• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.5
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• pp.10-17
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• 1989

A new design method of lossy matching network for the microwave broadband ampilfier is presented by using seattering parameters instead od modeling of transistor. A lossy matching network is represented as the combination of 2 lossless networks between which lossy serial or parallel immittance is inserted without using specific topology, and so many useful matching cireuits can be realized. Also it is shown that linear transforming relation exists between gain and reflection coefficient of the amplifier, and the transforming equation is derived using scattering parameters. With this equation some constant gain circles can be drawn on reflection coefficient plane to get adequate reflection coefficient and gain. And since the relations between amplifier gain/reflection coefficient and the immittance of passive element are bilinear transformations. constant gain or reflection coefficients circles. Illustrative examples are presented to show the usefulness of proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.699-704
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• 2002

A method using beamforming algorithm has been developed to measure oblique incidence reflection coefficients of sound absorption materials. MUSIC(Multiple Signal Classification) method detects the angles of incidence and reflection. By separating the incident and reflected waves using beamforming method, the reflection coefficient is calculated. Spatial smoothing technique is also used to reduce the coherence between the incident and reflected waves. The test materials were modeled as a locally reacting surface. Numerical and experiment results are performed to verify the acuracy of proposed method.

• Journal of Korea Water Resources Association
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• v.35 no.1
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• pp.91-96
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• 2002

The present research describes the Bragg reflection of obliquely incident waves propagating over sinusoidally varying topographies. A numerical model based on the boundary element method is employed. Wave numbers providing Bragg reflection are calculated and compared to theoretical predictions. The reflection coefficients obtained from this model are also compared with those of the eigenfunction expansion method. A very good agreement is observed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.6
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• pp.438-444
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• 2003

A method using beamforming algorithm has been developed to measure oblique incidence reflection coefficients of sound absorption materials. MUSIC(multiple signal classification) method detects the angles of incidence and reflection. By separating the incident and reflected waves using beamforming method, the reflection coefficient is calculated. Spatial smoothing technique Is also used to reduce the coherence between the incident and reflected waves. Numerical and experiment results are performed to verify the accuracy of proposed method.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.205-208
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• 2002

Numerous studies have been performed to develop an analytical model that can predict the reflection of regular or irregular waves from a perforated-wall caisson breakwater. Though such irregular wave models as Suh et at. (2001) become available, regular wave models are still in extensive use because of their simplicity. In the present study, using the regular wave model of Fuggazza and Natale(1992), the reflection of irregular waves from a perforated-wall caisson breakwater was calculated in several different methods. First, the regular wave model was re-validated by the hydraulic model tests. Though the model somewhat over-predicted the reflection coefficients at larger values and under-predicted them at smaller values, overall agreement was pretty good between calculation and measurement. Then, the regular wave model was applied to calculate the irregular wave reflection in the experiments of Suh et at.(2001) and Bennett et al. (1992). In applying the regular wave model to irregular wave reflection, several different methods were used. The results showed that it is the most reasonable to use the regular wave model repeatedly for each frequency component of the irregular wave specuum with the root-mean-squared wave height for all the frequencies .

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.819-827
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• 2019

Bragg reflection of water waves by three kinds of surface-piercing fixed structures with rectangular, cosinoidal and triangular shapes is studied. Boundary element method is used to analyze the wave scattering by these structures based on the linear wave theory. Results of reflection and transmission coefficients are validated by comparing with those available in literature. These structures with proper configurations are proved to be effective in attenuating waves by using Bragg reflection, and the triangular structures are found to be the best choices among the structures with same width and same area. Systematic calculations are then carried out for the triangular structures by varying the number, the draft, the width, the gap and the combination of width and gap of the structures to analyze their influences on the characteristics of Bragg reflection. The results are of reference values for design of the structures to attenuate waves based on the Bragg reflection.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.553-558
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• 1995

The purpose of this paper is recovery of the profiles of the wave speed and density from the reflection coefficients of the continuously layered acoustic medium with depth dependent density and wave speed at various angles of incidence. A downward continuation or layer stripping algorithm, which recursively reconstructs the medium in increasing depth and then strips away the effects of the reconstructed portion of the medium, is the method with fewer computations than integral equation procedures. This paper implements an improved downward continuation algorithm that uses reflection data at several angles of incidence and performs a least-squares fitting at each depth. The result is a considerable improvement in performance over the usual downward continuation algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.222-227
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• 2005

The permittivity profile of PCB substrate in a wide bandwidth is obtained by applying the moment method to the reflection coefficients measured by an open-ended coaxial probe. In this paper, the relation between a reflection coefficients and the corresponding permittivity is expressed into an integral form and the reflection coefficient of PCB substrates with different thickness are calculated using the dispersive FDTD method. The simulation results assure the validity of our conversion procedure within $2.015\%$ error.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.271-278
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• 2013

The effective reflection coefficients of an obliquely incident wave on a multi-layered substrate coated with a uniaxially anisotropic alignment layer are derived. The effective reflection coefficients as well as explicit ellipsometric expressions are provided as a function of film constants of multiple layers together with magnitude of anisotropy, direction of optic axis, and thickness of the alignment layer. It is expected that by adapting these expressions to the conventional modelling technique, the ordinary refractive index, the extra-ordinary refractive index, the azimuth angle and the tilt angle of the optic axis, and the thickness of the aligned surface can be determined simultaneously together with the thickness and volume fraction of each layer beneath the alignment layer.

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.115-120
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• 2015

Explicit expressions are derived for the effective reflection coefficients of obliquely incident light on a multilayered substrate coated with two uniaxially anisotropic films. Based on these reflection coefficients, ellipsometric constants are obtained as function of the tilt and azimuthal angles of the optical axes of the uniaxial films. Explicit expressions are provided, which can be used to separate the effects of surface anisotropy for anisotropic film from that of its bulk anisotropy, so that these expressions may be utilized in characterizing the surface anisotropy of alignment layers.