Acoustical properties of double porosity granular materials

Venegas, Rodolfo; Umnova, Olga

doi:10.1121/1.3644915

Cited by 78 publications

(58 citation statements)

References 39 publications

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“…Unfortunately, for the sample used, the transition between isothermal and adiabatic behavior within the porous material probably lies within the measurement bandwidth. Measurements of the effective bulk modulus on smaller lead shot (1 mm diameter) using standard acoustic techniques 6 showed good correspondence between the expected isothermal value ð1=eÞ up until 300 Hz, while at higher frequencies it approached the adiabatic value. 7 Assuming that the transition frequency between isothermal and adiabatic behavior is inversely proportional to the radius squared, 8 the 3 mm lead shot used in the activated carbon study is modeled as isothermal below 33 Hz and adiabatic above.…”

Section: Lead Shotmentioning

confidence: 99%

Low frequency sound propagation in activated carbon

Bechwati

Avis

Bull

et al. 2012

The Journal of the Acoustical Society of America

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Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining the resonant frequencies of Helmholtz resonators with different backing materials. It was found that the addition of activated carbon increased the compliance of the backing volume. The effect was observed up to the highest frequency measured (500 Hz), but was most significant at lower frequencies (at higher frequencies another phenomenon can explain the behavior). An apparatus was constructed to measure the effective porosity of the activated carbon as well as the number of moles adsorbed at sound pressures between 104 and 118 dB and low frequencies between 20 and 55 Hz. Whilst the results were consistent with adsorption affecting sound propagation, other phenomena cannot be ruled out. Measurements of sorption isotherms showed that additional energy losses can be caused by water vapor condensing onto and then evaporating from the surface of the material. However, the excess absorption measured for low frequency sound waves is primarily caused by decreases in surface reactance rather than changes in surface resistance.

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Section: Lead Shotmentioning

confidence: 99%

Low frequency sound propagation in activated carbon

Bechwati

Avis

Bull

et al. 2012

The Journal of the Acoustical Society of America

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“…Liang et al [6] and Atalla et al [7] conducted quantitative analysis for acoustic characteristics of porous materials with Kolmogorov's turbulence theory, and the model was adopted to analyze wave propagation in the porous metal. Chevillotte et al [8] and Venegas et al [9] studied the effects of the three-dimensional microstructure on the sound absorption of foams, and the transport and sound absorption properties were numerically studied as a function of throat size, pore size, and sample thickness. Yang et al [10] and Kino [11] modified the Johnson-Allard model by introducing a correction factor, which could efficiently improve the prediction accuracy of the sound absorption coefficient of the porous metal.…”

Section: Introductionmentioning

confidence: 99%

Influences of Compression Ratios on Sound Absorption Performance of Porous Nickel–Iron Alloy

Bai

Shen

Zhang

et al. 2018

Metals

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Abstract:The improvement of sound absorption performance of porous metal is a focus of research in the field of noise reduction. Influences of compression ratios on sound absorption performance of a porous nickel-iron (Ni-Fe) alloy were investigated. The samples were compressed with ratios from 10% to 80% at an interval of 10%. Based on the standing wave method, sound absorption coefficients of compressed samples with different thicknesses were obtained. It could be found that with the same compression ratio, sound absorption performance was improved with the increase of thickness. Based on the modified Johnson-Allard model with a correction factor, the sound absorption coefficient of the porous Ni-Fe with a thickness of 20 mm for different compression ratios was derived, whose aim was to quantificationally analyze influences of the compression ratio. The results indicated that the sample with a compression ratio of 70% exhibited optimal sound absorption performance, and its average sound absorption coefficient reached 88.97% in a frequency range of 1000-6000 Hz. Meanwhile, the section morphologies of compressed samples were investigated by a scanning electron microscope, which studied the sound absorption performance by analyzing structures of the porous Ni-Fe samples with different compression ratios. The obtained achievements will promote the application of the porous Ni-Fe alloy in the field of acoustics.

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“…In addition, the slope of the acoustic absorption at low frequencies is steeper when the shell is microporous. This is a typical result for a double porosity medium 21,22 . The inter-scale ratio between the mesopore radius r p (air gap between the shells), and the micropore radius r µ , ε 0 = r µ /r p = 49.8.10 −3 , is small enough to be in line with the high-permeability contrast where the effects are strongest.…”

Section: Elastic Porous Shellsmentioning

confidence: 85%

Porogranular materials composed of elastic Helmholtz resonators for acoustic wave absorption

Griffiths

Nennig

Job

2017

The Journal of the Acoustical Society of America

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We present a theoretical and experimental study of the acoustic absorption of granular porous media made of non-cohesive piles of spherical shells. These shells are either rigid or elastic, possibly drilled with a neck (Helmholtz resonators), and either porous or impervious. A description is given of acoustic propagation through these media using the effective medium models proposed by Johnson (rigid particles) and Boutin (rigid Helmholtz resonators), which we extend to the configurations studied in this work. A solution is given for the local equation of elasticity of a shell coupled to the viscous flow of air through the neck and the micropores. The models and our simulations are compared to absorption spectra measured in reflection in an impedance tube. The effective medium models and our measurements show excellent agreement for configurations made of rigid particles and rigid Helmholtz resonators that induce an additional peak of absorption at low frequency. A shift of the Helmholtz resonance toward low frequencies, due to the softness of the shells is revealed by our experiments for elastic shells made of soft elastomer and is well reproduced by our simulations. We show that microporous shells enhance and broaden acoustic absorption compared to stiff or elastic resonators.

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Acoustical properties of double porosity granular materials

Cited by 78 publications

References 39 publications

Low frequency sound propagation in activated carbon

Low frequency sound propagation in activated carbon

Influences of Compression Ratios on Sound Absorption Performance of Porous Nickel–Iron Alloy

Porogranular materials composed of elastic Helmholtz resonators for acoustic wave absorption

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