• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.644-654
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• 2019

In this study, the gas permeability, sound absorption coefficient, and sound transmission loss of the Paulownia tomentosa wood were estimated using capillary flow porometry, transfer function method, and transfer matrix method, respectively. The longitudinal specific permeability constant of the Paulownia tomentosa wood with a thickness of 20 mm was 0.254 for the control sample and 0.279, 0.314, and 0.452 after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$, respectively. The gas permeability was observed to be slightly increased by the heat treatment. The mean sound absorption coefficients of 20-mm thick Paulownia tomentosa log cross-section for the control sample and after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.101, 0.109, 0.096 and 0.106, respectively. Further, the noise reduction coefficients of 20-mm thick Paulownia tomentosa log cross-section of the control sample and after being subjected to heat treatment at temperatures of $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.060, 0.067, 0.062 and 0.071, respectively. The mean of sound transmission loss of the 20-mm thick Paulownia tomentosa log cross-section was approximately 36.93 dB. Furthermore, the gas permeability and sound absorption coefficient of the heat-treated Paulownia tomentosa discs slightly increased depending on the heat treatment temperature; however, the rate of increase was insignificant.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.287-292
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• 2004

This paper presents the effect of scratches on an optical connector interface surface on the insertion loss of optical connectors. We propose a model for calculating the insertion loss of optical connectors. The model is expressed in terms of geometrical parameters of scratches assuming that the transmission coefficient of a light wave on the scratch surfaces is linearly varied as a function of scratch depth. Geometrical parameters of scratches such as location, width, and depth of scratches are measured using 3D optical interferometry surface profiler. We obtain the equation of the transmission coefficient in terms of scratch depth comparing the experimental insertion loss data to the insertion loss data using the model presented in this paper. Using the model and the equation of the transmission coefficient presented in this paper, we present the results of the insertion loss of optical connectors for various geometrical parameters of scratches. Scratches which are located at longer than two times the core radius from the center of the core show negligible effect on the insertion loss of optical connectors.

• Journal of the Korean Solar Energy Society
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• v.35 no.1
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• pp.61-68
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• 2015

The advanced counties effort to the supplement of the zero energy buildings for the global building energy saving. In the middle of the development of passive technology, the government has to effort to the energy saving of buildings by enhanced performance of the window thermal insulation. By the method of enhanced performance of window thermal insulation, the use of vacuum double glazing saves the energy consumption in building. This glazing has low U-value(heat transmission coefficient) than normal double glazing. The vacuum glazing enhanced thermal insulation performance by vacuum space of between the glass and glass. For this vacuum glazing, pillar maintain the space between glass and glass. But this structure cause the raising the heat transmission coefficient in pillar approaching glass. This study confirmed the U-value by the test method of thermal resistance for windows and doors. Also this study confirmed the variation of heat transmission coefficient by the structure of vacuum glazing. And this study measured the surface temperature of the vacuum glazing about pillar approaching glass and vacuum space in cool chamber and hot box. That result, this study confirmed U-value of $0.422W/m^2{\cdot}K$ of vacuum glazing. Also this study confirmed U-value of $0.300{\sim}0.422W/m^2{\cdot}K$ by various the structure of vacuum glazing. And this study confirmed the heat flow in pillar approaching glass.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.192-199
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• 2015

There is a gap between the inner wall of a pulse tube and an underwater acoustic material when the measurement for transmission loss by the pulse tube is carried out. In this paper, the effect, which is caused by the gap, for the measurement of transmission loss is analyzed. Transmission coefficient is derived from the ratio of the pressures between front and rear of the gap. Then, transmission loss for specimen with a gap is obtained by combining the transmission coefficients of the gap and specimen. The results of experiment and simulation for a specimen of stainless steel with 10 mm thickness are compared in order to evaluate the simulation model. Finally, simulations with respect to the gap size and transmission loss of a specimen are performed to analyze and evaluate the effect of the gap in measurement of transmission loss.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.481-482
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• 2008

This investigation presents a method to design an optimal shape of a matching waveguide connecting two waveguides having different impedances. The design objective is to maximize power transmission through the waveguide system. When an incident wave impinges on an elastic waveguide system consisting of waveguides of different impedances, all of the incident wave power may not pass through due to the mechanical impedance. Therefore, the maximization of the transmitted power through a waveguide difficult to achieve without a systematic design method. In this work, the optimal shape design of a matching waveguide connecting two waveguides of different impedances is formulated as a shape optimization problem. If the material of the matching waveguide is given, its shape is the only parameter controlling the transmission power. Relatively simple one dimensional elastic wave transmission problems will be considered in this work, but the underlying methodology and the related physics can be clearly demonstrated. The influences of initial configurations as well as the target frequencies on the optimized shapes will be also investigated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.3
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• pp.304-310
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• 2014

This paper presents the analysis of the coupling coefficient(k), Q value of the resonator, and the optimum loaded resistance at Rx for the magnetically coupled wireless power transmission using two loops(resonators). In addition, the metamaterial, conductor, and the relay methods have been used in order to improve the limitation problem of transmission efficiency by using the figure of merit. We have achieved the increase of transmission efficiency about 11~60 % using the proposed methods by analyzing and comparing the results based on EM simulations.

• Composites Research
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• v.25 no.5
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• pp.154-158
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• 2012

The effect of structure on the sound absorption and sound transmission loss of composite sheet was investigated. A sheet of polypropylene was bonded by hot press with nonwoven fabric sheets of polyethylene terephthalate on the top side and the back side. Absorption coefficient of composite sheet using nonwoven fabric with surface density of $0.64kg/m^2$ was 0.1-0.2. It is 100-400% improvement compare to that of polypropylene sheet. The transmission loss of composite sheet was increased with surface density of polypropylene board and introduction of hemisphere hole on the surface of sheet. Two types of composite sheet were made using flat sheet and sine wave shaped sheet and the effect of sheet structure on the transmission loss was investigated.

• Journal of Satellite, Information and Communications
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• v.11 no.2
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• pp.69-73
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• 2016

In order to derive reliable propagation models for future millimeter-wave frequency indoor pico-cellular communications systems, accurate reflectivity data of building materials is necessary. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. This paper derives a transmission and reflection coefficient based on 13 GHz to 28 GHz measurement data. Transmission and reflection is measured by applying change in the reception angle of each building material, such as plasterboard. The transmission and reflection coefficient derived shows a correlation between frequency dependence and angle. As a result, as the reception angle is reduced, the reflected angle from the transmitter that could be received increases, showing that there is a correlation. In addition, the fundamental investigations carried out lay the foundation for radio channel-related research, which is essential for the development of future millimeter-wave communications systems.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1901-1903
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• 1999

To investigate invar alloy as a core material for increased capacity over-head transmission line which have high strength and low thermal expansion coefficient, hardness and thermal expansion coefficient of Fe-Ni-Co alloy have been studied. It is necessary that invar alloy have low thermal expansion coefficient and high strength for increased capacity over-head transmission line. In this paper. we tried to find out the effect of Ni and Co which has ferromagnetic properties and high saturation magnetization. It was found that Ni decrease thermal expansion coefficient and hardness, Co decrease thermal expansion coefficient but increase hardness in Fe-xNi-Co system. In Fe-(29-x)Ni-Co system, the material has no low thermal expansion properties substituting Co instead of Ni in concentration range of $1\sim7$%Co.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.898-906
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• 2002

In this paper, we investigated the improvement degree of transmission distance of the various initial frequency chirped optical pulse with 5 dBm initial power dependence on the various bit rate and fiber dispersion coefficient, when MSSI(Mid-Span Spectral Inversion) with the optimal pump power condition is adopted for the compensation method for optical pulse distortion. And we analyzed the influence of mutual relation of optical pulse frequency chirp and Kerr effect on the MSSI methods for the long-haul optical transmission through the computer simulation. We found that the compensation degree of distorted optical pulse varies as a consequence of the variation of combined phase modulation of self phase modulation(Kerr effect) and initial frequency chirp parameter dependence on the fiber dispersion coefficient. And we found that, if the transmission bit rate is increased k times, the dispersion coefficient value of dispersion shift fiber is decreased $2^k$ times so as to be almost the same performance of the transmission system with k times lower bit rate.