• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.1
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• pp.261-267
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• 2015

The eigenvalue problems involving the diffraction of waves by multi-layered grating configurations can be explained by rigorous modal expansion terms. Such a modal solution can be represented by equivalent transmission-line networks, which are generalized forms of simple conventional circuits. This approach brings considerable physical insight into the grating diffraction process of the fields everywhere. In particular, the transmission-line representation can serve as a template for computational algorithms that systematically evaluate dispersion properties, radiation effects and other optical characteristics that are not readily obtained by other methods. To illustrate the validity of the present rigorous approach, the previous research works are numerically confirmed and the results agree well each other.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.151-156
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• 2020

To analyze the diffraction properties of optical signals and the significant impacts of tapered sidewall profile at periodic trapezoidal 2D diffraction gratings, Toeplitz dielectric tensor is first defined and formulated by 2D spatial Fourier expansions associated with trapezoidal profile. The characteristic modes in each layer is then based on eigenvalue problem, and the complete solution is found rigorously in terms of modal transmission-line theory (MTLT) to address the pertinent boundary-value problems. Based on those one, the numerical analysis is performed on how the tapered side profile of grating structures with trapezoidal refractive index distribution affects the design of a sub-wavelength grating reflector. The numerical results reveal that this tapered sidewall profile plays a critical role in determining the reflection bandwidth, the average reflectance, and the band edge.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.275-286
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• 2021

In this study, the analytical solution for diffraction near a vertical detached breakwater was suggested by superposing the solutions of diffraction near a semi-infinite breakwater suggested previously using linear wave theory. The solutions of wave forces acting on front, lee and composed wave forces on both side were also derived. Relative wave amplitude changed periodically in space owing to the interactions between diffracting waves and standing waves on front side and the interactions between diffracting waves from both tips of a detached breakwater on lee side. The wave forces on a vertical detached breakwater were investigated with monochromatic, uni-directional random and multi-directional random waves. The maximum composed wave force considering the forces on front and lee side reached maximum 1.6 times of wave forces which doesn't consider diffraction. This value is larger than the maximum composed wave force of semi-infinite breakwater considering diffraction, 1.34 times, which was suggested by Jung et al. (2021). The maximum composed wave forces were calculated in the order of monochromatic, uni-directional random and multi-directional random waves in terms of intensity. It was also found that the maximum wave force of obliquely incident waves was sometimes larger than that of normally incident waves. It can be known that the considerations of diffraction, the composed wave force on both front and lee side and incident wave angle are important from this study.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.263-266
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• 2000

An elliptical ogive head for a generic missile is proposed to reduce its detectable probability from a ground defense radar. Numerical RCS results of a generic missile with an elliptical ogive head are evaluated using the GTD/UTD (Geometrical Theory of Diffraction/Uniform GTD). The results are compared with those of a cylindrical ogive head. In the sense of aerodynamics, the Performance evaluation of an elliptical ogive head for a generic missile should be followed.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.411-414
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• 1999

Insertion loss of partially Inclined noise harrier Is studied by using multiple diffraction theory. The diffractions occurred at the top as well as partially folded point are included based on Kouyoumjian and Pathak's method (Procd. IEEE, Vol. 62, 1974). Scaled-down model of noise barrier is studied in anechoic rooom. It is shown that the theoretical results generally represents the average values of experimental results, while there are many oscillations in experimental results.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1988.10a
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• pp.114-117
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• 1988

In mobile radio communication system involving geostationary satellites the field intensity of electromagnetic wave varies with frequency shape and location of an obstacle between a tramamitter and a receiver. In this paper a ring type obstacle between the propagation paths is presented. On the basis of Fresnel diffraction theory, the field intensity varying with ring-type obstacle’s radius is obtained by computer simulation.]

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.10
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• pp.48-53
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• 1994

The problem of a plane wave impinging upon a semi-infinite paralle-plate waveguide is investigated. The interior fields can be analyzed by converting the initial field into vaveguide modes. Kirchhoff approximation is usually made at the waveguide aperture in the literature. In this paper, a modified approximation is made using the Uniform Gemetrical Theory of Diffraction(UTD). Numerical results show excellent agreement between UTD-supplemented mode-matching solution and UTD solution.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.50-51
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• 2000

가속된 전자빔을 금속회절격자의 위로 통과시킬 때 결맞은 복사광(coherent radiation)이 발생하는데 이를 Smith- Purcell 효과라고 한다. 이때 발생하는 전자기파의 파장은 회절격자의 주기, 전자빔의 속도 및 복사광의 방출각도에 관계된다$^{(1)}$ . 그리고 방출된 복사광의 출력세기는 전자빔의 군집을 고려하지 않는 경우, 회절이론(diffraction theory)에 의해 얻을 수 있는데, 그 세기는 입사시킨 전자빔의 전류세기에 선형적으로 비례한다$^{(2)}$ . (중략)

• Transactions of the Society of Information Storage Systems
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• v.5 no.2
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• pp.64-69
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• 2009

In this paper, we investigate field distribution and interference pattern in the exit pupil and in the focal region. Also, we compare with metal and dielectric substrate for near-field recording. To obtain field distribution, we use modified vector diffraction theory and Zernike Polynomials. Finally, we design and optimize refractive index and thickness of disk for near-field surface recording and cover-layer incident recording.

• Journal of the Korean Society of Marine Environment & Safety
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• v.1 no.2
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• pp.61-67
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• 1995

This study examines experimentally and theoretically, the wave deformation by two large cylindrical structure in relation to the case of one structure. The wave height around the structures varies, according to the changes of the incident wave angles, the number of the structure, and the distances between the two structures. The wave deformation around the large cylindrical structures is shown to be well predicted theoretically by the diffraction theory based on the singular point distribution method using a vertical line wave source Green's function.