7 results on '"*ATTENUATION (Physics)"'
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2. Pulse-echo method cannot measure wave attenuation accurately.
- Author
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Pal, Barnana
- Subjects
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SOUND waves , *ATTENUATION (Physics) , *PHYSICAL constants , *THEORY of wave motion , *DIFFRACTIVE scattering , *NUMERICAL analysis - Abstract
A number of techniques with different degrees of accuracies have been devised for the measurement of acoustic wave attenuation in solids and liquids. Still, a wide variation is observed in the attenuation values in different materials reported in the literature. Present numerical study based on a ‘propagating wave’ model analysis clearly shows that the attenuation constant obtained from exponential fitting of the echo heights in pulse-echo method differs from the exact value of intrinsic attenuation in the medium, even in the ideal situation of plane wave propagation without diffraction, dispersion or scattering. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
3. Laser-speckle-visibility acoustic spectroscopy in soft turbid media.
- Author
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Wintzenrieth, Frédéric, Cohen-Addad, Sylvie, Le Merrer, Marie, and Höhler, Reinhard
- Subjects
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SOUND waves , *THEORY of wave motion , *ATTENUATION (Physics) , *PAIRING correlations (Nuclear physics) , *TISSUES - Abstract
We image the evolution in space and time of an acoustic wave propagating along the surface of turbid soft matter by shining coherent light on the sample. The wave locally modulates the speckle interference pattern of the backscattered light, which is recorded using a camera. We show both experimentally and theoretically how the temporal and spatial correlations in this pattern can be analyzed to obtain the acoustic wavelength and attenuation length. The technique is validated using shear waves propagating in aqueous foam. It may be applied to other kinds of acoustic waves in different forms of turbid soft matter such as biological tissues, pastes, or concentrated emulsions. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
4. A simple absorbing layer implementation for transmission line matrix modeling.
- Author
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Guillaume, Gwenaël and Picaut, Judicaël
- Subjects
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ELECTRIC lines , *SOUND waves , *THEORY of wave motion , *ATTENUATION (Physics) , *DAMPING (Mechanics) , *BOUNDARY value problems , *COMPUTER simulation - Abstract
Abstract: An absorbing layer formulation for transmission line matrix modeling is proposed. The approach consists in attenuating the incident pulse propagating toward the absorbing layer only, using an attenuation factor which gradually decreases as the sound wave propagates along the absorbing medium. The formulation of the damping function followed by the attenuation factor along the absorbing layer is depicted and discussed. The efficiency of the present formulation is validated by comparison with another absorbing layer model and virtual boundary conditions proposed in the literature. Numerical simulations are also given in order to evaluate the effects of both the attenuation factor and the depth on the absorbing layer efficiency. As expected, results are consistent with absorbing layer implementation in other numerical methods; firstly, the attenuation at the entrance of the absorbing layer must be gentle, and secondly the efficiency increases with the layer depth. Lastly, it is shown that the unwanted reflection seems to vanish over the time when increasing the layer depth, meaning that reflections continuously occur within the absorbing layer and not on the geometrical limits of the absorbing layer. Although the approach is dedicated to outdoor sound propagation modeling (only an example on urban acoustics application is given), the proposed formulation of absorbing layers can be applied in other domains of acoustics. However, its application in shielded areas should be avoided because unwanted reflections due to an insufficient attenuation can be significant in comparison with the ambient noise in such quiet environments. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
5. The self-consistent dynamic problem of estimating the damage of a material by an acoustic method.
- Author
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Erofeev, V. I. and Nikitina, E. A.
- Subjects
- *
SOUND waves , *VIBRATION (Mechanics) , *THEORY of wave motion , *ATTENUATION (Physics) , *DEFORMATIONS (Mechanics) - Abstract
An approach is proposed for formulating the self-consistent problem on the basis of equations that describe the dynamics of a material and the state of its defects. It is shown that the damage of the material gives rise to frequency-dependent attenuation and phase velocity dispersion of an ultrasonic wave propagating in it. This makes it possible to estimate the damage by means of the acoustic method. The applied deformation field leads to accumulation of defects. A kinetic equation is derived for describing the damage growth, which proves to be an exponential process. The parameters of the system for which the accumulation of defects can approximately be considered as linear are estimated. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
6. On the Non-Isentropic Sound Waves Propagation in a Cylindrical Tube Filled with Saturated Porous Media.
- Author
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H. Duwairi
- Subjects
SOUND waves ,THEORY of wave motion ,ENGINE cylinders ,TUBES ,POROUS materials ,CAPILLARITY ,VARIATIONAL principles ,SHEAR (Mechanics) ,ATTENUATION (Physics) - Abstract
Abstract A rigid frame, cylindrical capillary theory of sound propagation in porous media that includes the nonlinear effects of the Forchheimer type is laid out by using variational solutions. It is shown that the five main parameters governing the propagation of sound waves in a fluid contained in rigid cylindrical tubes filled with a saturated porous media are: the shear wave number, $${s = R\sqrt{{\overline{\rho}\omega/\mu}}}$$ , the reduced frequency parameter, $${k = {wR}/\overline{a}}$$ , the porosity, ε, Darcy number, $${Da = R/\sqrt{K}}$$ , and Forchheimer number, $${C_F^\ast =2C_F}$$ . The manner in which the flow influences the attenuation and the phase velocities of the forward and backward propagating non-isentropic acoustic waves is deduced. It is found that the inclusion of the solid matrix increases wave’s attenuations and phase velocities for both forward and backward sound waves, while increasing the porosity and the reduced frequency number decreased attenuation and increased phase velocities. The effect of the steady flow is found to decrease the attenuation and phase velocities for forward sound waves, and enhance them for the backward sound waves. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
7. STATISTICAL ANALYSIS OF ACOUSTIC WAVE PARAMETERS NEAR SOLAR ACTIVE REGIONS.
- Author
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M. Cristina Rabello-Soares, Richard S. Bogart, and Philip H. Scherrer
- Subjects
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SOUND waves , *THEORY of wave motion , *MAGNETIC fields , *ATTENUATION (Physics) , *SEISMOLOGY - Abstract
In order to quantify the influence of magnetic fields on acoustic mode parameters and flows in and around active regions, we analyze the differences in the parameters in magnetically quiet regions nearby an active region (which we call “nearby regions”), compared with those of quiet regions at the same disk locations for which there are no neighboring active regions. We also compare the mode parameters in active regions with those in comparably located quiet regions. Our analysis is based on ring-diagram analysis of all active regions observed by the Helioseismic and Magnetic Imager (HMI) during almost five years. We find that the frequency at which the mode amplitude changes from attenuation to amplification in the quiet nearby regions is around 4.2 mHz, in contrast to the active regions, for which it is about 5.1 mHz. This amplitude enhacement (the “acoustic halo effect”) is as large as that observed in the active regions, and has a very weak dependence on the wave propagation direction. The mode energy difference in nearby regions also changes from a deficit to an excess at around 4.2 mHz, but averages to zero over all modes. The frequency difference in nearby regions increases with increasing frequency until a point at which the frequency shifts turn over sharply, as in active regions. However, this turnover occurs around 4.9 mHz, which is significantly below the acoustic cutoff frequency. Inverting the horizontal flow parameters in the direction of the neigboring active regions, we find flows that are consistent with a model of the thermal energy flow being blocked directly below the active region. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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