Design and implementation of a multi-octave-band audio camera for realtime diagnosis

Noise pollution investigation takes advantage of two common methods of diagnosis: measurement using a Sound Level Meter and acoustical imaging. The former enables a detailed analysis of the surrounding noise spectrum whereas the latter is rather used for source localization. Both approaches complete each other, and merging them into a unique system, working in realtime, would offer new possibilities of dynamic diagnosis. This paper describes the design of a complete system for this purpose: imaging in realtime the acoustic field at different octave bands, with a convenient device. The acoustic field is sampled in time and space using an array of MEMS microphones. This recent technology enables a compact and fully digital design of the system. However, performing realtime imaging with resource-intensive algorithm on a large amount of measured data confronts with a technical challenge. This is overcome by executing the whole process on a Graphic Processing Unit, which has recently become an attractive device for parallel computing

Block-sparse approach for the identification of complex sound sources in a room

International audienceGeometrical acoustic softwares are necessary to produce auralizations for specific sound environment. Whether the room impulse response computation require point-source and receiver to be of omnidirectional sensitivity, the influence of their directivity on the resulting virtual audio rendering Is relevant. It is then crucial to account for when simulating accurately a calibrate acoustic model.We treats here the case of the source directivity. The use of a spherical surrounding microphone array remains the most natural way to measure it. The source is located inside the delimiting volume. The radiated pressure is sampled at fixed points. The directivity pattern is then computed in term of spherical harmonics functions. But due to hardware complexity, most of the spherical antennas in the litterature have a few number of microphones. This limits the performance of the antenna in term of resolution and bandwidth. Also, decomposition errors can appear with a possible mismatch between the acoustic center of the source and the origin of the array. An additional optimization task is required which increases the complexity of the process.In this paper, we propose a practical strategy, comprising a dedicated algorithm and an array design, to estimate the directivity pattern of complex sound sources. The study takes place in reverberant rooms.Firstly, we describe a greedy-sparse algorithm called Block Orthogonal Matching Pursuit. By this iterative approach, the identification and characterization tasks can be joint in a unique scheme. This facilitates the acoustic center research. However, under non-anechoic conditions, BlockOMP fails because of the free-field propagation assumption. Considering the first reflections to approximate the room transfer function permits to solve the inverse problem. The notion of virtual microphone arrays, based on an analogy with the Image Source Method, is introduced to extend the validity of BlockOMP. Numerical results supply a proof of the concept in a scenario including multiple acoustic sources.Secondly, a large three-dimensional microphone array is deployed. Largeness concerns here in both its dimensions and the number of microphones. The array consists of five sub-planes which surround the entire room where sources are located. The acquisition system comprises digital MEMS microphones chips. The entire signal processing chain is directly integrated on the captor. The microphones are flush mounted on the walls of the room. The true location of the sensors is known, given by an acoustic geometrical calibration step. The 1024 MEMS record synchronously the pressure signal emitted by the sources. From each harmonic spectral component, a sparse spherical harmonics decomposition of each target can be achieved.An experiment is performed to assert the efficiency of the proposed strategy. The goal is to recover the nature of two prototypes of source. They are build from an unbaffled loudspeaker, arranged to show a dipole and a quadripole behaviour. Their directivity pattern are previously measured under controlled conditions using a semi-circular array of 64 microphones. This database serves here as reference. For the experiment, they emit the same signal simultaneous. The results with our system indicates good correlations. Separating both the sound radiating contribution is well achieved. Our last study case deals with the voice directivity measurements. If the dependence with the frequency has been established, the effect of the phonema variation is rarely identified. We demonstrate here that our apparatus constitutes a powerful tool to examine this aspect

Christianisme et philosophie - Christianity and philosophy

French Abstract: Le christianisme contrasté aux philosophies occidentales et orientales. English Abstract: Christianity contrasted to western and eastern philosophies

Evolution du niveau d'agglomération de nanopoudres d'aluminium : une approche rhéologique

National audienceFrom micrometric size to nanometric size, the increase of the surface energies allows the agglomeration to be preponderant and then, the risks linked to powders are changed. When the toxicity, the inflammation and explosion risks of nanoparticles are mentioned, the agglomerates must be taken into account. The effect of agglomeration in the behavior of nanopowders has been studied from experimental observation of agglomerated nanopowders of aluminum subjected to shear in a powder rheometer. In order to understand the effect of deagglomeration on the powders, the agglomerate strength has been estimated thanks to the porosity of the powder bed contained in the rheometer cell. This one is ranged between 10 kPa and 1 MPa. The rheological tests show that, compared with the micrometric aluminum, the aluminum nanopowders have a peculiar behavior in the Geldart's classification, being in both class A and C. This fact is due to the facility of nanoparticles to agglomerate and to stay agglomerated.Lorsque l'on passe de la dimension micrométrique à la dimension nanométrique, l'augmentation importante des énergies de surface rend prépondérants les phénomènes d'agglomération. Ceci modifie l'appréhension des risques liés aux poudres. Pour parler de toxicité, de risques d'inflammation et d'explosion des nanoparticules, nous devons prendre en compte la présence d'agglomérats. L'effet de l'agglomération sur la dispersibilité des nanopoudres a été étudié à partir d'observations expérimentales de nanopoudres agglomérées d'aluminium soumises au cisaillement fourni par un rhéomètre à poudres. Pour comprendre l'effet de la désagglomération sur les poudres, nous avons déjà estimé la contrainte d'agglomération mise en jeu à partir de la porosité du lit de poudres contenues dans la cellule du rhéomètre. Cette contrainte est globalement ici comprise entre 10 kPa et 1MPa. Les tests en rhéologie ont montré qu'en comparaison avec une poudre d'aluminium micrométrique, les nanopoudres d'aluminium ont un comportement particulier vis-à-vis de la classification de Geldart, appartenant à la fois aux classes A et C, ceci étant du à la facilité des nanoparticules à s'agglomérer et à le rester

The effect of agglomeration on the emission of particles from nanopowders flow

International audienceThis paper suggests an original method to evaluate the possible emission of particles from a nanopowder submitted to a shear stress in dense phase and the resulting degree of agglomeration of the particles released. The method is based upon the monitoring of the rheological signature of the nanopowders, thanks to a powder rheometer. As a function of the increasing shear rate, the powder flow will evolve from the newtonian state (dense powder) to the coulombian state (dense rheofluidified phase). If the shear rate is high enough, the powder will be set in suspension and the kinetic state (a leaner dense phase submitted to particles collisions) will be reached. The shear stress in this state is dependent on the particle or the agglomerate diameter for cohesive powders, which can be then calculated from rheograms. Carbon black and silica nanopowders have been tested and compared to other experiments carried out on non cohesive glass beads microparticles, chosen as reference. For the different glass beads powders, the average value of their 'agglomerate' diameter is 12% different of the primary diameter, indicating agglomeration of less than two particles. Nanometric agglomerates were found to be of hundred micrometers diameter. That is in line with the high tendency of the nanoparticles to agglomerate. This work can be used to evaluate the current safety tests, such as Hartmann's tube or 20 L sphere apparatuses, to verify whether the standard equipment for microparticles is suitable for the use of nanoparticles. This is linked to research projects like NanoSafe 2

Sparse underwater acoustic imaging: a case study

International audienceUnderwater acoustic imaging is traditionally performed with beam- forming: beams are formed at emission to insonify limited angular regions; beams are (synthetically) formed at reception to form the image. We propose to exploit a natural sparsity prior to perform 3D underwater imaging using a newly built flexible-configuration sonar device. The computational challenges raised by the high- dimensionality of the problem are highlighted, and we describe a strategy to overcome them. As a proof of concept, the proposed approach is used on real data acquired with the new sonar to obtain an image of an underwater target. We discuss the merits of the obtained image in comparison with standard beamforming, as well as the main challenges lying ahead, and the bottlenecks that will need to be solved before sparse methods can be fully exploited in the context of underwater compressed 3D sonar imaging

Marine observations with a harmonic single-beam echo-sounder

International audienceTo characterise the seabed or water-column targets with acoustics, it is common to use multiple frequencies and therefore several sonar transducers or echo-sounders. The single beam echo-sounder we present here is able, thanks to non-linearity of the sea water, to generate more than three harmonics above its fundamental transmitted frequency, in effect producing four distinct frequencies with a single echo-sounder. In addition, all transmitted signals are perfectly in phase because they are carried by the same pulse, which has obvious benefits for further processing of the echoes. In this presentation, after a short review of the entire system, its application to seabed characterisation using the reflectivity level (acoustic backscattering strength from the seafloor) will be exposed. Further developments of plans to use this echo-sounder for fishery acoustics will then be highlighted, based on datasets acquired in the Bay of Brest (France). (Project funded by ANR and DGA / ANR-14-ASTR-0022-00)