• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1140-1148
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• 2006

In this paper, transmission loss of smart panel was investigated using piezoelectric shunt damping. Admittance of piezoelectric system was introduced to represent electro-mechanical coupling of smart panel and to predict the performance of shunt damping. Finite element method was used to obtain numerical admittance. In order to illuminate the effect of noise reduction in the shunt system, transmission loss of the smart panel was investigated. Two models were considered to show the relation between admittance and transmission loss of smart panel. It was observed that admittance of piezoelectric system could be used as a design index of smart panel.

• Journal of the Korean Society for Railway
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• v.11 no.5
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• pp.465-470
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• 2008

Sound transmission characteristics are investigated on the honeycomb panels used for railway vehicles. Equivalent orthotropic plate model and equivalent mass law are applied to predict the sound transmission loss (STL) of the honeycomb panels. The predicted values of the STL are compared with the measured values. The reliability and the limitation of the prediction models are investigated. Coincidence effect and local resonance effect on STL are considered. The result of the study shows that the equivalent orthotropic plate model can be used as a good prediction model, if the local resonance frequency is properly applied. finally, ways to improve the severe STL drop by local resonance are proposed and the effect on the sound insulation performance is analysed.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.115-116
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• 2006

UWB 시스템은 실내 LBS 에 가장 유망한 기술로 각광받고 있다. 그러나 실내건물을 이루는 손실성 매질로 인해서 신호에 지연이 발생, 거리오차가 발생하게 된다. 본 문제를 해결하기 위해서 공기중의 채널과 매질의 채널정보를 통해서, 신호의 지연을 추정하려고 하였다. 신호의 스팩트럼의 주파수에 관한 손실기울기는 투과한 매질의 두께에 비례하여, 깊어진다는 것을 사용하여, 매질 투과로 인한 신호의 지연시간을 추정하는 기술과 손실기울기를 측정하기 위한 RAKE 수신기를 소개한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.1
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• pp.25-32
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• 2008

This paper presents the reflection and transmission measurements conducted at the 60GHz suitable to provide a high speed wide band service. Mean received power and standard deviation are calculated and used to compare the characteristics of radio wave propagation to the various obstacles between transmitting and receiving antennas at the frequency. The results show that the transmitted signal strength by the steel door and copper plate are about 40dB lower than in free space, those by the rubber plate, glass and styroform are about 3dB lower than in free space. Also, the re(looted signal strengths at the 60 degree grazing angle show that in case by the partition is about 23dB lower, by the surface of a wall is about 6dB lower than by the copper plate. The presented results can be used for the design of 60 GHz picocell communication network that the reflected and transmitted waves affect to the service area.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.302-311
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• 2022

Sound barrier walls are one of the most effective alternatives for reducing environmental noise on roads and railways in the city center. The insertion loss of the sound barrier against road traffic noise is the sum of the sound transmission loss, sound absorption loss, and sound energy reduction due to the diffraction attenuation of the sound barrier. The sound transmission loss of the sound barrier is one of the important factors that determine the insertion loss of the sound barrier and is a basic indicator that determines the performance of the sound barrier. Nevertheless, there is not a separate standard in Korea for measuring the acoustic transmission loss of sound barrier panels. There are only a few conditions in KS F 4770 series that stipulates on the general material of sound barrier panels. This thesis examines the necessity of the acoustic transmission loss measurement and evaluation standards of sound barrier walls, and seeks a measurement method in a free sound field (anechoic chamber) sound receiving room considering the characteristics of sound barrier walls installed in external spaces, unlike indoor building materials. In addition, a single number evaluation method using a reference spectrum was proposed so that the sound insulation effect according to various installation places such as roadside or railroad side can be easily displayed.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.375-388
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• 2022

This paper deals with the process of obtaining sound transmission loss of a cylindrical silencer lined with multi-layered poroelastic sound absorbing materials. The Biot model and the Johnson-Champoux-Allard-Lafarge (JCAL) model were used to deal with waves propagating in multi-layered poroelastic materials. The boundary conditions required for analysis of the silencer were obtained and the numerical process of finding modes was explained. A numerical experiment was conducted on the 2-layered silencer using the modes and the transmission loss converged with the first 12 modes. Finally, the mode matching method proposed in this research was validated by being compared with the results calculated from Finite Element Method (FEM) about different kinds of sound absorbing materials.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.92-99
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• 1998

The sound insulation capacity of honeycomb sandwich plates which have relatively higher strength ratios to weight is poorer than those of uniform and another sandwich plates. Therefore, improvement of the sound insulation capacity of the honeycomb sandwich plate which has a meritof lightness is required to use it in automobile and rapid rail road industries. In this study, to improving the sound insulation capacity of the honeycomb sandwich plate, the sound transmission loss of the structure is experimentally investigated by adding a viscoelastic damping layer, The effective add position and thickness of the layer were investigated from the viewpoints of both sound transmission loss and improved sound transmission loss over the frequency range from 800Hz to 10kHz.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.233-234
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• 2004

각종 재료의 음향투과손실을 간단히 비교 시험할 수 있는 관내법이 향후 국제규격으로 제정될 것에 대비하여 우선 KS 규격 제정을 목적으로 제반 특성평가를 수행하였다. 이를 위해 임피던스관을 제작하고, 관 벽을 따라 시편을 지나 마이크로폰 위치까지 전달되는 진동량, 무반사처리부의 흡음률 등 기본적인 특성을 살펴보았다. 최종적인 검증을 위해 몇 가지 시편에 대해 투과손실을 측정하고 이론적 해석에 의한 예측 값과 비교하였다.

• Korean Journal of Optics and Photonics
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• v.8 no.6
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• pp.456-460
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• 1997

Several methods of aligning ring type cavities have been investigated for long time. The measurement of cavity transmission spectrum control is somewhat effective due to aligning cavity with measuring cavity loss at the same time. In this research, four mirrors are aligned and attached by the measurement of pulse width of the transmitted light. The intracavity loss is optimized to about 0.98%, giving the calculated total reflection coefficient of about 99.02%.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.38-44
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• 2007

Using the mathematical model suggested by Bennet et al.(1992), the reflection and transmission coefficients by a circular pile breakwater has been investigated in the framework of potential theory. Flow separation due to sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of exact energy loss coefficient is critical to enhance the reliability of mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code. The energy loss coefficient can be obtained from the pressure difference between upstream and downstream. Energy loss coefficient is the function of porosity and the relation equation between them is suggested throughout the curve fitting processing. To validated the suggested relation, comparison between the analytical results and the experimental results is made for four different porosities with good agreement.