• 한국정보통신학회논문지
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• 제14권6호
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• pp.1331-1337
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• 2010

본 논문에서는 국방과학의 RF 스텔스 구현을 위해 필요한 RCS 감소용 RAM의 전파흡수능 측정기법에 대하여 연구하였다. 먼저 RAM의 전파흡수능에 대한 이론 정립 후 측정기법에 대하여 실제 레이더 시스템과 유사한 자유공간법과 실험실에서 용이한 전송선로법을 분석하여 실제 RAM 샘플을 제작하여 측정기법에 따라 측정후 비교 분석하였다. 비교 분석결과 전파흡수능은 자유공간법에서 다소 우수한 특성이 보였으나 전체적인 패턴이 유사한 것을 확인하였다. 따라서 RAM 개발시 초기단계부터 최종단계까지 단계별/주파수별 제시하는 측정기법을 차등 적용한다면 보다 효과적으로 RAM을 개발 할 수 있을 것이다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.527-530
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• 2010

본 논문에서는 RCS 감소용 RAM의 흡수능 측정기법에 대하여 연구하였다. 먼저 측정기법 중 자유공간법과 전송선로법을 분석하고 실제 RAM 샘플을 제작하여 측정기법에 따라 측정 후 비교 분석하였다. 비교 분석결과 흡수능은 자유공간법에서 다소 우수한 특성이 보였으나 전체적인 패턴이 유사한 것을 확인하였다. 따라서 RAM 개발시 초기단계부터 최종단계까지 단계별/주파수별 제시하는 측정기법을 차등 적용한다면 보다 효과적으로 RAM을 개발 할 수 있을 것이다.

• Journal of the Korean Wood Science and Technology
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• 제50권6호
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• pp.404-413
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• 2022

This study aims to investigate the sound absorption ability of Acanthopanax senticosus wastes as an eco-friendly sound-absorbing material. The sound absorption coefficient was examined with different heights of A. senticosus wastes filling (40, 60, 80, and 100 mm) in impedance tubes. The sound absorption peaks shifted to a lower frequency as the height of A. senticosus wastes inside the tubes increased. The sound absorption ability at filling heights of 80 and 100 mm was obtained as 0.3M and 0.5M grades, respectively, based on KS F 3503. The results suggest that A. senticosus wastes exhibit good sound absorption ability and can therefore be used as an efficient, eco-friendly sound-absorbing material.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.215-221
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• 2017

An electromagnetic (EM) wave absorber reduces the possibility of radar detection by minimizing the radar cross section (RCS) of structures. In this study, a radar absorbing structure (RAS) was applied to the leading edge of a blended wing body aircraft to reduce RCS in X-band (8.2~12.4GHz) radar. The RAS was composed of a periodic pattern resistive sheet with conductive lossy material and glass-fiber/epoxy composite as a spacer. The applied RAS is a multifunctional composite structure which has both electromagnetic (EM) wave absorbing ability and load-bearing ability. A two dimensional unit absorber was designed first in a flat-plate shape, and then the fabricated leading edge structure incorporating the above RAS was investigated, using simulated and free-space measured reflection loss data from the flat-plate absorber. The leading edge was implemented on the aircraft, and its RCS was measured with respect to various azimuth angles in both polarizations (VV and HH). The RCS reduction effect of the RAS was evaluated in comparison with a leading edge of carbon fabric reinforced plastics (CFRP). The designed leading edge structure was examined through static structural analysis for various aircraft load cases to check structural integrity in terms of margin of safety. The mechanical and structural characteristics of CFRP, RAS and CFRP with RAM structures were also discussed in terms of their weight.

• Journal of the Korean Wood Science and Technology
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• 제42권2호
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• pp.207-213
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• 2014

This study was carried out to investigate the feasibility and usefulness of a commercial synthetic adsorbent, Diaion HP 20, for the isolation of proanthocyanidins (PAs) from hot water extract (HWE) prepared from Pinus radiata bark. Most ultraviolet (UV) absorbing materials in HWE were adsorbed onto Diaion HP 20 and easily recovered by simple ethanol (EtOH) washing. More than 50% of the UV absorbing materials were adsorbed within 20 minutes, and the adsorption equilibrium was reached within 3 h. The recovered materials from Diaion HP 20 were mostly composed of PAs, but some monomeric flavonoids such as taxifolin and unidentified hydrophobic materials were also adsorbed. The impurities such as carbohydrates and inorganic materials contained in HWE were mostly removed by Diaion HP 20. The adsorption ability of the UV absorbing materials onto Diaion HP 20 was almost the same as the first cycle even after 14 times of repeating cycles of adsorption and desorption. The radical scavenging ability of the recovered materials from the adsorbent was slightly higher than that of the pure PAs prepared by Sephadex LH 20 from the same HWE.

• Journal of the Korean Wood Science and Technology
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• 제50권5호
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• pp.365-374
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• 2022

Today, commercialized Hinoki cypress cubes are used for fragrance, humidification, and pillows in Korea. In this study, the sound absorption ability of Hinoki cypress (Chamaecyparis obtusa) cubes was examined. The three groups of Hinoki cypress cubes were prepared depending on their dimension (L: 9 × 9 × 9, M: 7 × 7 × 7, S: 4 × 4 × 4 mm). Their sound absorption coefficient was examined after filling 6, 8, 10, and 12 cm height in impedance tubes, respectively. Overall, the sound absorption ability depending on dimension was superior in the M group compared to the L and S groups. Also, as the filling height increased, the sound absorption capacity increased. In sum, noise reduction coefficients (NRC) of all Hinoki cypress cubes were 0.41-0.59. Thus, this research found that Hinoki cypress cubes have a sound-absorbing function.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.105-108
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• 2002

Materials, matrices mixed with various kinds of conductive or magnetic powder, such as ferrite, have been used as the electromagnetic wave absorbing ones, so called RAM(radar absorbing material). The structure that does not only have electromagnetic waves absorbing property like RAM but also supports loads is called RAS(radar absorbing structure). One of the existing manufacturing process of RAS is to compound with conductive powders the glass fiber-reinforced composite with good permeability and the ability to support loads. The process, however, causes a number of problems, such as the degradation in the mechanical properties of the composite, especially, interlamina shear strength. In this study, mechanical properties of glass fabric/epoxy composite containing 7wt% carbon black powders were measured and compared with pure glass fabric/epoxy composites.

• Journal of the Korean Wood Science and Technology
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• 제50권3호
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• pp.179-185
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• 2022

This study investigated the prospect of using peanut shells as an alternative and green sound-absorbing material. The sound-absorption coefficients were determined after filling impedance tubes of 30, 60, and 90 mm in height with peanut shells. The sound-absorption ability increased as the filling height increased, showing noise reduction coefficient (NRCs) of 0.23, 0.43, and 0.54 for the 30-, 60-, and 90-mm heights, respectively. In addition, for sounds greater than 2,000 Hz, the average sound-absorption coefficient of peanut shells in the 60- and 90-mm heights was 0.9. In summary, peanut shells were found to have good sound-absorption properties comparable to or better than those of bamboo, sisal, jute, and wool, and this research suggests that peanut shells may be useful as an environmentally friendly sound-absorbing material.

• 지구물리와물리탐사
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• 제12권2호
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• pp.183-191
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• 2009

탄성파 수치 모형 계산에 있어서 널리 사용되는 엇갈린 격자 방법이 아니라 회전된 엇갈린 격자 방법을 사용하여 탄성파 수치 모사를 수행하였다. 표준 엇갈린 격자 방법에서는 특별한 자유 경계조건을 적용하여야 하는 단점이 있지만 회전된 격자 방법에서는 물성으로 진공 또는 공기층을 부여함으로써 자유 경계조건을 실현가능하다는 것을 확인할 수 있었다. 파동전파에 있어서 유한 경계 조건에서 발생하는 인공 반사파를 제거하기 위해 PML (Perfectly Matched Layer)의 파동식 분해라는 단점을 극복할 수 있고 좋은 성능을 보이는 CPML (Convolutional Perfectly Matched Layer)법을 회전된 엇갈린 격자법(RSG: Rotatged Staggered Grid)에 적용하였다. 회전된 격자 유한 차분법에서 CPML의 고주파수 흡수 특성과 에너지 흡수율 조사, Cerjan법의 감쇠를 비교한 결과 흡수경계조건으로 좋은 성능을 확인하였다. 유체와 고체의 모형에 대한 경계에 대하여서도 매우 효과적으로 경계면에서 발생하는 반사파를 제거할 수 있음을 알 수 있었다.

• 한국소음진동공학회논문집
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• 제15권2호
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• pp.161-168
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• 2005

The absorbing material is mostly used to changing the acoustic energy to the heat energy in the passive control, and that consists of the porous media. That controls an air borne noise while the stiffened plates, damping material and additional mass control a structure borne noise. The additional mass can decrease the sound by mass effect and shift of natural frequency, and damping material can decrease the sound by damping effect. The passive acoustic control using these kinds of control materials has an advantage that is possible to control the acoustic in the wide frequency band and the whole space at a price as compared with the active control using the various electronic circuit and actuator. But the space efficiency decreased and the control ability isn't up to the active control. So it is necessary to maximize the control ability in the specific frequency to raise the capacity of passive control minimizing the diminution of space efficiency such an active control. Therefore, the characteristics of control materials and the optimum layout of control materials that attached to the boundary of structure-acoustic coupled cavity were studied using sequential optimization on this study.