• Journal of Ocean Engineering and Technology
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• v.7 no.1
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• pp.13-24
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• 1993

The dispersion in the oscillatory flow generated by gravitational waves above the spatially periodic repples is studied. The steady parts of equations describing the orbit of the passive particle in a two dimensional field are assumed to be simply trigonometric functions. From the view point of nonlinear dynamics, the motion of the particle is chaotic under externally time-periodic perturbations which come from the wave motion. Two cases considered here are; (i) shallow water, and (ii) deep water approximation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.8
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• pp.1363-1375
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• 2000

The electromagnetic scattering characteristics by a periodic strip grating on a grounded dielectric slab for TM polarization case are examined from the viewpoints of both the reflection grating and the leaky wave antenna problems. Numerical results far two kinds of Bragg blazing (resonance type and non-resonance type) phenomena are given and some discussions on the properties(complex propagation constants, scattering characteristics, and distributions of strip current density) are presented. The comparison of the Bragg blazing phenomena between TM and TE polarization cases are also given in detail.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.4
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• pp.270-274
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• 2019

In this paper, we analyze a planar electromagnetic absorber by using the mode matching technique(MMT). The proposed electromagnetic absorber has a periodic structure composed of a perfect conductor and ferrite, and the transmitted and reflected powers in response to the incident wave with parallel polarization are calculated according to the thickness of the plate. The proposed absorber shows a high absorption compared to the cases of periodic slits with vacuum or the ferrite plate itself. The solution to the reflected and transmitted powers by MMT is also verified with the results from a commercial simulator.

• Current Optics and Photonics
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• v.2 no.2
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• pp.140-146
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• 2018

In this paper, mesoscale optical surface structures are found to possess both geometric and wave optics features. The study reveals that geometric optic analysis cannot correctly predict the experimental results of light transmission or reflection by mesoscale optical structures, and that, for reliable analyses, a hybrid approach incorporating both geometric and wave optic theories should be employed. By analyzing the transmission patterns generated by the mesoscale periodic pyramid prism plates, we show that the wave optic feature is mainly ascribed to the edge diffraction effect and we estimate the relative contributions of the wave optic diffraction effect and the geometric refraction effect to the total scattering field distribution with respect to the relative dimension of the structures.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.2
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• pp.151-156
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• 2021

Leakage and Bragg condition of optical waveguide with asymmetric rectangular grating profile are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. The optical waveguide composed by asymmetric rectangular grating occur leaky-wave stop-bands at Bragg conditions, and anomalies based on Rayleigh-Wood condition near Bragg conditions. Furthermore, DFB properties of the guiding structure at Bragg conditions are analyzed by applying longitudinal equivalent transmission-line with characteristic impedance of periodic grating. The numerical results show that filtering characteristics that maximize the reflected power of DFB waveguide are activated near Bragg conditions, in which leaky-wave stop-bands occur.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.17-24
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• 2001

Two-dimensional binary-phase diffraction gratings which can be employed to fabricate two- and three-dimensional periodic structures are designed and analyzed using rigorous coupled-wave analysis. These gratings serve as phase-masks which generate several diffracted waves from a normally incident beam and thus can produce a periodic interference pattern in space via nearfield holography. The properties of the diffracted beams can be controlled by varying the polarization and wavelength of the incident beam, surface-profile, groove depth and duty cycle of the mask. For the two-dimensional structure, optimum results can be obtained when the diffraction efficiency of the zero-order beam is minimized while that of the first-order maximized. On the other hand, when the diffraction efficiency of the zero-order is appreciable or even greater than other orders, we can obtain a variety of three-dimensional interference patterns which may be used to fabricate photonic crystals of tetragonal-body-centered and hexagonal structures in a submicron scale. scale.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.247-256
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• 1999

The leaky wave emanated from the dielectric-coated parallel-plate waveguide with finite periodic thick slot in its upper plate is investigated theoretically for H-polarization case. For this structure, fields in slot regions are expressed as a summation of the parallel-plate waveguide TM modes, and in other regions are expressed in the spectral domain by use of the inverse Fourier transform. Boundary conditions at the interfaces are enforced, and the simultaneous linear equations are derived. The influences of the slot width, slot thickness, thickness of a dielectric coating, and finite slot number on the radiation characteristics (phase constant, leakage constant, radiation pattern) are examined. The results of the finite periodic slot are compared with those of the infinite extent structure and good agreement has been found.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.107-111
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• 2010

The damage of tire by damage material classification method is researched as used ultrasonic wave signal to occur at a tire during vehicle driving. Auto-correlation function after having passed through an envelope detecting preprocess is used for detecting periodicity because of occurring periodic ultrasonic waves signal with tire revolution. One revolution cycle time of a damaged tire and period that calculated auto-correlation function appeared equally in experiment. The result that can classification whether or not there was a tire damage is established.

• Steel and Composite Structures
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• v.22 no.2
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• pp.277-299
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• 2016

In this paper, free vibration, forced vibration, resonance and stress wave propagation behavior in nanocomposite plates reinforced by wavy carbon nanotube (CNT) are studied by a mesh-free method based on first order shear deformation theory (FSDT). The plates are resting on Winkler-Pasternak elastic foundation and subjected to periodic or impact loading. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In the mesh-free analysis, moving least squares (MLS) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method is used for imposition of essential boundary conditions. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of elastic foundation coefficients, plate thickness and time depended loading are examined on the vibrational and stresses wave propagation responses of the nanocomposite plates reinforced by wavy CNT.

• Journal of the Chungcheong Mathematical Society
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• v.20 no.3
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• pp.261-267
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• 2007

We show the existence of the positive solution for the system of the following nonlinear wave equations with Dirichlet boundary conditions $$u_{tt}-u_{xx}+av^+=s{\phi}_{00}+f$$, $$v_{tt}-v_{xx}+bu^+=t{\phi}_{00}+g$$, $$u({\pm}\frac{\pi}{2},t)=v({\pm}\frac{\pi}{2},t)=0$$, where $u_+=max\{u,0\}$, s, $t{\in}R$, ${\phi}_{00}$ is the eigenfunction corresponding to the positive eigenvalue ${\lambda}_{00}=1$ of the eigenvalue problem $u_{tt}-u_{xx}={\lambda}_{mn}u$ with $u({\pm}\frac{\pi}{2},t)=0$, $u(x,t+{\pi})=u(x,t)=u(-x,t)=u(x,-t)$ and f, g are ${\pi}$-periodic, even in x and t and bounded functions in $[-\frac{\pi}{2},\frac{\pi}{2}]{\times}[-\frac{\pi}{2},\frac{\pi}{2}]$ with $\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}f{\phi}_{00}=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}g{\phi}_{00}=0$.