• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.625-628
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• 2005

Silencers are extensively used for reducing noise in an exhaust system of internal combustion Engine and fluid machineries. The prediction and measurement of the transmission loss as the acoustic performance of silencers are important in early design stage. In the measurement of transmission loss, the semi-anechoic terminations are general used for reducing unwanted effects by reflecting wave. However it is very hard to remove reflecting wave perfectly. So the research about the error made by reflecting wave is important. The analysis about errors made by reflections and modification techniques are proposed. For an application example, the diesel particulate filter (DPF) is chosen. The transmission loss of DPF is measured with and without considerations of reflecting wave.

• 전자공학회논문지A
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• 제32A권1호
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• pp.89-96
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• 1995

Lateral p-i-n photodiodes have been fabricated, electrically tested, and incorporated into microwave control circuits such as an optically excited microwave atttenuator and reflection type phase shifter. Circuit design procedures for the loaded-line phase shifter with the optically controlled p-i-n photodiode are presented. The equal loss loading mode presented for the first time for the phase shifter circuits with lossy load allows an equal insertion loss of the phase shifter in both of its phase states. It is found that the insertion loss of the equal loss loading mode phase shifter constructed with the fabricated p-i-n photodiode load are about 3dB for 11.25$^{\circ}$ bit and 1dB for 5.625$^{\circ}$ bit for the frequency range of 2GHz to 11GHz.

• 한국해양공학회지
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• 제19권2호
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• pp.90-93
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• 2005

An improved approximate formula is presented for Series 60 forms, modifying the approximate formula, developed by the Author in 1983. The weather formula is based on interpretations of detailed calculations of speed loss, due to wind(van Berlekom), motions(Maruo), and wave reflection resistance(Kwon). Comparison is made between the result of the approximate formula and the one of detailed calculation. The result of the formula is also compared with some published full-scale data for speed loss.

• 한국음향학회지
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• 제21권4호
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• pp.164-164
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.

• 한국위성정보통신학회논문지
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• 제9권3호
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• pp.104-108
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• 2014

한국형발사체의 표면에 장착되는 UHF-대역 안테나의 표면에 발생하는 결빙을 모델링하고, 이러한 결빙이 안테나의 공진주파수, 반사손실 및 방사패턴 등의 주요 특성에 미치는 영향을 분석하였다. 안테나 표면결빙을 모델링하기 위해 $-180^{\circ}C$의 얼음층에 대한 비유전율을 추출하였고 추출된 비유전율을 이용하여 안테나 표면결빙 모델을 제안하였다. 중심주파수가 UHF-대역인 안테나 표면에 1mm의 결빙이 되었을 경우의 표면결빙 모델을 적용하여 시뮬레이션 한 결과, 표면결빙에 의해 안테나의 공진주파수가 21MHz 하향 되었고, 방사패턴도 전 방향에 대해 전체적으로 10dB 이상의 성능저하가 발생되었다. 따라서 실제 안테나 표면에 결빙이 발생할 경우 안테나 성능에 심각한 영향을 미칠 것으로 판단된다.

• 한국전기전자재료학회논문지
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• 제27권7호
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• pp.462-467
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• 2014

In this paper, we studied the magnetic composite sheets for electromagnetic wave noise absorber of quasi-microwave band by using soft magnetic FeSiCr and Fe50Ni flakes with the thickness of about $1{\mu}m$ and polymer. The magnetic hysteresis curve including saturation magnetization and residual magnetization and the complex permeability characteristics of the composite sheets were investigated to clarify the mixing effect on electromagnetic wave absorption properties. The saturation magnetization was decreased about 10% while the residual magnetization was increased about 15% and the real parts of complex permeability at below 500 MHz were increased 0.6~4 while those values at above 500 MHz were decreased 0.4~2.5 according to the change of contents of FeSiCr and Fe50Ni powders. As a result, the reflection loss can be moved to the lower frequency from 2~3 GHz to 1~1.5 GHz as the contents of Fe50Ni flaky powder into FeSiCr flaky powder was increased up to 50%.

• 한국정보통신학회논문지
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• 제10권10호
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• pp.1744-1751
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• 2006

본 논문에서는 5.5GHz 대역 LNA와 $1{\times}2$마이크로 스트립 패치 안테나로 구성 된 무선 랜용 능동안테나를 설계 및 제작하였다. LNA는 NEC사의 NE3210S01을 사용하여 잡음 특성을 개선하였으며, 마이크로 스트립 패치 안테나는 전방향 특성을 갖도록 설계하였으며, 설계된 $1{\times}2$마이크로 스트립 패치 안테나는 약8.3dBi의 이득을 가지면서 입력 반사손실이 -32[dB], 전압정재파비가 1.132를 나타내었고, LNA는 이득이 15dB, 입출력 반사손실이 -20[dB]의 특성을 보였다.

• 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.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.271-271
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• 2013

The defect states of a Ar-sputtered SiO2 surface on Si (001) were investigated using Auger electron spectroscopy (AES) and reflection electron energy loss spectroscopy (REELS). The REELS spectra at the primary electron energy of 500 eV showedthat three peaks at 2.5, 5.1, and 7.2 eV were found within the band gap after sputtering. These peaks do not appear at the primary electron energies of 1,000 and 1,500 eV, which means that the defect states are located at the extreme surface of a SiO2/Si thin film. According to the calculations, two peaks at 7.2 and 5.1 eV are related to neutral oxygen vacancies. However, the third peak at 2.5 eV has never been previously reported and the theories proposed that this defect state may be due to Si-Si bonding. Our Auger data showed that a peak for Si-Si bonding at 89 eV appears after Ar ion sputtering on the surface of the sample, which is consistent with the theoretical models.

• 한국분말재료학회지
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• 제25권5호
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• pp.375-378
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• 2018

Conductive and dielectric SiC are fabricated using electroless plating of Ni-Fe films on SiC chopped fibers to obtain lightweight and high-strength microwave absorbers. The electroless plating of Ni-Fe films is achieved using a two-step process of surface sensitizing and metal plating. The complex permeability and permittivity are measured for the composite specimens with the metalized SiC chopped fibers dispersed in a silicone rubber matrix. The original non-coated SiC fibers exhibit considerable dielectric losses. The complex permeability spectrum does not change significantly with the Ni-Fe coating. Moreover, dielectric constant is sensitively increased with Ni-Fe coating, owing to the increase of the space charge polarization. The improvements in absorption capability (lower reflection loss and small matching thickness) are evident with Ni-Fe coating on SiC fibers. For the composite SiC fibers coated with Ni-Fe thin films, a -35 dB reflection loss is predicted at 7.6 GHz with a matching thickness of 4 mm.