• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.334-344
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• 2009

In the present paper, analytic solutions are derived for scattering of obliquely incident waves by a semi-infinite breakwater or a breakwater gap of partial reflection. In order to examine the appropriateness of the derived solutions, they are compared with the solutions derived by McIver in 1999 and Bowen and McIver in 2002 for a semi-infinite breakwater and a breakwater gap, respectively, in the case of perfect reflection. The derived analytic solutions are used to investigate the effect of reflection coefficient of the breakwater and wave incident angle upon the tranquility at harbor entrance. The tranquility is deteriorated by the reflected waves as the reflection coefficient increases and as the waves are incident more obliquely.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2008.09a
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• pp.160-163
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• 2008

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2008.09b
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• pp.160-163
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• 2008

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.186-196
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• 2000

In this paper, modified square loop frequency selective surface for dualband communication antenna systems is proposed, and the scattering characteristics is discussed. The analysis for the problem of scattering by periodic structures with a dielectric slab is formulated using the spectral-domain immittance approach and Floquet's theorem. The method of moments which uses rooftop subdomain basis function is employed to solve the equations. Numerical results include the comparison between the transmission characteristic of general square loop and that of modified square loop. Also, the transmission characteristics of modified square loop for arbitrary incident angle and polarization is presented. To verify analysis results, modified square loop frequency selective surface was fabricated and the calculated results were compared with the measured results. The measured results showed good agreement with the calculated results.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.7
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• pp.10-16
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• 2012

In this paper, we tried to realize a next generation MILES detection system which is robust to optical noise using a narrow band interference optical filter. Applying a narrow band interference optical filter which has the wavelength range of 895~915nm to the LASER wavelength of 900nm, we could obtain detection characteristics robust to strong optical noise which can be occurred in street battles. However, the MILES detection system has the blind range of detection in the incident angle range of $30^{\circ}{\sim}90^{\circ}$. To solve this problem we proposed a method of incident angle scatter using refractors. Applying a concave meniscus lens refractor which has diopter of 5.4 to the MILES detection system, we could eliminate the blind angle of detection.

• Proceedings of the KSRS Conference
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• 2007.03a
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• pp.138-141
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• 2007

본 논문에서는 제작이 간편하고, 저렴하여, 설치가 용이한 Trihedral comer reflector를 연결하여 전방향(omni-directional)에서 전파를 입사방향으로 반사하도록 전파반사기를 설계한다. Scale-down된 사각(Square) 형태와 원형(circular) 형태의 Retroreflector를 제작하고 RCS(radar cross section)의 각도별 패턴 특성을 측정하여 이론적, 수치 해석적 계산과 비교한 결과를 보인다. 측정된 RCS 절대 값과 패턴을 이론식 및 시뮬레이션 수치 해석 값과 비교하여 데이터의 적정성을 분석한다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.239-242
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• 1998

본 논문에서는 횡파를 이용한 STAM 시스템을 이용하여 다층구조물에 대한 토모그라픽 영상을 복원함으로써 토모그라픽 영상의 분해능을 개선시키는 방법에 관하여 연구하였다. 먼저, STAM 시스템의 수조에서 초음파가 시료로 입사될 때 입사각도에 따라 발생되는 종파와 횡파에 대한 모드변환에 관하여 고찰하였다. 실험을 위하여 시료로 각 층이 서로 다른 패턴을 갖는 2층의 알루미늄을 가공하여 다층구조물을 제작하였으며, 시료에 횡파를 여기시키기 위하여 초음파변환기의 입사각을 18$^{\circ}$로 사각 입사시킬 수 있는 웨지를 가공하여 수조를 제작하였다. 본 실험에서는 동작주파수가 10MHz인 STAM 시스템을 이용하여 4중 프로젝션에 대한 토모그라픽 데이터를 영상처리하여 토모그라픽 영상을 복원하였으며 이를 기존의 종파를 이용한 토모그라픽 영상과 비교분석한 결과, 콘트라스트와 축방향 분해능이 향상되고 토모그라픽 영상을 복원할 수 있었다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1060-1070
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• 2003

The frequency selective surface for use in Ka/Ku band parabolic antenna of domestic satellite communications is proposed. The frequency selective surface structure consists of the infinite periodic arrays of the triple square loop slot element with narrow width on the honeycomb structure of multi-layered dielectric. The frequency selective surface is fabricated and measured. The good agreement is obtained between theory and experiment. It is demonstrated that the frequency selective surface passes 14/12 GHz band wave while reflecting 30/20 GHz band wave as required.

• Korean Journal of Optics and Photonics
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• v.7 no.1
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• pp.17-23
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• 1996

At oblique angles of incidence, polarization properties of metal layers and dielectric layers are investgated and we designed the optical thin film systems reducing the variation of the polarization state, for target reflectances 0.5 and 0.6 at $45^{\circ}$ incidence in broad band wavelength regions $(\DELTA\lambda/\lambda= 10%)$ using two dielectric matching layers and one metal layer.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.51-56
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• 1997

In this paper, we studied the configuration and depth measurement method of the crack in the interior of solid with scanning laser acoustic microscope. Precision measurement method of crack depth is required in SLAM because that system reconstructs the shadow image to the transmission coefficient. We proposed this method that used geometrical structure to the shadow area of SLAM images obtained from oblique incidence and the mode conversion of ultrasound in specimen and then experimented it. For this experiment, we fabricated various specimens which had the vertical line-crack with different depth and made the wedge as 20$^{\circ}$ for oblique incidence. Experimental results showed that the shadow area of SLAM images were proportional to the depth of crack. Measured depth error to the crack was less than 6% compared with practical crack depth.