Johnson-Allard Model Research Articles

Sound absorption model of foam glass-ceramics based on microstructure

Foam glass-ceramics have the characteristics of broadband sound absorption, lightweight and high-strength, which can be utilized in sound barriers on traffic networks. Due to the complexity of microstructure, there is no sound absorption model suitable for foam glass-ceramics at present. In order to realize the prediction of sound absorption performance, a sound absorption model based on Johnson-Allard model was studied in this paper. The results show that the sound absorption coefficient of foam glass-ceramics only can be accurately predicted by Johnson-Allard model in a relatively low frequency band (500∼1250 Hz). Therefore, to broaden the applicability of the model to acoustic frequencies, three sub-structure factors were introduced to modify Johnson-Allard model with the influence of microstructure on the sound absorption performance fully considered. The results show that the modified Johnson-Allard model has high accuracy in predicting the sound absorption coefficient of foam glass-ceramics in the full frequency band of traffic network noise.

Sensitivity of acoustic parameters on the reflected signal from a rigid porous medium in the low-frequency range of ultrasound

Porous materials are two-phase media consisting of pores saturated with a fluid emerging from a solid skeleton. There are several parameters describing the porous medium. These parameters are classified into two categories: the high-frequency parameters and the low-frequency parameters. During the excitation by an acoustic wave, two cases can occur; the vibration of both phases simultaneously in the case where the structure is flexible, this case is well studied by Biot theory. For a rigid structure, it is the movement of the fluid that is taken into account; this last case is treated by the equivalent fluid theory which is a particular case of Biot theory. Previous work [Proc. Mtgs. Acoust. 45, 045004 (2021)] has shown the influence of the parameters involved in the corrected Johnson-Allard model recently introduced by Sadouki [Phys. Fluids 33, (2021)] on the transmitted signal from a rigid-porous material in the low-frequency regime of ultrasound. The objective of this work is to show, once again, the influence of the same parameters on the reflected signal by providing a comparative study between transmitted and reflected modes.

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

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.

Geometrical and Dimensional Optimization of Sound Absorbing Porous Copper with Cavity

Optimization of sound absorbing coefficient of porous copper under a limited dimension is focus of research in the fields of acoustics and mechanics. Through measuring the sound absorbing coefficient based on the standing wave method, 5 groups of experiments are conducted to investigate the sound absorbing property of the porous copper with cavity under a limited dimension of 30mm. There are two options can meet the requirement that the sound absorbing coefficients are larger than 70% in 2000-5000Hz. First is the pure porous copper with thickness of 30mm, and the other is the combination of porous copper with thickness of 25mm and cavity with thickness of 5mm. Based on the modified Johnson-Allard model with correction factor, it can be obtained that theoretical optimal thickness of the pure porous copper is 28.8mm, and the theoretical optimal combination of porous copper and cavity are 22.7mm and 7.3mm. Experimental validations indicate that the two optimal options of the two modes both can meet the sound absorbing requirement. The results will promote the application of porous copper and improve the sound absorbing theory of porous material.

Sound absorption characteristics of multilayer porous metal materials backed with an air gap

A sound absorbing structure of multilayer porous metal materials backed with an air gap is proposed to enhance the normal incidence sound absorption performance. The new sound absorbing structures could improve the sound absorption coefficient in a low frequency range and decrease the fluctuation of the sound absorption coefficient in a high frequency range. The Johnson-Allard model is employed to study the sound absorption characteristics of the porous metal materials. And acoustic wave transmitting in the porous metal materials obeys the law of acoustic wave propagation. The sound absorption coefficient and normalized acoustic impedance of the multilayer porous metal materials with or without an air gap are analyzed theoretically, and then compared with existing experimental values. Furthermore, the influence of several physical parameters on sound absorption characteristics, such as the thickness of the air gap, the number of layers, thickness, porosity and flow resistivity of the porous metal materials, are evaluated. The results indicate that the sound absorbing structures of the multilayer porous metal materials backed with an air gap present a satisfying sound absorption characteristic over a wide frequency range.

Acoustic Properties of Innovative Material from Date Palm Fibre

Problem statement: An organic material is one of the major requiremen ts to improve living environment and the invention of materials need to consider for the best solution. This study presents an experimental investigation on pure porous from D ate Palm Fibre (DPF). The effectiveness of sound absorbers depends on structural architecture of thi s material. This study was conducted to examine the potential of using date palm fibre as sound absorbe r. The effects of porous layer thicknesses, densiti es and compression on Acoustic Absorption Coefficient (AAC) of sound absorber using date palm fibre were studied. Approach: Rigid frame Johnson-Allard Model for various sample thicknesses was used in this study. The measurements were conducted in i mpedance tube on normal incidence acoustic absorption. The date palm fibre was mixed with late x which used for physical treatment on this material. Acoustic absorption behaviour of a porous material with different thicknesses was studied as well as samples with same thickness but different d ensities. In addition, samples with same properties but different period of compression time were inspe cted. The tests were in accordance to ISO 10534-2 and ASTM E1050-98 international standards for Acoustic Absorption Coefficient (AAC). Results: The experimental data indicates that two peak valu es of AAC is 0.93 at 1356Hz for sample with 50 mm thickness, also the AAC at high frequency for sa me thickness is 0.99 at 4200-4353 Hz that means able to improve acoustic absorption coefficient at low and high frequencies with significant increasin g. Meanwhile, another experimental results were acquir ed for AAC of date palm fibre, with samples thicknesses of 35 mm at different densities .The re sults show that denser sample (11 Kg m -3 ) has higher AAC value of 0.83 at 1934- 2250 Hz as compared to less dense sample (9.92 Kg m -3 ) with AAC value 0.84 at 2443-2587 Hz . Conclusion: Acoustic absorption coefficient AAC of date palm fibre was increased at all frequencies when the thi ckness of sample was increased, particularly at low frequencies less than 1200 Hz. The introduction of latex on the samples adds stiffness, so that sound can be dissipated significantly as it travels throu gh material. Results from the experimental tests sh ow that date palm fibre has good acoustic properties a t low and high frequencies and can be used as an alternative replacement to conventional product. In creasing density of the samples, increase the AAC as well. The innovative acoustic absorption panel has a good potential because they are cheaper and lighter in comparison to asbestos and rock wool ind ustrial materials.

Sound absorption characteristics of a high-temperature sintering porous ceramic material

This article is dedicated to sound absorption properties of porous zeolite with macropores, a ceramic material fabricated by high-temperature sintering. Acoustical properties of this ceramic material are studied by two analytical models, Delany–Bazley model and Johnson–Allard model, where the latter one shows a better fit to the experimental results. Moreover increasing the thickness of samples would improve the sound absorption in the low frequency ranges. Raising the porosity could increase the highest sound absorption coefficient. The resonance frequencies of the materials with 3–5mm particles are more obvious. Comparing with glass wool, porous zeolite has a better sound absorption.

Material Parameter Determination in Glass Wool Mat for Sound Absorption

Glass wool mat is widely used in the fields of building engineering, transport facilities and refrigeration equipment. In this paper, the effect of material parameters such as density, thickness, porosity, and flow resistivity on the normal incidence absorption coefficient has been studied. In addition, fiber length is also investigated to achieve appropriate strength. The prediction error of normal incidence absorption coefficient by modified Johnson–Allard model is less than 5% in the frequency range between 800 Hz and 5 kHz. We could use the modified Johnson–Allard model to determine the parameter of glass wool mat for better development.

Comparisons between characteristic lengths and fibre equivalent diameters in glass fibre and melamine foam materials of similar flow resistivity

Abstract Flow resistivity, tortuosity, viscous characteristic length and thermal characteristic length of three melamine foam and two glass wool samples have been measured. It has been found that a melamine foam sample with a bulk density 10.3 kg m−3 and a glass wool sample with a bulk density 28.0 kg m−3 have almost the same flow resistivity, however, the bulk density is as much as three times different. The cross-sectional pore shape factors, which are deduced with the non-acoustical parameters in the Johnson–Allard model, of the melamine foam are smaller than those of the glass wool. This paper also discusses a new relationship between the flow resistivity, the fibre equivalent diameter and the bulk density in melamine foam.

Improvements to the Johnson–Allard model for rigid-framed fibrous materials

Measurements of the surface impedance and the physical parameters of seven glass wool samples and six polyester fibre samples with flow resistivities between 4100 and 69,900 Pa s m −2 have been made. Comparisons of measured absorption coefficients and those predicted from the Johnson–Allard formulae using the measured and deduced physical parameters show discrepancies that exceed 20% for some samples and frequencies. By modifying the Johnson–Allard formula for effective density and by introducing a correction factor that is a function of flow resistivity based on data fitting, it has been found possible to improve the predictions. However, it has also been found that a similar modification of the formula for bulk modulus is necessary to reduce the discrepancies with data to below 5% in the frequency range between 800 Hz and 5 kHz.

Influence of dynamic tortuosity and compressibility on the propagation of transient waves in porous media

This paper provides an analytical solution in the time domain for the propagation of transient ultrasonic waves in a homogeneous, isotropic porous material with a rigid frame. The originality of this propagation equation is the use of the Pride et al. and Lafarge models, which give a better description of acoustic wave attenuation. Two parameters, p and p′, are added to the description of losses in the porous material, given a modification of coefficients of the propagation equation in the time domain. The analytical solution to the wave equation has a different form as compared with that obtained from the Johnson–Allard model. This wave equation contains fractional derivative terms describing attenuation and dispersion in porous material. The Laplace transform method is used to solve the propagation equation. An experimental application to porous plastic foam is given to validate the mathematical solution to the propagation equation. One important result of this work is that the introduction of the two parameters p and p′ corrects the Johnson–Allard model by increasing attenuation with no change in dispersion. This phenomenon is much more significant for resistive porous materials.