Localization of radiating sources by an acoustical array

International audienceArrays of sensors are used in many fields to detect signals, to resolve closely spaced targets, to estimate the bearing, the position, the strength and other properties of radiating sources whose signals arrive from different directions. The purpose of the work described in the communication is to provide estimators which are used to localize acoustical sources by an acoustical array of sensors. These estimators are based on acoustic processing algorithms: the conventional beamforming, the Minimum Variance and the constrained Capon algorithm. It is shown that these adaptive algorithms can detect radiating sources which are not detectable by classical weighted arrays of sensors. Numerical results are presented

Antenne acoustique et parcimonie lors de la localisation de sources sonores

Un réseau de microphones constitue une antenne acoustique et sert d’interface entre l’environnement physique et les signaux mesurables. Ces signaux sont alors exploités afin de réaliser une imagerie du champ acoustique incident. Cette imagerie est soit purement spatiale, si elle ne fournit d’information que sur les directions des sources, leurs distances et leurs intensités sonores dans une bande fréquentielle, soit spatio-fréquentielle, si elle fournit en outre une information concernant les répartitions spectrales des signaux qu’elles émettent. Nous nous proposons de présenter les principales méthodes de traitement d’antenne acoustique à haute résolution spatiale et fréquentielle. Une comparaison des algorithmes en termes de pouvoir de résolution et de biais est analysée. Les avantages et les inconvénients de chaque algorithme sont exposé

Anodic bonding using SOI wafer for fabrication of capacitive micromachined ultrasoonic transducers

International audienceIn medical ultrasound imaging, mostly piezoelectric crystals are used as ultrasonic transducers. Capacitive micromachined ultrasonic transducers (CMUTs) introduced around 1994 have been shown to be a good alternative to conventional piezoelectric transducers in various aspects, such as sensitivity, transduction efficiency or bandwidth. This paper focuses on a fabrication process for CMUTs using anodic bonding of a silicon on insulator wafer on a glass wafer. The processing steps are described leading to a good control of the mechanical response of the membrane. This technology makes possible the fabrication of large membranes and can extend the frequency range of CMUTs to lower frequencies of operation. Silicon membranes having radii of 50, 70, 100 and 150 µm and a 1.5 µm thickness are fabricated and electromechanically characterized using an auto-balanced bridge impedance analyzer. Resonant frequencies from 0.6 to 2.3 MHz and an electromechanical coupling coefficient around 55% are reported. The effects of residual stress in the membranes and uncontrolled clamping conditions are clearly responsible for the discrepancies between experimental and theoretical values of the first resonance frequency. The residual stress in the membranes is determined to be between 90 and 110 MPa. The actual boundary conditions are between the clamped condition and the simply supported condition and can be modeled with a torsional stiffness of 2.10−7 Nm rad-1 in the numerical model

Localisation de sources sonores par représentation parcimonieuse

On se propose de localiser des sources sonores par représentation parcimonieuse des données temporelles provenant des microphones formant une antenne acoustique. Les sources sont corrélées ou non corrélées, à bande étroite ou bien à large bande. Des exemples de simulation et des tests en chambre anéchoïque sont présentés montrant les performances des algorithmes proposés. Ces algorithmes sont comparés aux algorithmes traditionnels tels que beamforming, Capon et MUSIC

Comportement vibratoire des pièces tournantes à l'aide de données sous-échantillonnées

Dans le cadre de la surveillance vibratoire des roues aubagées de turbines, l'analyse par mesure optique des temps de passage des aubes permet d'étudier les modes vibratoires d'une roue aubagée en fonctionnement. A partir d'un jeu de capteurs disposés sur le carter en regard de l'aubage, on peut en déduire l'amplitude vibratoire de chaque pale au passage devant le capteur. La principale difficulté d'un tel signal est qu'il est fortement sous-échantillonné et replié. On se propose dans cette étude d'appliquer des méthodes de la théorie de l'échantillonnage non-uniforme pour des structures à support fréquentiel multi-bande afin de diminuer les effets du repliement

Calcul du rayonnement acoustique des transducteurs capacitifs ultrasonores micro-usinés

Les transducteurs ultrasonores capacitifs micro-usinés (CMUT) sont une alternative prometteuse aux transducteurs piezo-électriques. Ils sont constitués d'un très grand nombre de micro-membranes organisées en réseau et actionnées électrostatiquement. Nous proposons une méthode de calcul originale permettant de déterminer la pression acoustique émise par le réseau en prenant en compte explicitement l'effet de chaque micro-membrane. Les performances de la méthode sont démontrées sur des transducteurs typiques

Qualitative Analysis of Forced Response of Blisks With Friction Ring Dampers

A damping strategy for blisks (integrally bladed disks) of turbomachinery involving a friction ring is investigated. These rings, located in grooves underside the wheel of the blisks, are held in contact by centrifugal loads and the energy is dissipated when relative motions between the ring and the disk occur. A representative lumped parameter model of the system is introduced and the steady-state nonlinear response is derived using a multi-harmonic balance method combined with an AFT procedure where the friction force is calculated in the time domain. Numerical simulations are presented for several damper characteristics and several excitation configurations. From these results, the performance of this damping strategy is discussed and some design guidelines are given

Association between Ambient Noise Exposure and School Performance of Children Living in An Urban Area: A Cross-Sectional Population-Based Study

16 pages Article disponible à l'adresse suivante : http://link.springer.com/article/10.1007%2Fs11524-013-9843-6International audienceMost of the studies investigating the effects of the external noise on children's school performance have concerned pupils in schools exposed to high levels due to aircraft or freeway traffic noise. However, little is known about the consequences of the chronic ambient noise exposure at a level commonly encountered in residential urban areas. This study aimed to assess the relationship between the school performance of 8- to 9-year-old-children living in an urban environment and their chronic ambient noise exposure at home and at school. The children's school performances on the national standardized assessment test in French and mathematics were compared with the environmental noise levels. Children's exposure to ambient noise was calculated in front of their bedrooms (Lden) and schools (LAeq,day) using noise prediction modeling. Questionnaires were distributed to the families to collect potential confounding factors. Among the 746 respondent children, 586 were included in multilevel analyses. On average, the LAeq,day at school was 51.5 dB (SD= 4.5 dB; range = 38-58 dB) and the outdoor Lden at home was 56.4 dB (SD= 4.4 dB; range = 44-69 dB). LAeq,day at school was associated with impaired mathematics score (p = 0.02) or impaired French score (p = 0.01). For a + 10 dB gap, the French and mathematics scores were on average lower by about 5.5 points. Lden at home was significantly associated with impaired French performance when considered alone (p < 10(-3)) and was borderline significant when the combined home-school exposure was considered (p = 0.06). The magnitude of the observed effect on school performance may appear modest, but should be considered in light of the number of people who are potentially chronically exposed to similar environmental noise levels