• Journal of the Optical Society of Korea
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• 제13권2호
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• pp.261-266
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• 2009

The angular dispersion-type non-scanning Fabry-Perot was applied to an ethanol-water mixture in order to investigate its acoustic properties such as the sound velocity and the absorption coefficient. The scattered light from the mixture was analyzed by using the charge-coupled-device area detector, which made the measurement time much shorter than that obtained by using the conventional scanning tandem multi-pass Fabry-Perot interferometer. The sound velocity showed a deviation from ultrasonic sound velocities at low temperatures accompanied by the increase in the absorption coefficient, indicating acoustic dispersion due to the coupling between the acoustic waves and some relaxation process. Based on a simplified viscoelastic theory, the temperature dependence of the relaxation time was obtained. The addition of water molecules to ethanol reduced the relaxation time, consistent with dielectric measurements. The present study showed that the angular dispersion-type Fabry-Perot interferometer combined with an area detector could be a very powerful tool in the real-time monitoring of the acoustic properties of condensed matter.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1347-1352
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• 2001

In this study, the acoustic properties of polyester sound absorbing materials with three different bulk densities were investigated by calculating and measuring the acoustic parameters in terms of characteristic impedance, propagation constant, and absorption coefficient. For the calculations, Delany and Bazley's empirical equation was used together with the experimentally obtained specific flow resistivities under steady flow conditions. For the experimental measurements, the well-known two-thickness method was accessed. The experimentally measured values of characteristic impedance and propagation constant were generally agreed well with the corresponding calculated values. Based on the comparisons between the calculations and measurements, it was found that the magnitude of the absorption coefficient was closely related to the characteristic impedance and the real part of the propagation constant. Especially, the maximum magnitude of the absorption coefficient was depended upon the imaginary part of the propagation constant indicating the phase change of the propagation constant.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.935-940
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• 2001

This study search for absorbing sound and exhaust-gas which aims to manufacture continuous void by using clay and foam, the surface of materials is covered with $TiO_{2}$ powder as heat treatment. According to the results of the experiment, the increase of thickness of manufactured sound absorbing materials caused the increase of absorption rate in the range of low and middle sound and thus it can be an important factor of improving absorption rate. Sound absorbing materials could satisfy 70% of the average of sound absorption ratio in 7cm thickness. Also, the manufactured sound absorbing materials is covered with $TiO_{2}$ showed an excellency in the clarification of exhaust-gas under ultraviolet rays treatment when 70% of removal rate and about 10% of generation rate of $NO_{2}$ is settled by the flow of 2 $\ell$/min NO gas. Especially, manufactured sound absorbing materials could improve compressive strength of continuos porous concrete. in the case of 7% bubble addition, when the substitution rate of coagulator was 30% and 20%, compressive strength was 45kgf/$cm^{2}$ and 65kgf/$cm^{2}$ respectively. As the substitution rate of coagulator reducing, compressive strength increased after preforming burnt clay.

• The Journal of the Acoustical Society of Korea
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• 제21권2E호
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• pp.81-90
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• 2002

Single absorbing materials and Helmholtz resonators have limited absorption characteristics over limited frequency ranges due to their structures and properties. Porous materials are highly absorptive for mid and high frequency ranges, while they have little sound absorption for low frequency sounds. Helmholtz resonators are generally used to absorb sound energy for a specified frequency range. Hence they have limited capability in controlling the overall acoustic properties of a space. Not much has been known about useful finishing materials which have enough rigidity and absorption over broad frequency range, in spite of wide demands from acoustic designers and consultants. The present work measured and analyzed absorption characteristics of a slit absorber by varying surface materials, depths of air gap, dimensions of slat and slit widths. It was found that the narrower the slit width, the larger the absorptions over the wide frequency ranges and the pattern was dependent on the presence of porous material. Narrower slat's width tend to increase the slit absorber's absorption more or less. Absorption coefficients at low frequency ranges were dramatically improved (from 0.23 to 0.56) by increasing air gap when porous materials were present.

• 수산해양기술연구
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• 제48권2호
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• pp.174-179
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• 2012

A new absorption material, cellulose sponge soaked in cement, was made for anechoic water tank and its acoustical properties were investigated by pulse methods. The sound absorption coefficient a (dB/cm) of the material was obtained in the frequency range of 40~120kHz from the echo reduction ER (dB) and insertion loss IL (dB) data. The result was averagely 1.8dB/cm higher than the sound absorption coefficient a (dB/cm) of cork-filled rubber which is one of the most effective absorption materials. The wedge (1.2~5.0cm long) type absorption tiles were made with this new material. The echo reduction ER (dB) of the absorption tile with 5.0cm wedge measured in water tank was higher than 20dB in the experimental frequency range.

• 한국소음진동공학회논문집
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• 제24권7호
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• pp.562-568
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• 2014

This study aimed to identify changes in the physical properties of artificial mineral-fiber materials used as building insulation that had been installed in the outer walls of buildings for a long time. To achieve this goal, glass fiber and rock wool were collected from outer walls in actual buildings and their acoustic and thermal performances were measured. These were compared with measurements from similar products manufactured recently. The results showed that old, used samples had a lower sound absorption coefficient compared to recently manufactured materials. The old samples also displayed increased compressibility compared to new materials. For example, the compressibility difference for glass wool was 7.32 mm. Old samples had a dynamic stiffness $1.28MN/m^3$ higher than new material samples. The thermal conductivity of both old and new samples increased within creasing temperature. They showed similar results at temperatures between 0 and $20^{\circ}C$.

• Journal of the Korean Wood Science and Technology
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• 제51권6호
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• pp.470-480
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• 2023

This study aimed to develop a sound-absorbing composite using sugarcane bagasse (SB) and coffee silver skin (CS) as raw materials. The composite boards were manufactured by bonding the fibers with Melamine Urea-Formaldehyde adhesive, ensuring a consistent thickness of 30 mm. Various densities were employed, namely 380, 450, and 520 kg/m³. The samples were fabricated with different fiber ratios, including SB100%, SB75% with CS25%, and SB50% with CS50%. The sound absorption coefficient (SAC) and noise reduction coefficient (NRC) were measured using the impedance tube method within a frequency range of 63-6,300 Hz. The experimental results revealed that the mixing ratio of CS exerted a notable influence on enhancing the SAC, while the density of the composite board exhibited a significant impact on increasing both the SAC and NRC. Among the densities tested, the optimal value was observed at 520 kg/m³, yielding a SAC value of 0.65 at a frequency of 1,000 Hz and an NRC value of 0.55 for the SB50-CS50 composite plate. These findings underscore the importance of considering the CS mixing ratio and composite board density when aiming to optimize sound absorption properties.

• 소음진동
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• 제10권5호
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• pp.892-897
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• 2000

In this paper, experimental methods to find acoustic characteristics of acoustically treated air-conditioning duct system are proposed. Existing methods to analyze acoustic properties of duct with absorbent material have dilemma which has to assume the wave in duct to be a plane wave. Under this assumption. applicable frequency limitation makes accurate analysis of practical air-conditioning system impossible. In order to analyze the properties of in-lined treated absorbent with high degree of accuracy, in this experiments the range of exciting frequency of sound source is broadband, which means that source speaker excited higher mode of in-duct sound field. Also, to define the relations of air cavity to the acoustic characteristics, acoustic experiments on ducts with air cavity of different depth are operated. In conclusion, air-cavity makes the absorbing ability of duct improved in low frequency range. Due to the interactions between the air cavity depth and the depth of absorbents, according to depth of cavity, the magnitude of absorption coefficients vs frequencies in specific range is changed. In lower frequency range, the absorption of sound energy by air cavity is more dominant than by absorbent itself, in higher range, the inversion is true.

• 콘크리트학회논문집
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• 제20권5호
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• pp.653-660
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• 2008

본 연구는 펄라이트를 이용한 흡음재료의 흡음성능을 개선시키기 위한 최적배합에 대한 분석을 실시하였다. 결합재로서 폴리머 시멘트 슬러리와 무기질 결합재를 사용하여 흡음재료를 각종 배합조건에 따라 제작하여, 강도, 동결 융해 저항성, 그리고 흡음성능에 대하여 실험을 실시하였다. 실험 결과, 관내법에 의한 흠음재의 흠음계수는 배합에 따라 약간의 차이가 있으나 폴리머 디스퍼션을 결합재로 사용한 경우 흡음재의 감음계수 (NRC)는 $0.48{\sim}0.51$로 시멘트만 결합재로 사용한 경우에 비해 약간 크게 나타났으나, 방음벽의 환경부 고시 기준에서의 흡음재로서 감음계수 0.70에 비하면 낮은 수치이다. 그러나 잔향실법에 의한 흡음용 패널의 저주파수 영역($250\;Hz{\sim}500\;Hz$)에서 흡음계수가 $0.84{\sim}1.00$로 매우 높게 나타났으며, 고주파 영역에서도 $0.57{\sim}0.77$ 정도로 비교적 높은 흡음률을 나타내 감음계수가 0.77로 높게 나타났다. 폴리머 디스퍼션을 결합재로 사용한 흡음재는 압축강도, 휨강도 및 동결융해 저항성 등에서 방음벽 재료로서 적당한 성능을 발휘하였으며, 성능과 가격면에서 밸런스를 확보할 수 있는 배합을 도출할 수 있었다.

• 콘크리트학회논문집
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• 제15권4호
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• pp.566-573
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• 2003

본 연구에서는 기포콘크리트속에 연속공극율을 증가시켜 흡음률을 높이면서 강도를 증진시킨 강체형 흡음재의 제조를 목적으로 하였다. 실험결과, 기포첨가량을 증가시켜 연속공극률을 높일수록 흡음률이 증가하였으며, 재료두께 5cm인 경우 연속공극률 40%이상에서 평균흡음률 70%이상을 만족하였다. 또한 흡음재 두께의 증가는 중저음영역에서 흡음률 증가를 나타내었으며 평균흡음률 70%이상을 만족하는 기포콘크리트의 비중은 재료두께 5cm에서 0.4이하, 7cm에서 0.6이하로 나타났다. 그리고 평균흡음률 70%이상 만족하는 비중 0.4인 기포콘크리트의 압축강도는 시멘트분말도 3,000$\textrm{cm}^2$/g의 경우 1.37MPa이나, 시멘트분말도 8,000$\textrm{cm}^2$/g에서는 3.34MPa로 증가되었다. 따라서, 연속공극을 갖는 기포콘크리트의 압축강도는 시멘트분말도가 높을수록 증가하는 것으로 사료된다.