A finite element model to improve noise reduction based attenuation measurement of earmuffs in a directional sound field

The real attenuation of hearing protection devices (HPD) can be assessed in the field using a method based on continuous field microphone-in-real-ear (F-MIRE) measurements. The two-microphone method provides an indicator called the measured noise reduction (NR∗), defined as the difference between the measured exterior (outside the protector) and interior (under the protector) sound pressure levels (SPL). The HPD's attenuation expressed in terms of the more common insertion loss (IL) can then be obtained from NR∗ using compensation factors. For earmuffs, NR∗ has been shown to vary of up to 20 dB depending on the angle of incidence of the sound source. Therefore, there is a need to use sound incidence dependent compensation factors to relate NR∗ and IL. To evaluate these factors and more generally to improve the continuous F-MIRE method, a finite-element (FE) model of an earmuff on an ATF (acoustic test fixture) exposed to a directional sound field has been developed and its predictions compared with lab measurements for several incidence angles. Regarding the external microphone SPL and the NR∗, in one-third of octave bands, the model correlates very well with measurements for frequencies below 1250 Hz whatever the sound incidence. Above 1250 Hz, the FE model captures the trends, as a function of the incidence angle, but the agreement generally decreases with increasing frequency. A better correlation between the FE model and the experimental data is achieved for the variation of NR∗ (ΔNR∗) as a function of the sound incidence. Actions, such as (i) accounting for the headband in the model, (ii) refining the modeling of the sound source, (iii) improving the cushion modeling and (iv) better describing the backplate/cushion coupling conditions, are suggested to improve the model accuracy. To illustrate the potential of the modeling to improve the continuous F-MIRE measurement method, the FE model is used to determine an optimal position of the external microphone and to obtain estimates of exposure levels using the left and right ear exterior microphones. © 2016 Elsevier Lt

How reproducible is the acoustical characterization of porous media?

There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of Science(TM) (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory measurements were performed on the same material specimens so that the naturally occurring inhomogeneity in materials was controlled. It also presented the reproducibility data for the characteristic impedance, complex wavenumber, and for some related pore structure properties. This work can be helpful to better understand the tolerances of these material characterization procedures so improvements can be developed to reduce experimental errors and improve the reproducibility between laboratories

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Highlights lecture EANM 2015: the search for nuclear medicine’s superheroes

The EANM 2015 Annual Congress, held from October 10th to 14th in Hamburg, Germany, was outstanding in many respects. With 5550 participants, this was by far the largest European congress concerning nuclear medicine. More than 1750 scientific presentations were submitted, with more than 250 abstracts from young scientists, indicating that the future success of our discipline is fuelled by a high number of young individuals becoming involved in a multitude of scientific activities. Significant improvements have been made in molecular imaging of cancer, particularly in prostate cancer. PSMA-directed PET/CT appears to become a new gold standard for staging and restaging purposes. Novel tumour specific compounds have shown their potential for target identification also in other solid neoplasms and further our understanding of tumour biology and heterogeneity. In addition, a variety of nuclear imaging techniques guiding surgical interventions have been introduced. A particular focus of the congress was put on targeted, radionuclide based therapies. Novel theranostic concepts addressing also tumour entities with high incidence rates such as prostate cancer, melanoma, and lymphoma, have shown effective anti-tumour activity. Strategies have been presented to improve further already established therapeutic regimens such as somatostatin receptor based radio receptor therapy for treating advanced neuroendocrine tumours. Significant contributions were presented also in the neurosciences track. An increasing number of target structures of high interest in neurology and psychiatry are now available for PET and SPECT imaging, facilitating specific imaging of different subtypes of dementia and movement disorders as well as neuroinflammation. Major contributions in the cardiovascular track focused on further optimization of cardiac perfusion imaging by reducing radiation exposure, reducing scanning time, and improving motion correction. Besides coronary artery disease, many contributions focused on cardiac inflammation, cardiac sarcoidosis, and specific imaging of large vessel vasculitis. The physics and instrumentation track included many highlights such as novel, high resolution scanners. The most noteworthy news and developments of this meeting were summarized in the highlights lecture. Only 55 scientific contributions were mentioned, and hence they represent only a brief summary, which is outlined in this article. For a more detailed view, all presentations can be accessed by the online version of the European Journal of Nuclear Medicine and Molecular Imaging (Volume 42, Supplement 1)

Effets d'un fluide en écoulement uniforme sur le comportement vibro-acoustique d'une plaque bafflée couplée à une cavité rectangulaire

The purpose of this work is to develop a general formulation to deal with the vibro-acoustic behavior of a baffled plate, immersed on one side in a mean flow and coupled on the other side to a rectangular cavity with arbitrary wall impedances. The plate is excited by a plane wave convected by the mean flow. The formulation is based on a finite element method for the calculation of the transverse vibrations of the plate and the acoustic field inside the cavity. The external fluid loading is accounted for through the extended Kirchoff-Helmoltz integral equation and the radiation impedance of the plate in the external fluid is computed with a boundary element method. The mean flow effects on the transmission loss of the plate are discussed

Application of generalized complex modes to the calculation of the forced response of three-dimensional poroelastic materials

International audienceFinite element models based on Biot's {u,P} formulation for poroelastic materials are widely used to predict the behaviour of structures involving porous media. The numerical solution of such problems requires however important computational resources and the solution algorithms are not optimized. To improve the solution process, a modal approach based on an extension of the complex modes technique has been proposed recently and applied successfully to a simplified mono-dimensional problem. In this paper, this technique is investigated in the case of three-dimensional poroelastic problems. The technique is first recalled, then analytical proof of the stability of the model are given followed by considerations of numerical improvements of the method. An energetic interpretation of the generalized complex modes is then given and some numerical results are presented to illustrate the performance of the approach

Microscopic and mesoscopic approaches for describing and building sound absorbing porous materials

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Rayonnement acoustique de structures non bafflées

If the simulation of the radiated field of a baffled plane structure has been deeply studied, the unbaffled case, although more realistic, has retained little attention. The proposed works tend to simulate, by an analytical approach, the radiation of a plane unbaffled structure of finite dimensions and general elastic type of boundary conditions. This approach is based on an integral method coupled with a Ritz approach for the calculus of the displacement field of the structure. The power is evaluated through the pressure jump across the plate. Translation and rotational springs create varying boundary conditions. A good comparison is found with a numerical approach (B.E.M.). Parametric studies showed the effect of the baffle. Precise measurements confirm the validity of the simulations