• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.591-595
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• 2000

Sound absorbing characteristics of poroelastic materials is known to be greatly affected by high intensity acoustic waves. However, this effect has not been considered yet. In this study, the extended semilinear model based on Biot's theory for the porous materials and the characteristics of nonlinear waves in poroelastic sound absorbing materials were introduced. The expressions for the finite-amplitude acoustic plane waves were presented. By combining each nonlinear wave with appropriate matching conditions, we could investigate the effects of finite-amplitude acoustic waves on absorption characteristics of poroelastic materials. In the most ideal case considered in this paper, the absorption coefficient was found to become larger than that of linear incident waves. It was shown that the absorption coefficient became greater especially as frequency goes higher and as distance from the source goes larger. These phenomena may be inferred to result from 'dissipation effects due to nonlinearity'. This finding may have important implications for high intensity noise control.

• 한국음향학회지
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• 제41권6호
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• pp.723-729
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• 2022

본 논문은 냉장고 기계실 내부 압축기의 저주파 대역에서 소음을 줄이기 위해 다공판을 사용하는 연구이다. 흡음 결과를 예측하기 위해 흡음재의 표면 임피던스를 측정하여, 측정된 임피던스 결과를 이용하여 Finite Element Method(FEM) 분석에 사용된 결과가 실험값과 거의 유사함을 확인하였다. 다공판의 구멍 직경과 배치를 조절하여 냉장고 기계실 내부의 목표 주파수 대역에서 동작할 수 있는 흡음구조를 설계하였다. 기계실에 다공판과 흡음재를 결합한 흡음구조를 적용하여 기존의 흡음재의 주파수 대역보다 낮아진 저주파대역 소음저감 효과를 확인하였다.

• 한국소음진동공학회논문집
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• 제21권1호
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• pp.81-88
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• 2011

The method is introduced for estimating the noise source contribution on the noise of PDP TV in a multiple-input system where the input sources may be coherent with each other. By the coherence function method, it is found that the biggest part of the noise source in the PDP TV noise is generated by the PCB boards which consume high power and produce high heat. This analysis is modeled as three-input/single-output system because the noise is generated by three main boards, X-board, Y-board, SMPS that are located close to each other. The coherence function method is proved to be useful tool for identifying of noise source. In this study, Transfer Path Analysis using MDSA is implemented to determine the quantitative noise contribution of each board for PDP TV with the rear case closed and with the rear case open. And the possibility of noise reduction is confirmed through the experimental method that isolates the most contributing board by adding sound-absorbing materials to it.

• 한국소음진동공학회논문집
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• 제20권8호
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• pp.742-752
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• 2010

In case of the working machine that using in the loud-noisy workplace, as it generates the loud-noise, it is influencing a physical, mental bad effect to those workers. Accordingly, though the noise countermeasure for the loud-noisy workplace is acutely requiring, until now, those methods that wearing the soundproof-protection tool, or restriction the working hours, and minimize the noise exposure volume, were mainly used. However, such noise countermeasures occur many problem points. On such point of view, using the acoustic simulation technique, let the workers to choose the workplace where suffering many damages due to the noise of working machine, and after grasp the physical property of working machine and indoor acoustic characteristic, this Study has attempted to grasp the reduction degree of noise level at before-improvement?after-improvement, through the sound-absorption measure. Passing through such preceding step, using auralizational technique based on the noise of working machine of before-improvement after-improvement, and by conduct psycho-acoustics evaluation, this study intended to investigate the change degree of subject reaction. As the result of evaluation, it is considering that the noise-reduction countermeasure method for the loud-noisy workplace could be much effective, through the sound-absorption measure.

• 한국분말재료학회지
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• 제20권2호
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• pp.125-128
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• 2013

Magnetic and dielectric properties of rubber composites are controlled by using two kinds of high-permeability metal particles with different electrical conductivity (Sendust, Permalloy), and their effect on microwave absorbance has been investigated, focusing on the quasi-microwave frequency band (0.8-2 GHz). Noise absorbing sheets are composite materials of magnetic flake particles of high aspect ratio dispersed in polymer matrix with various filler amount of 80-90 wt.%. The frequency dispersion and magnitude of complex permeability is almost the same for Sendust and Permalloy composite specimens. However, the complex permittivity of the Permalloy composite (${{\varepsilon}_r}^{\prime}{\simeq}250$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}50$) is much greater than that of Sendust composite (${{\varepsilon}_r}^{\prime}{\simeq}70$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}0$). Due to the large dielectric permittivity of Permalloy composite, the absorbing band is shifted to lower frequency region. However, the investigation of impedance matching reveals that the magnetic permeability is still small to satisfy the zero-reflected condition at the quasi-microwave frequency band, resulting in a small microwave absorbance lower than 10 dB.

• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.79-84
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• 2006

Acoustic characteristics of a sound absorbing material can be identified, if the characteristic impedance and propagation constants are known, which have generally been determined experimentally. One easy method determining these two essential parameters is to measure the one dimensional wave characteristics in the impedance tube. In th udy, the effects of backing conditions on the impedance tube measurement have been examined using several pairs of generally used end conditions. The results showed that the measured values are similar for most pairs of end conditions: however, it was observed that the measured characteristic impedance for different thickness did not agree well for some pairs. In this work, the multi termination method, using three or more known backing con ns, was suggested to reduce such random errors, which are mostly caused by the test procedure. Employing three terminations as a set, comprised of a rigid end, an end with porous material, and an end with a backing cavity, it was demonstrated that improved measured results could be obtained for an open cell PU foam varying widely with three different thicknesses.

• 한국소음진동공학회논문집
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• 제15권8호
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• pp.924-930
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• 2005

Sound absorptive materials have good performance in high frequency range, not at low frequencies. Therefore it has been great challenge to develop a sound absorbing structure that is good at low frequency. We propose to use a Helmholtz resonator array panel for this purpose. A Helmholtz resonator is one of noise control elements widely used in many practical applications. The resonator is a simple structure composed of a rigid-walled cavity with a neck, but it has very high performance at resonance frequency. This paper discusses the sound absorption of Helmholtz resonator array panels at normal and random incidence. First, various experimental results are introduced and studied. Secondly, we theoretically predict the absorptive characteristics of the resonator away panel. The theoretical approach is based on the Fourier analysis for a periodic absorber. We believe that this method can be used to design a panel for low frequency noise control.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.288-291
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• 2004

The Helmholtz resonator is one of noise control elements widely used in many practical applications. However the resonator array system, which is sometimes used to reflect or absorb low frequency noise, has not been well studied. We have investigated the difference in sound absorption of the Helmholtz resonator array panel caused by change in the resonator arrangement. Experiments and numerical calculations for various Helmholtz resonator array panels are carried out and the results are compared each other. The comparisons show that the acoustic coupling between closely located resonators affects the performance of the sound absorbing system. Particularly, the distance between resonators has a significant effect on the broadness of the sound absorption coefficient.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.131-136
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• 2004

Impact sounds, such as those created by footsteps, the dropping of an object or the moving of furniture, can be a source of great annoyance in residential buildings. The character and level of impact noise generated depends on the object striking the floor, on the basic structure of the floor, and on the floor covering. This study base on the evaluate of isolation performance of impact sound according to the impact noise reduction methods. Reduction methods consist of four ways. First way is increase thickness of bare floor and other ways are using the soft coverings on the floor and ceiling assembles. Last way is make floating floor with shock absorbing materials.

• 한국소음진동공학회논문집
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• 제14권9호
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• pp.811-818
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• 2004

Impact sounds, such as those created by footsteps, the dropping of an object or the moving of furniture, can be a source of great annoyance in residential buildings. The character and level of impact noise generated depends on the object striking the floor, on the basic structure of the floor, and on the floor covering. This study base on the evaluate of isolation performance of impact sound according to the impact noise reduction methods. Reduction methods consist of four ways. First way is increase thickness of bare floor and other ways are using the soft coverings on the floor and ceiling assembles. Last way is make floating floor with shock absorbing materials.