion de bilan de puissance réactive permet de lier le fonctionnement d'une anche modélisée par un ressort à celui du résonateur qu'elle excite. Un instrument à anche simple ne joue pas exactement sur les fréquences des pics d'impédance. Chaque partiel du tuyau absorbe donc (ou fournit) une puissance réactive. Leur somme algébrique est égale à celle fournie par le ressort qui représente l'anche. Sur le plan expérimental, nous avons mesuré le spectre de pression interne d'un saxophone et son impédance d'entrée pour différentes notes et nuances. La modélisation précédente permet d'obtenir une détermination de la raideur de l'anche en situation de jeu. Les valeurs mesurées sont voisines de celles relevées dans la littérature sur des anches isolées

ANALYSE TEMPORELLE DES SIGNAUX ÉMIS PAR DES SYSTÈMES ANCHES RÉSONNATEURS

L'étude des signaux acoustiques musicaux émis par des systèmes anche couplée à un résonateur est envisagée dans le domaine temporel. Les progrès techniques de l'acquisition numérique réalisés ces dernières années permettent désormais d'étudier finement les événements temporels et d'effectuer des mesures précises sur les signaux. Nous avons étudié deux systèmes différents : le premier non entretenu, la guimbarde et le second entretenu, (donc à couplage non linéaire) la clarinette. Les deux donnent des résultats similaires qui s'intègrent facilement dans un schéma même très simple du fonctionnement de l'instrument. Il devient dès lors possible d'envisager des mesures de caractéristiques mécaniques sur les anches en fonctionnement.We have studied the signals produced by musical acoustical systems with a reed coupled to a resonator in a temporal point of view. With the help of modern numerical systems of acquisition we are now able to obtain precise measurements upon the time, domain signal. We have studied two different systems : a jew-harp and a clarinet (which is a non linear system). These instruments give the same kind of results which can be easily understand with a very simple model of their functionnement. So it is possible with such an analysis to obtain informations on the behavior of reeds during the production of sound

Wave Guide Imaging through Time Domain Topological Energy

AbstractTime Domain Topological Energy (TDTE), uses a measure of the reflected ultrasonic field on an array of transducers placed on the boundary of the imaged medium. Two numerical determinations (direct and adjoint problems) of the acoustical field inside a reference medium are then necessary to obtain the image by computing the topological energy. This technique comes from the field of shape optimisation and mathematical developments for Non Destructive Testing and have shown close links with Time Reversal (TR) concepts. TR mirrors have been employed for various applications in a wide number of situations including wave guides (WG) where very good refocalisation performances have been obtained with a reduced number of transducers instead of an array. Moreover recent works have enlighten that the reverberation properties of a WG allow to re-focalise using TR with only one transducer. For TDTE imaging we choose to model a single transducer placed at one end of a wave guide. The boundaries of the WG create virtual sources that can be understood as a virtual array of transducers. Results obtained numerically for imaging using both TDTE and one transducer in a wave guide with increasing complexity : a hard spherical object and a set of three identical objects placed at the angles of an equilateral triangle are presented and preliminary experimental results are discussed

Elastic-wave transmission through self-similar anisotropic Cantor-like multilayers

Through the study of elastic wave propagation in Cantor-like anisotropic multilayers, this work analyzes the influence of medium geometry on the transmission of elastic waves to yield a better understanding of the connection between topological ordering and physical properties. Cantor-like multilayers, whose homothetic dimension is modified by changing the length of the central segment, are made of one anisotropic material with two orientations. The influence of the combination of self-similarity and anisotropy on the global transmission is investigated by means of iteration order, homothetic dimension and layer orientations. The propagation is described by the stiffness matrix algorithm. The results reveal that the homothetic dimension scales the resonance frequencies and the frequency ranges of the pseudo band gaps, and that layer orientation influences the speed of quasi-transverse waves to enhance the effect of self-similarity. Finally, an extensive study on various frequency ranges is conducted. It is demonstrated that self-similarity may be used to tune the position and the width of the pseudo band gaps to minimize the global acoustic transmission