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Number of results: 15
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Abstract

Studies to find alternative low environmental-impact materials for acoustic absorbers are still progressing, particularly those originated from natural materials. However, most of the established works are mainly focused on the fibrous-type absorbers. Discussion on the non-fibrous-type absorbers is still lacking and this therefore becomes the objective of this paper. Use of bamboo by utilizing its hollow structure to absorb sound energy is discussed here. The normal incidence absorption coefficient was measured based on the length and diameter of the bamboo, as well as different arrangement of the bamboo structure subjected to the incidence sound, namely, axial, transverse, and crossed-transverse arrangements. The trend of absorption coefficient appears in peaks and dips at equally spacing frequencies. For all arrangements the peak of absorption can reach above 0.8. Introducing an air gap behind the bamboo shifts the peak absorption to lower frequency. Covering the front surface of the absorber improves the sound absorption coefficient for axial arrangement by widening the frequency range of absorption also towards lower frequency range. The transverse arrangement is found to have average absorption coefficient peaks of 0.7 above 1.5 kHz. By arranging the bamboo structure with crossed-transverse arrangement, the suppressed absorption peaks in normal transverse arrangement can be recovered.
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Authors and Affiliations

Azma Putra
Fazlin Abd Khair
Mohd Jailani Mohd Nor
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Abstract

Sound absorption coefficient is a commonly used parameter to characterize the acoustic properties of sound absorbing materials. It is defined within the frequency range of 100-5 000 Hz. In the industrial conditions, many appliances radiating acoustic energy of the frequency range of above 5000 Hz are used and at the same time it is known that a noise within the frequency range of 5 000-50 000 Hz can have a harmful effect on people,hence there is a need to define the coefficient in this frequency range. The article presents a proposal for a method of measurement of the sound absorption coefficient of materials in the frequency range from 5 000 Hz to 50 000 Hz. This method is a modification of the reverberation method with the use of interrupted noise.
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Authors and Affiliations

Witold Mikulski
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Abstract

The article presents the main results of research on plaster samples with different physical parameters of their structure. The basic physical parameter taken into account in the research is plaster aeration. Other physical parameters were also considered, but they play a minor part. The acoustic properties of the modified plaster were measured by the sound absorption coefficient; the results were compared with the absorption coefficient of standard plaster. The influence of other physical, mechanical and thermal properties of plaster was not analyzed. The effect of modified plasters on indoor acoustics was also determined. To this end, an acoustic problem with impedance boundary conditions was solved. The results were achieved by the Meshless Method (MLM) and compared with exact results. It was shown that the increase in plaster aeration translated into an increase in the sound absorption coefficient, followed by a slight decrease in the noise level in the room. Numerical calculations confirmed this conclusion.
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Bibliography

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2. Branski A. (2013), Numerical methods to the solution of boundary problems, classification and survey [in Polish], Rzeszow University of Technology Press, Rzeszow.
3. Branski A., Kocan-Krawczyk A., Predka E. (2017), An influence of the wall acoustic impedance on the room acoustics. The exact solution, Archives of Acoustics, 42(4): 677–687, doi: 10.1515/aoa-2017-0070.
4. Branski A., Predka E. (2018), Nonsingular meshless method in an acoustic indoor problem, Archives of Acoustics, 43(1): 75–82, doi: 10.24425/118082.
5. Branski A., Predka E., Wierzbinska M., Hordij P. (2013), Influence of the plaster physical structure on its acoustic properties, 60th Open Seminar on Acoustics, Rzeszów–Polanczyk (abstract: Archives of Acoustics, 38(3): 437–437).
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10. Kulhav P., Samkov A., Petru M., Pechociakova M. (2018), Improvement of the acoustic attenuation of plaster composites by the addition of shortfibre reinforcement, Advances in Materials Science and Engineering, 2018: Article ID 7356721, 15 pages, doi: 10.1155/2018/7356721.
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Authors and Affiliations

Edyta Prędka
1
Adam Brański
1
ORCID: ORCID
Małgorzata Wierzbińska
2

  1. Department of Electrical and Computer Engineering Fundamentals, Technical University of Rzeszow, Rzeszów, Poland
  2. Department of Materials Science, Technical University of Rzeszow, Rzeszów, Poland
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Abstract

The theoretical estimation of sound absorption coefficient of a surface may give very different results. This will depend on the type of sound field assumed in the theoretical model used for the estimation of its sound absorption coefficient. Absorption coefficients for normal and diffuse sound fields are widely known, although they may be far from the absorption values given by an absorbing material when it is finally installed inside a room or enclosed space, where a sound field closer to a spherical wavefront is more likely to be found. This work presents a theoretical study, which is addressed at obtaining a mathematical expression to calculate the sound absorption coefficient for a variable range of incidence angles, called αs. The presented method uses a circular sound field incidence as an approximation to a spherical incidence. The estimation of this coefficient αs is based on obtaining the incident and reflected sound fields for a surface located facing a lineal source. The advantage of this calculation method over others lies on its capability to give results for circular, normal and random wave incidence depending on the range of incidence angles considered in the calculation.

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Authors and Affiliations

Sergio Alfio Yori
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Abstract

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In2S3 thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.

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Authors and Affiliations

L. Bychto
M. Maliński
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Abstract

Considering the environmental pollution caused by waste rubber, some measures should be taken to improve the utilization rate of waste rubber. In this study, the effect of Ethylene Propylene Diene Monomer (EPDM) particles in the polyurethane (PU) foams on sound absorption behavior is investigated for improving sound environment within vehicles and reducing the environment pollution. EPDM of different contents and hardness are used as fillers for producing foams with different pore morphologies and sound absorption properties. The results show adds EPDM to foam would produce smaller pores, higher density and bigger air-flow resistivity. Simultaneously, there are better sound absorption properties of the PU foam composites in the medium frequency region and the better value can be obtained at the lower frequency with the content of EPDM increasing. The hardness of EPDM also shows better influence on sound absorption properties, especially in the medium frequency region. It means the foam pore morphologies have influence on sound absorption properties.

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Authors and Affiliations

Wenbo Zhu
Shuming Chen
Yebin Wang
Tongtong Zhu
Yang Jiang
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Abstract

The area of environmental protection concern minimises the impact that technical objects have on the environment. Usually the most effective way of protecting the environment is to influence the source of the problem. For this reason studies are conducted to modify the construction of machines, power machines in particular, so as to minimise their impact on the environment.

In the case of environmental protection from noise it is most convenient to carry out measurements in an anechoic chamber. Unfortunately, this is possible only in very limited circumstances. In all other cases measurements are performed using an engineering method or the survey method, both of which are described in the standards and by taking into account the so-called environmental corrections. The obtained results are burdened with greater error than those of measurements in an anechoic chamber. Therefore, it would seem advantageous to develop a method of obtaining similar and reliable results as those in an anechoic chamber, but in a reverberant field. The authors decided to use numerical modelling for this purpose.

The main objective of this work is a comprehensive analysis of the numerical model of a laboratory designed for acoustic tests of selected power machines. The geometry of a room comprising an area of analysis is easy to design. The main difficulty in modelling the phenomena occurring in the analysed area can be the lack of knowing the boundary conditions. Therefore, the authors made an attempt to analyse the sensitivity of various acoustic parameters in a room in order to change these boundary conditions depending on the sound absorption coefficient

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Authors and Affiliations

Katarzyna Suder-Dębska
Ireneusz Czajka
Mateusz Czechowski
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Abstract

Efficient ultrasonic noise reduction by using enclosures requires the knowledge of absorbing properties of materials in the frequency range above 4 kHz. However, standardized methods enable determination of absorption coefficients of materials in the frequency range up to 4 kHz. For this reason, it is proposed to carry out measurements of the sound absorption properties of materials in the free field by means of a tone-burst technique in the frequency range from 4 kHz to 40 kHz at angles of incidence varying from 0° to 60°. The absorption coefficient of a material is calculated from the reflection coefficient obtained by reflecting a tone-burst from both a perfectly reflecting panel and a combination of this panel and the sample of the tested material. The tests results show that mineral wool and polyurethane open-cell foam possess very good absorbing properties in this frequency range.
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Authors and Affiliations

Dariusz Pleban
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Abstract

The cuboidal room acoustics field is modelled with the Fourier method. A combination of uniform, impedance boundary conditions imposed on walls is assumed, and they are expressed by absorption coefficient values. The absorption coefficient, in the full range of its values in the discrete form, is considered. With above assumptions, the formula for a rough estimation of the cuboidal room acoustics is derived. This approximate formula expresses the mean sound pressure level as a function of the absorption coefficient, frequency, and volume of the room separately. It is derived based on the least-squares approximation theory and it is a novelty in the cuboidal room acoustics. Theoretical considerations are illustrated via numerical calculations performed for the 3D acoustic problem. Quantitative results received with the help of the approximate formula may be a point of reference to the numerical calculations.
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Authors and Affiliations

Anna Kocan-Krawczyk
Adam Brański
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Abstract

This paper presents maps of spatial distributions of the short circuit current Isc(x,y) and the open circuit voltage Uoc(x,y) of the investigated low cost solar cells. Visible differences in values of these parameters were explained by differences in the serial and shunt resistances determined for different points of solar cells from measurements of I–V characteristics. The spectral dependence of the photo voltage of solar cell is also shown, discussed and interpreted in the model of amorphous and crystal silicon.
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Authors and Affiliations

Łukasz Bartłomiej Chrobak
Wiesław Ryszard Madej
Mirosław Andrzej Maliński
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Abstract

In order to investigate the effect of the surface shape on the performance of perforated panels, three non-flat shapes were considered for perforated panel with their absorption performance compared with the usual shape of the (flat) perforated panel. In order to simulate the absorption coefficient of a non-flat perforated panel, the finite element method was implemented by the COMSOL 5.3a software in the frequency domain. Numerical simulation results revealed that all the shapes defined in this paper improve the absorption coefficient at the mid and high frequencies. A and B shapes had a higher performance at frequencies above 800 Hz compared to the flat shape. Also, shape C had a relative superiority at all frequencies (1–2000 Hz) compared to the reference shape; this superiority is completely clear at frequencies above 800 Hz. The maximum absorption coefficient occurred within the 400–750 Hz range. After determining the best shape in terms of absorption coefficient (shape C), a perforated panel of 10 m2 using fiberglass fibers and desired structural properties was built, and then it was also subjected to a statistical absorption coefficient test in the reverberation chamber according to the standard. The results of the statistical absorption coefficient measurement showed that the highest absorption coefficient was 0.77 at the frequency of 160 Hz. Also, to compare the experimental and numerical results, these conditions were implemented in a numerical environment and the statistical absorption coefficient was calculated according to the existing relationships. A comparison of the numerical and laboratory results revealed acceptable agreement for these two methods in most frequency spectra, where the numerical method was able to predict this quantity with good accuracy.
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Authors and Affiliations

Zahra Hashemi
1
Ali Fahim
2
Mohammad Reza Monazzam
3

  1. Behbahan Faculty of Medical Sciences, Behbahan, Iran
  2. School of Engineering Science, College of Engineering, University of Tehran, Tehran, Iran
  3. School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
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Abstract

The study aims to estimate metal foam microstructure parameters for the maximum sound absorption coefficient (SAC) in the specified frequency band to obtain optimum metal foam fabrication. Lu’s theory model is utilised to calculate the SAC of metallic foams that refers to three morphological parameters: porosity, pore size, and pore opening. After Lu model validation, particle swarm optimisation (PSO) is used to optimise the parameters. The optimum values are obtained at frequencies 250 to 8000 Hz, porosity of 50 to 95%, a pore size of 0.1 to 4.5 mm, and pore opening of 0.07 to 0.98 mm. The results revealed that at frequencies above 1000 Hz, the absorption efficiency increases due to changes in the porosity, pore size, and pore opening values rather than the thickness. However, for frequencies below 2000 Hz, increasing the absorption efficiency is strongly correlated with an increase in foam thickness. The PSO is successfully used to find optimum absorption conditions, the reference for absorbent fabrication, on a frequency band 250 to 8000 Hz. The outcomes will provide an efficient tool and guideline for optimum estimation of acoustic absorbents.
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Authors and Affiliations

Rohollah Fallah Madvari
1
Mohsen Niknam Sharak
2
Mahsa Jahandideh Tehrani
3
Milad Abbasi
4

  1. Occupational Health Research Center, Department of Occupational Health Engineering, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
  2. Department of Mechanical Engineering, University of Birjand, Birjand, Iran
  3. Australian Rivers Institute, Griffith University, Queensland, Australia
  4. Social Determinants of Health Research Center, Saveh University of Medical Sciences, Saveh, Iran
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Abstract

Due to its unique features, the metal foam is considered as one of the newest acoustic absorbents. It is a navel approach determining the structural properties of sound absorbent to predict its acoustical behavior. Unfortunately, direct measurements of these parameters are often difficult. Currently, there have been acoustic models showing the relationship between absorbent morphology and sound absorption coefficient (SAC). By optimizing the effective parameters on the SAC, the maximum SAC at each frequency can be obtained. In this study, using the Benchmarking method, the model presented by Lu was validated in MATLAB coding software. Then, the local search algorithm (LSA) method was used to optimize the metal foam morphology parameters. The optimized parameters had three factors, including porosity, pore size, and metal foam pore opening size. The optimization was applied to a broad band of frequency ranging from 500 to 8000 Hz. The predicted values were in accordance with benchmark data resulted from Lu model. The optimal range of the parameters including porosity of 50 to 95%, pore size of 0.09 to 4.55 mm, and pore opening size of 0.06 to 0.4 mm were applied to obtain the highest SAC for the frequency range of 500 to 800 Hz. The optimal amount of pore opening size was 0.1 mm in most frequencies to have the highest SAC. It was concluded that the proposed method of the LSA could optimize the parameters affecting the SAC according to the Lu model. The presented method can be a reliable guide for optimizing microstructure parameters of metal foam to increase the SAC at any frequency and can be used to make optimized metal foam.

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Authors and Affiliations

Mohammad Javad Jafari
Ali Khavanin
Touraj Ebadzadeh
Mahmood Fazlali
Mohsen Niknam Sharak
Rohollah Fallah Madvari
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Abstract

Thiswork presents results of comparative studies of the optical absorption coefficient spectra of ion implanted layers in silicon. Three nondestructive and noncontact techniques were used for this purpose: spectroscopic ellipsometry (SE), modulated free carriers absorption (MFCA) and the photo thermal radiometry (PTR). Results obtained with the ellipsometric method are the proof of correctness of the results obtained with the MFCAandPTRtechniques. These techniques are usually used for investigations of recombination parameters of semiconductors. They are not used for investigations of the optical parameters of semiconductors. Optical absorption coefficient spectra of Fe+ and Ge+ high energy and dose implanted layers in silicon, obtained with the three techniques, are presented and compared.

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Authors and Affiliations

Krzysztof Dorywalski
Łukasz Chrobak
Mirosław Maliński

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