Average absorption coefficient for optically thin media

1972 ◽  
Vol 11 (1) ◽  
pp. 10-13
Author(s):  
S. P. Detkov
Keyword(s):  
Absorption Coefficient ◽  
Average Absorption Coefficient

Realizing high-efficiency low frequency sound absorption of underwater meta-structures by acoustic siphon effect

2021 ◽  
pp. 2150319
Author(s):  
Li Bo Wang ◽  
Cheng Zhi Ma ◽  
Jiu Hui Wu ◽  
Chong Rui Liu
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
High Efficiency ◽  
Physical Mechanism ◽  
Low Frequency ◽  
Area Ratio ◽  
Underwater Acoustic ◽  
Element Simulation ◽  
Average Absorption Coefficient ◽  
New Perspective

The underwater acoustic siphon effect is proposed in this work, which aims to reveal the basic physical mechanism of high-efficiency sound absorption in meta-structures composed of multiple detuned units. Furthermore, the influence of the area ratio on the underwater acoustic siphon effect is then investigated by finite element simulation (FES) and theoretical calculation. On this basis, a meta-structure with the maximum absorption coefficient of almost 100% and average absorption coefficient of 80% at 600–1400 Hz is achieved. The underwater acoustic siphon effect could provide a better understanding of high-efficiency sound absorption and offer a new perspective in controlling underwater noises.

Preliminary Study on Bamboo as Sound Absorber

2014 ◽  
Vol 554 ◽  
pp. 76-80 ◽  
Author(s):  
Fazlin A. Khair ◽  
Azma Putra ◽  
Mohd Jailani Mohd Nor ◽  
Nurul Atiqah ◽  
M.Z. Selamat
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Hollow Structure ◽  
Chemical Substance ◽  
The Body ◽  
Natural Material ◽  
Sound Absorber ◽  
Tube Test ◽  
Average Absorption Coefficient ◽  
Preliminary Study

Synthetic acoustic materials are known for their poisonous chemical substance to the environment and also the particles which are harmful to human health. Research is now directed towards finding an alternative acoustic absorber made from natural materials. This paper presents the utilization of bamboo, a natural material having hollow structure to act as sound absorber. In an impedance tube test, the hollow path is arranged to face the sound incidence. The result reveals that bamboo having length of 2 cm has average absorption coefficient of 0.95 at frequency above 3 kHz. Performance at lower frequencies can be controlled by adding the air gap behind the system. Introduction of microholes along the body shows no significant effect to increase the sound absorption.

Emissivity Calculations for Diatomic Gases

1951 ◽  
Vol 18 (1) ◽  
pp. 53-58
Author(s):  
S. S. Penner
Keyword(s):  
Absorption Coefficient ◽  
Atmospheric Pressure ◽  
Radiant Heat ◽  
Published Data ◽  
Radiant Heat Transfer ◽  
Effective Width ◽  
Combustion Chambers ◽  
Average Absorption Coefficient ◽  
Vibration Rotation ◽  
Simplified Procedure

Abstract An approximate method for estimating radiant-heat transfer from gaseous emitters has been developed. An average absorption coefficient is used for an effective width of an entire vibration-rotation band. The procedure for determining an average absorption coefficient in terms of integrated absorption can be justified, approximately, for very large total pressures where the spectral half-width is no longer small compared with the rotational spacing. Because of this limitation, it is to be expected that the procedure proposed here will be particularly useful only in estimating gaseous emissivities for emitters in high-pressure combustion chambers. Nevertheless, it appears that the simplified procedure yields reasonable results even at relatively low total pressures. Thus a comparison of calculated and observed emissivities for CO at atmospheric pressure shows satisfactory agreement, especially at large optical densities. Representative emissivity calculations over a wide temperature range are described. Emissivity calculations on CO, NO, HF, HCl, HBr, and HI can be carried out very rapidly by the use of recently published data on these gases.

Utilizing Hollow-Structured Bamboo as Natural Sound Absorber

2015 ◽  
Vol 40 (4) ◽  
pp. 601-608 ◽  
Author(s):  
Azma Putra ◽  
Fazlin Abd Khair ◽  
Mohd Jailani Mohd Nor
Keyword(s):  
Absorption Coefficient ◽  
Hollow Structure ◽  
Front Surface ◽  
Normal Incidence ◽  
Frequency Range ◽  
Peak Absorption ◽  
Natural Sound ◽  
Average Absorption Coefficient ◽  
Lower Frequency Range ◽  
Bamboo Structure

AbstractStudies 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.

Preparation and Performance of Porous Silica of Sound-Absorbing Coating

2012 ◽  
Vol 568 ◽  
pp. 307-310 ◽  
Author(s):  
Jin Chen ◽  
Xiao Gang Wang ◽  
Min Zhang ◽  
Ai Xia Guo ◽  
Lei Tang
Keyword(s):  
Wear Resistance ◽  
Acrylic Acid ◽  
Absorption Coefficient ◽  
Acid Ester ◽  
Sound Absorption ◽  
Porous Silica ◽  
Curing Agent ◽  
Absorption Properties ◽  
Average Absorption Coefficient ◽  
And Performance

Using the poly-acrylic acid ester modified porous silica as fillers, the E-44 epoxy resin as matrix, ethylene diamine as curing agent prepared the sound absorption coating, and the sound absorption properties of and wear resistance were tested. The results showed that: the coating wear resistance increased with the addition of filler increasing，and then decreased. The wear mass of 60%filler coating is the lowest. The absorption coefficient increases with the filler increasing, the average absorption coefficient can reach 0.22 of 1000Hz frequency sound.

Mathematical Modeling of In-Cylinder Radiation

2012 ◽  
Vol 482-484 ◽  
pp. 2345-2349
Author(s):  
Hong Yan Chen ◽  
Yi Jin Song
Keyword(s):  
Mathematical Modeling ◽  
Absorption Coefficient ◽  
Working Conditions ◽  
Combustion Engine ◽  
Total Carbon ◽  
Carbon Particles ◽  
Oxidized Carbon ◽  
Average Absorption Coefficient ◽  
Radiant Temperature

This paper develops a multi-zone & multi-dimensional in-cylinder radiant model for internal-combustion engine. The model is based on the radiant temperature formula and takes the quality of total carbon particles and oxidized carbon particles as weight.The model offers analysis of the tendency of average absorption coefficient in various zones under different working conditions. The result agrees with basic characters about radiation.

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