Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Holes Interaction Effects under high and medium Sound Intensities for Micro-perforated panels design
2010
International audience; Most models for predicting the acoustic response of perforated panels are based on the assumption that there are no interactions between the holes. This paper investigates the Hole Interaction Effect (HIE) and distribution effect on the sound absorption coefficient of perforated panels when submitted to medium and high sound pressure levels. It is experimentally demonstrated that though the HIE is mostly an added mass effect, the nonlinear resistance parameters depend on the separation distance between the apertures. Analysis of the data reveals the fact that even with HIE, the nonlinear reactance dependency with velocity is very low compared to the resistance-veloci…
Characterization of porous absorbent materials
2012
International audience; Over the past twenty years, theoretical and experimental research on the acoustical properties of air-saturated porous materials for engineering applications has considerably progressed thanks to the contributions of many researchers in different institutes in the world. Accompanying the research on the acoustical properties of absorbent materials, new methods and experimental techniques were developed for the measurement of important physical parameters of these materials, necessary for the acoustic models. The attention is focused on the particularly important contributions of two laboratories: the Laboratoire dAcoustique de lUniversité du Maine (LAUM) in France …
Acoustic properties of perforated plates and screens
2012
International audience; In previous works, an acoustic model for Microperforated Insertion Unit (MIU), was developed to determine the input impedance of a system composed of a thin mesh (or screen) glued onto a perforated plate. An alternative approach is proposed by means of the equivalent fluid model of Johnson-Champoux-Allard involving five physical parameters: the tortuosity, the thermal and viscous characteristic lengths, the porosity and the flow resistivity. The input impedance of a multiple layer system can then be found by use of the transfer matrix method. Since the meshes have fairly simple structures, it was possible to model an elementary representative cell and to use calculat…
Acoustic properties of plates with unevenly distributed macro perforations backed by woven meshes
2012
A hybrid model describing the acoustic properties of plates with macro-perforations that can be unevenly distributed on the plate surface and backed by woven or precision woven meshes with microscopic perforations is proposed. The plate perforations may be of circular or rectangular shapes. Since the perforated plate may not necessarily be considered as an equivalent fluid, its surface impedance is calculated by the Maa model [Noise Control Eng. J. 29, 77-84 (1987)], whereas the Johnson-Champoux-Allard model [J. Appl. Phys. 70, 1975-1979 (1991)] is used for the mesh. It is observed that the absorption of the carrying plate seems to depend on the hydraulic diameter of the perforations and no…
Surface and guided waves in porous materials
2010
National audience; The last decades, a lot of research has been done about the propagation of sound in heterogeneous and porous materials. Especially the two-phase nature of the poro-elastic material leads to interesting physical phenomena. During recent years, several measuring methods have been developeded to determine the material parameters. However, a lot of problems aren't solved yet. Because of the visco-elastic behavior of a lot of these materials, the elastic moduli will become frequency dependent (rubberlike behavior at low frequencies and glasslike behavior at high frequencies). Experimental data about the frequency- and temperature dependence of the elastic moduli are scarce bec…
On the measurement and prediction of the sound absorption coefficient of air-cavity backed perforated plates considering the holes interaction effect…
2012
International audience; This paper deals with the measurement and prediction of air cavity backed perforated plates considering the holes interaction effect under relatively low sound excitation. A revised expression for the radiation contribution is proposed to properly account for the holes interaction effect. This expression is integrated in the characteristic impedance expression following Atalla and Sgard [J. Sound Vib. 303, 195-208 (2007)] model. Perforated plate specimens with different centre-to-centre holes distances (pitches) are built and tested using an impedance tube. The particular cases of holes interaction effect with constant low porosity and of holes interaction effect wit…
Sound absorption coefficient of a porous material covered with a low open area perforated plate under high sound excitation
2012
International audience; The sound absorption coefficient of porous materials covered with low open area perforated plate is studied under high sound intensities in the absence of mean flow. The theoretical considerations are based on the equivalent fluid following the Johnson-Champoux-Allard approach and the use of the transfer matrix method. To take into account the high sound levels effects, the air flow resistivity of each layer is modified following the Forchheimer law. Two specimens of perforated plate are built and tested when backed by a polymeric foam and a fibrous material. A specific impedance tube setup is developed for the measurement of the surface acoustic impedance for sound …
Dielectric properties of graphite-based epoxy composites
2014
International audience; Composite materials based on epoxy resin filled with various kinds of graphite particles: exfoliated graphite, natural graphite, and coarse, medium and fine artificial graphites have been prepared. Results of broadband dielectric investigations of such materials in wide temperature (25-450 K) and frequency (20 Hz-3 THz) ranges are presented. The dielectric permittivity strongly increases with graphite particle size. The graphite particle size and shape also have a strong impact on freezing temperature, conductivity activation energy and composite electromagnetic absorption properties at room temperature. The lowest percolation threshold is observed for exfoliated gra…
Indoor noise exposure assessment of primary school children living in a french urban area
2012
International audience; The recent development of powerful noise mapping softwares allows to assess the exposure to environmental noise at the scale of an agglomeration. However noise levels inside dwellings are still unknown at such scales. To evaluate indoor noise levels and to investigate the factors which determine them, an eight-day noise measurement campaign was carried out in 50 childrens home. These children were randomly chosen among 8 or 9-year-old pupils attending the public primary schools of Besançon (France). Microphones were placed in the childs bedroom, outdoor in front of the bedrooms facade, and in the main room. Equivalent sound pressure levels (LAeq) were calculated d…
Acoustic Topological Circuitry in Square and Rectangular Phononic Crystals
2021
International audience; We systematically engineer a series of square and rectangular phononic crystals to create experimental realizations of complex topological phononic circuits. The exotic topological transport observed is wholly reliant upon the underlying structure which must belong to either a square or rectangular lattice system and not to any hexagonal-based structure. The phononic system chosen consists of a periodic array of square steel bars which partitions acoustic waves in water over a broadband range of frequencies (∼0.5MHz). An ultrasonic transducer launches an acoustic pulse which propagates along a domain wall, before encountering a nodal point, from which the acoustic si…