Absorption Coefficient Of Material Research Articles

On the development of a virtual test bench to assess sound absorption of materials in an alpha chamber

A description is given of a virtual test-bench (VTB) designed by engineering center of Peter the Great St. Petersburg Polytechnic University to calculate a sound absorption coefficient of various materials. Developed VTB differs from known programs in that it allows a sound absorption coefficient of various materials to be determined with minimum involvement of an engineer. This VTB differs from other programs also by using infinite elements jointly with finite elements, which increases adequacy of the discrete model being used, and also the configuration of the boundary of an alpha chamber being used. The known programs use various phenomenological mathematical models of porous materials such as Johnson-Champoux-Allard (JCA) model. The VTB is based on fundamental mathematical models and statistical energy analysis (SEA) that allow describing adequately the established or transitional processes of sound absorption and reflection by a porous material the properties of which are not homogenized. The value of this VTB, which is created on the basis of a VA One software complex supplemented by a set of files of boundary conditions, files of solvers’ settings, secondary finite element (FE) models, is that VTB allows standardized calculations to be performed to determine the sound absorption coefficient of a material with minimum involvement of an engineer and the obtained result to be submitted for detailed processing. Developed virtual test-bench enables determination of a sound absorption coefficient for various materials within the entire finite frequency range. The result of the calculation is displayed as a graph of dependency of the material sound absorption coefficient on frequency.

Predicting Model of Sound Absorbing Properties of Cellulose-based Porous Materials Prepared by Foam Forming

ABSTRACT Cellulose-based porous materials with a three-dimensional network skeleton and sound-absorbing properties prepared by foam forming were successfully made in this study. A refitted empirical model based on the Delany-Bazley model had been developed to predict the sound absorption coefficient of cellulose-based porous materials. The parameters of the model had been adjusted to best fit the values of flow resistance rate and sound absorption coefficient measured by the double-thickness method. The results showed that the average error of the fitted model between 200 and 6300 Hz was only 3.2%, indicating that the new model could predict the basic acoustic properties of cellulose-based porous materials with a measured flow resistance rate.

Study on the influence of sample size and test conditions on the capillary water absorption coefficient of porous building materials

Capillary water absorption coefficient is one of the important wet parameters that characterize the liquid water absorption capacity of porous building materials. Relevant standards uniformly stipulate the size and test conditions of the specimen in analysis of this hygrothermal parameter for porous building materials. However, different porous building materials have different water absorption capabilities due to their pore structures. Therefore, the use of the same test conditions or standards when obtaining the capillary water absorption coefficient of the material will affect the accuracy of the obtained results. In this paper, an experiment with capillary water absorption was performed to study the influence of sample size, ambient temperature and water immersion depth on the capillary water absorption coefficient of foamed cement (FC), aerated concrete (AAC) and coral sand concrete (SHS) with different pore structures. The results show that the sample size and the depth of water immersion have a significant influence on the capillary water absorption coefficient value of FC; the ambient temperature has a significant influence on the capillary water absorption coefficient value of AAC. When temperature increases from 5°C to 35°C, the growth rate of the AAC capillary water absorption coefficient is about 71.3%. The depth of water immersion significantly affects the capillary water absorption coefficient value of the SHS. When the depth of water immersion increases from 3 mm to 10 mm, the growth rate of the SHS capillary water absorption coefficient is about 38.4%. ∙ Analyze the water absorption process of different pore materials. ∙Analyze the data processing method of capillary water absorption coefficient in different water absorption processes of materials. ∙Analyze the influence of sample size, ambient temperature, and water immersion depth on the capillary water absorption coefficient of different pore materials. ∙Weight analysis of factors affecting the capillary water absorption coefficient of different porous building materials. ∙Provide sample size, ambient temperature, water immersion depth and other experimental conditions and data processing methods for the determination of the capillary water absorption coefficient of different porous building materials.

Heating of carbonaceous materials: Insights into the effects of thermal metamorphism on spectral properties of carbonaceous chondrites and asteroids

AbstractCarbonaceous chondrites (CCs) are important materials for understanding the early evolution of the solar system and delivery of organic material to the early Earth. Spectral analysis of CCs can establish the relationship between them and their possible parent asteroids, which helps to determine the surface composition of the asteroid. In this paper, the 0.3–26 μm reflectance spectra of a series of coals ranging from lignite to anthracite (Earth analogs of organic matter contained in CCs), a coal heated to various durations and temperatures, and reflectance spectra of CM2 meteorites were analyzed in conjunction with compositional information to derive spectral–compositional relationships. All types of coals have strong aromatic absorptions (3.28 and 5–6.5 μm) and aliphatic “triplet” absorptions (3.38, 3.41, and 3.48 μm). In contrast, CM2 meteorites have obvious aliphatic absorptions and lack aromatic absorptions. The reason is the weak absorption coefficients of aromatic materials and the overlap with strong OH/H2O absorption. Absorptions in the coal spectra are strongly related to elemental H/C ratio. When the H/C ratio is >0.55, the absorption intensity of an aliphatic increases linearly with the increase of H/C. For heated coal, increasing heating time above 1 h at 450 °C causes the disappearance of the aliphatic “triplet” absorptions. Similarly, heating Murchison meteorite to 400 °C for 1 week causes all the organic absorptions to disappear. This implies that in remote sensing detections, only asteroids (e.g., with CM and CI carbonaceous chondrites compositions) that experienced low thermal metamorphism (<400 °C) are suitable as potential targets for detecting organic compounds using features in the 3–4 µm region.

Acoustic Parameters of Classrooms in Akwa Ibom State, South-South Nigeria

It has been proven that acoustic conditions in classrooms have great influence on the performance of students and give stress to the teachers. Long reverberation time may also deteriorate speech quality by reducing the signal to noise ratio (SNR). This work aimed at predicting the absorption “ a” and thereby calculating the reverberation time of some classrooms in Akwa Ibom State, South-South Nigeria using simple Sabin equations and to make appropriate recommendations where they fall short of the recommended standard of 0.75 to 1.00 seconds for classrooms and lecture halls. Effective absorption coefficients of materials used for the construction of the classrooms under study were used for the calculation of the absorption of these classrooms while the Sabin equation was used to calculate the reverberation time. The results show that all the classrooms under study which were representatives of the classrooms in the area of study had reverberation time that were within the recommendation time of 0.75 to 1.00 seconds. The classrooms in the area of study could be certified to be good for lecture delivery by the teachers , good speech intelligibility and lecture assimilation of the students. Keywords: Absorption coefficient, Absorption, Reverberation time, Speech intelligibility DOI: 10.7176/JEES/11-9-05 Publication date: September 30 th 2021

A hybrid method of predicting the acoustical properties of multi-layered materials

Many numerical and measuring approaches are widely used in predicting and analysing the acoustic performances of laminated materials for noise control applications. However, numerical methods generally require a set of non-acoustic parameters, and the measuring methods are not available for exceedingly thick materials. The main aim of this article is to address a hybrid approach of evaluating the normal incidence sound transmission loss and absorption coefficients of multi-layered materials. This method is performed with some special parameters that contain the sound transmission and reflection coefficients of each sub-layer of a multi-layer specimen and can be measured by a standing wave tube system. The accuracy and feasibility of the present method are validated by the experimental and numerical comparisons between different methods and samples. Moreover, this present approach can be applied as a numerical tool of estimating the acoustical behaviours of multi-layered structures in noise control treatments, such as automotive, building and aerospace industries.

Measuring the absorption coefficient of optical materials with arbitrary shape or distribution within an integrating sphere.

The absorption coefficient of a material is classically determined by measuring the transmittance of a homogeneous sample contained within flat optical faces and under collimated illumination. For arbitrary shapes this method is impracticable. The characterization of inhomogeneous or randomly distributed samples such as granules, powders or fibers suffers the same problem. Alternatively, an integrating cavity permits us to illuminate a sample under a homogenous and isotropic light field where the analysis simplifies. We revisit this strategy and present a new formal basis based on simple radiometric laws and principles. We introduce a new concept to describe the absorption: the optical form factor. We tackle a rigorous treatment of several regular forms, including full absorption range and the reflection at its surfaces. We also model and improve an integrating sphere setup to perform reliable measurements. Altogether, it permits achieving simple but general conclusions for samples with arbitrary shape or spatial distribution, from weak to highly absorbing, expanding the applicability of quantitative absorption spectroscopy. Finally, we validate it by measuring different sample formats made of PMMA: a cube, groups of granules and injection molding loose parts. The absorption coefficient of PMMA varies near three orders of magnitude in the explored range (380-1650 nm).

Broadband multimodal THz waveguides for efficient transfer of high-power radiation in space-confined conditions

Terahertz (THz) range, which lies between the microwave and infrared regions of the electromagnetic spectrum, presents a new frontier containing an abundance of technical applications and fundamental research problems. There are several challenges limiting the progress in the THz science and technology. One of them is the limited range ofthe guided-wave propagation of THz radiation, owing to the high loss from the finite conductivity of metals and the high absorption coefficient of dielectric materials in the THz range. In this work, we discuss the design and fabrication of multimodal hollow THz waveguides used at the X-band Electron Paramagnetic Resonance (EPR) endstation located at the Novosibirsk Free Electron Laser facility (NovoFEL). Experiments carried out at the EPR endstation are aimed to investigate the impact of THz and far infrared radiation on the spin system of different inorganic complexes and organic radicals. The EPR probehead and cryostat impose strict constraints on the possible ways of transferring the THz radiation to the sample, requiring the development, manufacturing, and characterization of specific waveguides. The proposed waveguides for X-band EPR measurements under THz radiation resemble hollow metal/dielectric waveguides. They have the shape of ahollow cylinder, tapering towards the end, with a silver-coated inner surface, and allow THz radiation to be transmitted over a distance of about 60 cm in a wide frequency range from THz to middle infrared. The waveguides performance was characterized at different frequencies of NovoFEL radiation and compared with numerical simulations. Following the requirements ofpolarization-sensitive EPR experiments, the waveguides were further modified by a miniature attachment, consisting of a polarizer, a semiconductor mirror, and a quarter-wave plate. The attachment allows preserving the initial polarization properties of THz radiation, turns its propagation vector, and creates the circular-polarized light irradiating the sample – all inside the limited volume of the EPR probehead.

Application of equivalent diameter in sound absorption performance prediction of non-circular sectional polyester fibers

Polyester fiber as good sound absorber is used widely in various scenario. But there are few researches on model prediction of sound absorption property for the polyester fiber with non-circular cross-section. Polyester samples made from circle, triangle, flat, and cross cross-sectional fiber were prepared under different bulk densities separately in this study. Their airflow resistance values and sound absorption coefficients with 50 mm air cavity were measured. The equivalent diameters were acquired by analytical inverse method. Johnson-Champoux-Allard (JCA) model was adopted with the equivalent diameter to calculate the sound absorption coefficient of non-circular polyester fiber material. The results showed that sound absorption performance of non-circular fiber was higher than that of circular one at the similar bulk density before airflow resistance critical value. The equivalent diameters of non-circular fibers were less than circular one. Sound absorption coefficients obtained by the equivalent diameters (about 10 μm) were in good agreement with the experimental values. But to guarantee calculation accuracy, the equivalent method should be applied in the case of airflow resistance less than 100,000 Pa·s/m2.

Investigation of Acoustic Properties of Poroelastic Asphalt Mixtures in Laboratory and Field Conditions.

Measures for the improvement of acoustic conditions in the vicinity of roads include the construction of pavement structures with low-noise surfaces with optimal macrotexture and the highest possible sound absorption coefficient. Laboratory evaluation of acoustic properties of a designed asphalt mixture before its placement in the pavement is a good solution. Currently, the most popular method for the determination of the sound absorption coefficient of various construction materials under laboratory conditions is the Kundt’s tube test. Sound absorption coefficient can also be assessed based on field and laboratory measurements performed using a Spectronics ACUPAVE System. Other parameters characterising the acoustic properties of road pavement courses include air void content and water drainability or permeability. The article presents an analysis of results of sound absorption coefficient obtained using a Spectronics ACUPAVE System and water drainability and permeability of poroelastic mixtures obtained both in laboratory and on test sections, in relation to air void content and grading of the mixtures. It was established that poroelastic mixtures containing an aggregate of maximum particle size of 5 mm are characterised by better acoustic properties than mixtures with a maximum aggregate particle size of 8 mm. Changes of crumb rubber aggregate grading and bitumen type (within the tested range of values) as well as the addition of lime have shown no evident influence on the sound absorption coefficient. Noise level values at the speed of 30 km/h according to the CPX method were measured as well. Relationships between sound absorption coefficient, water drainability/permeability, and air void content were determined. The performed analyses confirmed that Spectronics ACUPAVE System may be applied for evaluation of acoustic properties of asphalt mixtures in laboratory conditions, but further research is needed to reduce the uncertainty of the results.

Research on Influencing Factors of Sound Absorption Coefficient in Reverberation Chamber

<div class="section abstract"><div class="htmlview paragraph">In the automotive industry, testing the sound absorption coefficient of acoustic materials through reverberation chambers has been widely used. The advantage of this method is that sound waves are incident on the surface of acoustic materials randomly, which is more in line with actual engineering. At present, most of the reverberation chamber design and construction refers to the international standard ISO 354-2003. However, although the design indicators of the reverberation chamber have already met the requirements of the standard ISO 354-2003, there are still some differences between the test results of different reverberation chambers on the same group of samples to be tested, and sometimes the differences are so big they affect the engineering applications. In this paper, the sound absorption coefficients of the same group of samples in different reverberation chambers are tested, and there are some differences in the sound absorption coefficients. Also, the sound absorption coefficients of a variety of samples of different materials in several different reverberation chambers were tested, confirming that there is a phenomenon of poor repeatability of the sound absorption coefficient of the reverberation chamber test. To optimize the poor repeatability of the sound absorption coefficient of the reverberation chamber test, the diffuser in a reverberation chamber is arranged in many different ways. In each reverberation chamber with a different layout, the sound absorption coefficient of the same piece is tested. The diffuser layout of the reverberation chamber was adjusted to the optimal arrangement according to the test results of the sound absorption coefficient. Next, each factor in the testing process of the sound absorption coefficient that may have an impact on the test results is examined separately, and the influencing factors are analyzed. Finally, the optimal test scheme for testing the sound absorption coefficient in the reverberation chamber is given. More importantly, an acceptable margin of error is given regarding the sound absorption coefficient of the reverberation chamber test material.</div></div>

Transient thermal model of nanosecond pulsed laser ablation: Effect of heat accumulation during processing of semi-transparent ceramics

Nanosecond ablation of semi-transparent ceramics represents a particularly interesting scenario where non-linear absorption mechanism allows absorption of laser energy for photon energy below the band gap of the material. Yttria Stabilized Zirconia (YSZ) ablated by infrared radiation represents as an example of such scenario. Ablation threshold experiments reveal a stark difference between the behaviour observed during ablation of single pulses compared to multiple pulses. During single pulses, a statistical occurrence of ablation is observed. For laser intensity below the dielectric breakdown threshold, this phenomenon has been explained on the basis of a defect-mediated thermal runaway which causes an exponential increase of the bulk material absorption coefficient as function of temperature. To investigate this phenomenon, and its effect during multi-pulse ablation, a 1D modelling framework has been developed and validated. The framework focuses on simulation of ablation of trenches (i.e. partially overlapped pulses) considered as convolution of single pulses, and account for the governing equation of heat diffusion, vaporization, plasma shielding, volumetric absorption and temperature-dependent absorption coefficient by use of a simplified defect mediated absorption model which represents the main novelty of the paper.The application of the model for various laser processing parameters reveals the importance of heat accumulation on the process. A positive feedback mechanism is established over successive pulses which leads to the material becoming progressively more absorbing, and eventually results in material removal through ablation. This phenomenon explains the sharp ablation threshold observed experimentally during ablation of trenches. The modelling framework also reveals interesting dynamics caused by the temperature dependence of the material absorption behaviour, such as a delay in the starting time for material removal, and drastic changes in the energy distribution within the sample throughout the duration of a laser pulse.Ultimately, the effect of heat conservation, which is often neglected, has been shown to represent a key dynamic during multi-pulse ablation, and should be accounted for during simulations of real-world laser processes, in particular for low diffusivity semi-transparent materials.

Improving the Sound Absorption of Natural Waste Material-based Sound Absorbers Using Micro-perforated Plates

ABSTRACT Both natural and synthetic fibers do not perform well at low frequencies and are also subjected to erosion, moisture, fire, etc., when used as an interior finish of room walls. To overcome these problems, micro-perforated plate with different thickness is used in a multilayer sound absorber configuration to improve its sound absorption. Firstly, the acoustic properties of five natural wastes including sheep wool, goat wool, camel wool as well as pith and fiber bundles of sugarcane bagasse were determined by using an impedance tube following ISO 10534–2. Secondly, the effect of Panel thickness was investigated. The maximum sound absorption coefficient (SAC) of natural waste materials is at middle to high-frequency range and this shifted to lower frequency as the porous layer thickness increases. The sound absorption performance depends on the thickness of perforated plate and porous layer in a compound sound absorber. It is observed that the using perforated plate in the front of low thickness porous materials significantly improve the SAC and absorption bandwidth. However, it should be noted that this reduces the SAC at high frequencies. Accordingly, the thick micro-perforated panels backed by porous layer are not recommended to control sounds with frequency higher than 3000 Hz.

Marble Powder Blended Utilization Polyurethane as Soundproof Materials

As technology advances, the development of equipment used by humans is increasing and most of the equipment produces unwanted sounds that cause noise. To overcome this, an alternative material for soundproofing is needed which is relatively cheap and easily available in the community by using marble powder as a polyurethane mixture in soundproof panels. The purpose of this study was to determine the effect of the sound absorption coefficient value and to determine the relationship between the frequency of the sound source and the sound absorption coefficient of acoustic materials using marble powder mixed with polyurethane in different compositions. The sound absorption test in this study was carried out using a two-microphone impedance tube and has a frequency limit of 125 Hz - 4000 Hz, variations in the mass composition of marble and polyurethane powder 1: 1, 1: 2 and 1: 3 with a thickness of 5 cm, 3cm and 1 cm. Then the test results of the 1: 1 test specimen, the lowest sound absorption coefficient value was obtained 0.10 0.73 cm-1 at a thickness of 1 cm with a frequency of 4000 Hz and the highest was 0.73 cm-1 at a thickness of 5 cm with a frequency of 125 Hz, the test results 1: 2 test specimen, the lowest sound absorption coefficient value is 0.29 cm-1 at a thickness of 5 cm at a frequency of 4000 Hz and the highest is 0.67 cm-1 at a thickness of 5 cm at 250 Hz, then the test results of the test specimen are 1: 3 values The lowest sound absorption coefficient was 0.24 at a thickness of 1 cm at a frequency of 4000 Hz and the highest was 0.71 at a thickness of 5 cm at a frequency of 250 Hz. For the comparison of the sound absorption coefficient values ​​based on the composition and thickness, the lowest and highest sound absorption coefficient values ​​are found in 1: 1 specimens with a thickness of 1 cm and 5 cm with the best sound absorption coefficient values ​​on average at a frequency of 500 Hz, but in material 1:2 and 1:3 obtained the sound absorption coefficient values ​​are in between on the grounds that the thicker the material, the higher the sound absorption coefficient value. Thus it can be concluded that the polyurethane composite material mixed with marble powder can be used as a sound absorbing panel material, especially in a 1: 1 composition

Spectral Absorption Coefficient of Additive Manufacturing Materials

Abstract Active thermography techniques are of interest for quality assurance of additive manufacturing processes. However, accurate measurements of thermophysical properties of materials are required to successfully implement active thermography. In particular, the spectral absorption coefficient of materials commonly used in additive manufacturing must be known to accurately predict the spatial distribution of thermal energy generated from absorption of power emitted by a laser or pulsed flash lamp. Accurate measurements of these optical properties are also needed to develop greater understanding of additive manufacturing processes that rely on radiative heat transfer to fuse powders. This paper presents spectral absorption coefficient measurements and uncertainty estimates of fully and partially dense ABS, PLA, and Polyamide 12 samples.

Design and simulation of multilayer hybrid foam material for acoustic application

New acoustic multilayer absorber fabricated by coupling closed-cell metallic foam and open-cell polymeric foam, which aimed to develop a practical use of metallic foam in the noise control application. In prior, the individual sound absorption coefficient of both foam materials with different thicknesses measured by the impedance tube method as per ASTM E-1050. Using inverse characterization technique, the intrinsic properties needed for five parameter models in a numerical study are predicted. The measured characteristic impedance, complex wave propagation, and sound absorption coefficient of the individual foams are in close agreement with the prediction. Subsequently, a different configuration of multilayer absorber is modeled using obtained properties, and their acoustic performance is evaluated. The result indicates that the coupling of polymeric foam with metallic one exhibits enhanced sound absorption and usage of closed-cell metallic foam in noise control material. Furthermore, the result demonstrates that absorption capability entirely relies on the placement of polymeric foam in the configuration. The proposed hybrid multilayer absorber coupled with test bench car for interior acoustic study, where 5–30 dB is reduction is noticed in 1/3rd octave plot.

Sound absorption coefficients of porous sound absorbing materials composed of two types of fibers with different diameters

Sound absorption coefficients of porous sound absorbing materials composed of two types of fibers with different diameters

Numerical Simulation for the Sound Absorption Properties of Ceramic Resonators

This work reports the results of experimental measurements of the sound absorption coefficient of ceramic materials using the principle of acoustic resonators. Subsequently, the values obtained from the measurements were used to train a simulation model of the acoustic behavior of the analyzed material based on artificial neural networks. The possible applications of sound-absorbing materials made with ceramic can derive from aesthetic or architectural needs or from functional needs, as ceramic is a fireproof material resistant to high temperatures. The results returned by the simulation model based on the artificial neural networks algorithm are particularly significant. This result suggests the adoption of this technology to find the finest possible configuration that allows the best sound absorption performance of the material.

Dynamic flow resistivity and sound absorption of compressed fibrous porous materials: Experimental and theoretical

Fibrous porous materials are the preferred absorbers for many applications since they can absorb impact energy and sound waves. The microscopic morphology and the relationship between the compressed state and sound absorption characteristics are studied for compressed fibrous porous materials. A series of specimens of fibrous porous materials are prepared and compressed to different thicknesses, and their pore size distributions are analyzed. The average pore size, dynamic flow resistivity, and acoustic impedance of the compressed fibrous porous materials are derived theoretically. The effects of porosity, thickness, average pore size, compression ratio, and combinations of these parameters on the dynamic flow resistivity and sound absorption coefficient of compressed fibrous porous materials are discussed theoretically. It is demonstrated that the compression ratio decreases the sound absorption coefficient of fibrous porous materials. The compression ratio and average pore size are important factors for the dynamic flow resistivity and sound absorption coefficient. Our results could help establish a theoretical foundation for understanding the microscopic morphology of compressed fibrous porous materials and aid the design of fibrous porous materials for various applications.

Investigations on Structural, Mechanical, Optical, Electrical, Third-Order Nonlinear Optical and Antibacterial Activity of 4-Aminopyridine Monophthalate Single Crystal

An organic 4-aminopyridine monophthalate (PA4AP) single crystal grown by solvent evaporation at room temperature was studied for third-order nonlinear optical and antibacterial applications. The title material was found to crystallize in a non-centrosymmetric orthorhombic system with space group P212121, and the crystallographic information was acquired by its response to X-ray diffraction analysis. The functional groups and their different modes of vibration were studied by FTIR spectroscopy to identify the various chemical bonds present in PA4AP. Optical absorption study revealed less absorption in the visible region with an absorption cut-off wavelength at 315 nm, below which the material shows complete absorption. The title crystal was characterized for luminescence and based on this the inter-band structures were analysed for crystal defects. Mechanical and dielectric properties with an emphasis on solid-state parameters were investigated to understand the crystal stability for device applications. Kurtz–Perry powder analysis revealed that the PA4AP crystal has comparable second harmonic generation efficiency with the well-known KDP crystal. The third-order nonlinear optical susceptibility (χ(3)), nonlinear absorption coefficient (β) and nonlinear refractive index (n2) of title material were found to be 1.06 × 10−6 (esu), 6.51 × 10−5 (cm W−1) and 2.33 × 10−8 (cm2 W−1), respectively. The reverse saturable absorption observed in open aperture Z-scan indicates the suitability of PA4AP for optical limiting application. The antibacterial activity was investigated against few foodborne pathogens which show the antibacterial stability of PA4AP against Shigella flexneri and Vibrio cholerae bacteria.