• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.417-426
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• 2006

A Digital X-ray imaging system using Compton backscattering has been developed to obtain a cross-sectional profile and mass loss of corroded lap-splices of aging aircraft from density variation. A slit-type camera was designed to focus on a small scattering volume inside the material, from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the lap-joint is scanned by moving the scattering volume through the thickness direction of the specimen. The mass loss of each layer has been estimated from a Compton backscatter A-scan to obtain the thickness of each layer including the aluminum sheet, the corrosion layer and the sealant. Quantitative information such as location and width of planar corrosion in the lap splices of fuselages is obtained by deconvolution using a nonlinear least-square error minimization method(BFGS method): A simple reconstruction model is also introduced to overcome distortion of the Compton backscatter data due to attenuation effects attributed to beam hardening and quantum noise.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.16-21
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• 2005

Photonic crystals, periodic structure with a high refractive index contrast modulation, have recently become very interesting platform for the manipulation of light. The existence of a photonic bandgap, a frequency range in which the propagation of light is prevented in all directions, makes photonic crystal very useful in application where the spatial localization of light is required, for example waveguide, beam splitter, and cavity. However, the fabrication of 3 dimensional photonic crystals is still difficult process. A concept that has recently attracted a lot of attention is a planar photonic crystal based on a dielectric membrane, suspended in the air and perforated with two dimensional lattice of hole. The fabrication of Si master with pillar structure using hot embossing process is investigated for two dimensional, low-index-contrast photonic crystal waveguide. From our research we show that the multiple stamp copy process proved to be feasible and useful.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.161-166
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• 2007

In this paper, two 4$\times$4 rectangular patch array antennas operating at 20 GHz are implemented for the satellite communication. The sixteen patch antennas and microstrip feeding line are printed on a single-layered substrate. The design goal is to achieve high directivity and gain by optimizing design parameters through permutations in element spacing. The spacing between the array elements is chosen to be 0.736$\lambda$. Numerical simulation results indicate that the HPBW(Half-Power Beam Width) of the 4$\times$4 patch array antenna is 18.78 degrees in the E-plane and 18.48 degrees in the H-plane with a gain of 17.18 dBi. Numerical simulations of a 4$\times$4 recessed patch array antenna yield a HPBW of 18.71 degrees in the E-plane and 17.82 degrees in the H-plane with a gain of 19.43 dBi.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.91-110
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• 2013

This paper proposes a novel iterative procedure for the design of planar reinforced concrete structures in which the reinforcement is designed for stresses calculated in a nonlinear finite element analysis. The procedure is intended as an alternative to strut and tie modeling for the design of complex structures like deep beams with openings. Practical reinforcement arrangements are achieved by grouping the reinforcement into user defined horizontal and vertical bands. Two alternative strategies are proposed for designing the reinforcement which are designated A and B. Design constraints are specified in terms of permissible stresses and strains in the reinforcement and strains in the concrete. A case study of a deep beam with an opening is presented to illustrate the method. Comparisons are made between design strategies A and B of which B is shown to be most efficient. The resulting reinforcement weights are also shown to compare favorably with those previously reported in the literature.

• Structural Engineering and Mechanics
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• v.68 no.2
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• pp.183-191
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• 2018

In this paper, harmonic responses of infilled multi-storey frames are obtained by using a single variable shear deformation theory (SVSDT) and dynamic stiffness formulations. Two different planar frame models are used which are fully infilled and soft storey. The infill walls are modeled by using equivalent diagonal strut approach. Firstly, free vibration analyses of bare frame and infilled frames are performed. The calculated natural frequencies are tabulated with finite element solution results. Then, harmonic response curves (HRCs) of frame models are plotted for different infill wall thickness values. All of the results are presented comparatively with Timoshenko beam theory results to reveal the effectiveness of SVSDT which considers the parabolic shear stress distribution along the frame member cross-sections.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1347-1350
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• 2006

We developed a new configuration of polarized light out-coupling lightguide plate (LGP) in the LCD backlight. By collimating the light into the LGP, one linear polarization component experienced total internal reflection at the planar interface of LGP and anisotropic layer, whereas the orthogonal polarization was out-coupled in the normal direction through a birefringent layer and subsequent isotropic microstructures.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.7
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• pp.865-874
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• 2016

This research is concerned with the experimental investigation on the vibrations of a flexible two-link system for verifying the theoretical result from simplified equations of motion for the system along with the kinematical synthesis are proposed to simulate the elastic vibrations of a previous study. The structure consists of flexible two-links; The link 2 is attached to the end of the link 1. The link 1 is made of composite fiber reinforced polymer and the link 2 is an aluminum beam. In order to verify the theoretical result, a flexible two-link system operated by the AC and RC servo motors was constructed. Experimental results show that the dynamic modeling approach and the kinematical synthesis proposed in this paper are effective.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.335-345
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• 2017

Free vibration analysis for continuous bridge under any number of vehicles is conducted in this paper. Calculation strategy for natural frequency and mode shape is proposed based on Euler-Bernoulli beam theory and numerical assembly method. Firstly, a half-car planar model is adopted; equations of motion and displacement functions for bridge and vehicle are established, respectively. Secondly, the undermined coefficient matrices for wheels, vehicles, intermediate support, left-end support and right-end support are derived. Then, the numerical assembly technique for conventional finite element method is adopted to construct the overall matrix of coefficients for whole system. Finally, natural frequencies and corresponding mode shapes are determined based on iterative method and overall matrix solution. Numerical simulation is presented to verify the effectiveness of the proposed method. The results reveal that the solutions of present method are exact ones. Natural frequencies and associate modal shapes of continuous bridge under different conditions of vehicles are investigated. The influences of vehicle parameters on natural frequencies are also demonstrated.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.99-102
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• 1999

평면 배열에서 원하는 빔패턴을 얻고자 할 때 각각의 소자들의 자체 방사특성 에 의해 다른 소자가 영향을 받게된다. 보통 이러한 영향은 빔패턴의 변화를 가져올 뿐만 아니라 소자의 성능을 저하시키게 된다. 이러한 간섭을 줄이기 위해서 배열 형태를 바꾸는 등의 구조적인 개선은 많이 시도되어 왔다 그러나 이러한 개선을 통하여 영향을 줄일 수는 있으나 보다 더 정확하게 원하는 사양의 빔을 설계하기 위해서는 최적화 기법을 통하여 이러한 영향을 보상해 주어 야 한다. 본 논문에서는 빔을 설계할 때 상호 간섭 영향을 포함시킨 빔설계 알고리듬을 소개한다. 이 알고리듬은 선형 최소자승법의 해를 기반으로 최적화를 수행하고 상호 간섭의 영향은 coupling coefficients matrix를 도입하였다. 이러한 방법으로 빔을 설계하게 되면 소자의 위치 등을 변화시키지 않으면서 원하는 사양의 빔을 설계 할 수 있게 된다.

• The Journal of the Acoustical Society of Korea
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• v.28 no.2E
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• pp.51-59
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• 2009

Mutual radiation impedance becomes more important in the design and analysis of acoustic transducers for higher power, better beam pattern, and wider bandwidth at low frequency sonar systems. This review paper focused on literature survey about the researches of mutual radiation impedance in the acoustic transducer arrays over 60 years. The papers of mutual radiation impedance were summarized in terms of transducer array structures on various baffle geometries such as planar, cylindrical, spherical, conformal, spheroidal, and elliptic cylindrical arrays. Then the computation schemes of solving conventional quadruple integral in the definition of mutual radiation impedance were surveyed including spatial convolution method, which reduces the quadruple integral to a double integral for efficient computation.