• The Journal of the Acoustical Society of Korea
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• v.13 no.2E
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• pp.83-91
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• 1994

Three components contribute to the acoustic field propagating in a wedge or over a ridge : a direct path arrival, an image component due to reflection from the boundaries and a component diffracted by the apex. All three contributions are included in a new, exact solution of the Helmholtz equation for the three-dimensional time harmonic field from a point source in a wedge(or over a ridge) formed by two intersecting, pressure-release plane boundaries. The solution is obtained by applying three integral transforms, and consists of and infinite sum of uncoupled normal nodes. The mode coefficients are given by a finite integral involving a Gegenbauer polynomial in the integrand, which may be computed relatively efficiently. Results of the theory for propagation over a 90 degree ridge is discussed.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.265-268
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• 1999

In this paper, a wideband MMIC distributed amplifier was designed using the fabricated PHEMT with the unit gate width of 80 ${\mu}{\textrm}{m}$ and 4 gate fingers at our Lab. S$_{21}$ gains are 7.1 ~ 10.0 ㏈. Input and output reflection coefficients obtained from the distributed amplifier in the frequency range of DC~25 ㎓ are lower then -8 ㏈. A chip size of the designed wideband MMIC distributed amplifier is 1.9 mm $\times$ 1.1 mm.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.199-203
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• 2016

An enzyme-free optical method is proposed for estimating high concentrations of glucose in a glucose-lactose mixture, based on a predictive equation that takes advantage of the reflective optical power observed at two discrete wavelengths. Compared to the conventional absorption spectroscopy method based on Beer's Law, which is mainly valid for concentrations below hundreds of mg/dL, the proposed scheme, which relies on reflection signals, can be applied to measure higher glucose concentrations, of even several g/dL in a glucose-lactose mixture. Two probe wavelengths of 1160 and 1300 nm were selected to provide a linear relationship between the reflective power and pure glucose/lactose concentration, where the relevant linear coefficients were derived to complete the predictive equation. Glucose concentrations from 2 to 7 g/dL in a glucose-lactose mixture were efficiently estimated, using the established predictive equation based on monitored reflective powers. The standard error of prediction was 1.17 g/dL.

• Journal of Power System Engineering
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• v.17 no.2
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• pp.56-62
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• 2013

A technique is presented that uses a circular waveguide for the measurement of the bulk shear (S-wave) velocities of unconsolidated, saturated media, with particular application to near surface soils. The technique requires the measurement of the attenuation characteristics of the fundamental torsional mode that propagate along an embedded pipe, from which the acoustic properties of the surrounding medium are inferred. From the dispersion curve analysis, the feasibility of using fundamental torsional mode which is non-dispersive and have constant attenuation over all frequency range is discussed. The principles behind the technique are discussed and the results of an experimental laboratory validation are presented. The experimental data are best fitted for the different depths of wetted sand and the shear velocities are evaluated as a function of depths. Also the characteristics of the reflected signal from the defects are examined and the reflection coefficients are calculated for identifying the relation between defect sizes and the magnitude of the reflected signal.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.314-318
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• 2000

For one-dimensional structures, a vibration response consists of direct and reflected waves from boundaries. Based on this concept of separable wave components, a modified travelling wave method (MTWM) is proposed in this paper: while all allowable waves are assumed and the boundary conditions are applied on by the conventional travealling wave method (TWM), in the proposed MTWM direct and reflected waves are assumed within the beam element, and the governing relations between direct and reflected waves are described in terms of the reflection or transmission coefficients. It is shown that the vibration response with considerable accuracy can be obtained compared to TWM for single and coupled beams. It is also shown that the band analysis to obtain quadratic response, or power flow response can be carried out by a slight change of the governing equations for one-dimensional structural systems. It is thought that the suggested MTWM can be used as a unified approach for predicting linear spectral response and/or quadratic band response involved in the one-dimensional structural vibration.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.799-804
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• 2018

In this paper, a method for measuring the dielectric constant of a planar dielectric substrate using the free space material constant measurement method in a general measurement environment is proposed. Two horn antennas and a network analyzer were used for S-parameter measurement and the transmission and reflection coefficients of a planar dielectric substrate were calculated from the measurement results. To obtain a reliable dielectric constant in a low-precision-measurement environment, only the magnitude of the transmission coefficient, which has a small error due to the measurement environment, is used for dielectric constant estimation. Finally, the dielectric constant is determined by comparing the measured results at different frequencies.

• International Journal of Contents
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• v.2 no.1
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• pp.29-33
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• 2006

The common-source low noise amplifier(LNA) with inductive degeneration using a genetic algorithm is designed and tested for a down converter in an industrial, scientific and medical (ISM) band application and a wireless broadband internet service (WiBro). The genetic algorithm optimizes the reflection coefficients to be well matched the input and output ports between multistage transistor amplifiers, and it generates low voltage standing wave ratio as well as gain flatness of the amplifier. The stability and the gain flatness of the LNA have been improved by combining the matching circuits and the series feedback microstrip lines with inductive degeneration at common-source port. In the frequency range of ISM band and WiBro application operating at $2.3GHz{\sim}2.5GHz$, the measured power gain and maximum voltage standing wave ratio (VSWR) of the LNA are $41{\pm}0.5dB$ and 1.3, and the noise figure of the LNA is lower than 0.85dB. The above results are agreed well with the theoretical values of the amplifiers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.3
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• pp.219-226
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• 1995

The wave interaction with flexible membrane such as PVC and PU fabrics is studied to prove its applicability to portable breakwaters. To analyze the wave deformation due to the flexible membrane. eigen-function expansion method is employed. The fluid domain is seperated into two regions. The velocity potential in each regions and the deformation of membrane are coupled by the body boundary conditions. Herein the deformation of membrane is obtained by solving the membrane equation. As a numerical example, transmission and reflection coefficients according to the change of several design parameters such as tensile force. mooring line stiffness and membrane height are investigated. It is found that the efficiency of flexible membrane breakwater is significantly affected by these design parameters. The angle of incident wave is an important role to the performance of breakwater. Finally we conclude that flexible membrane can be used to engineering material for the future breakwaters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1B
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• pp.120-127
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• 2000

In this paper, we propose multispectral image compression using classified interband prediction and vector quantization in wavelet domain. This method classifies each region considering reflection characteristics of each band in image data. In wavelet domain, we perform the classified intraband VQ to remove intraband redundancy for a reference band image that has the lowest spatial variance and the best correlation with other band. And in wavelet domain, we perform the classifled interband prediction to remove interband redundancy for the remaining bands. Then error wavelet coefficients between original image and predicted image are intraband vector quantized to reduce prediction error. Experiments on remotely sensed satellite image show that coding efficiency of theproposed method is better than that of the conventional method.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.102-109
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• 2000

This paper describes two different theories used to model the scattering of ultrasound by a volumetric flaw and a crack-like flaw. The elastodynamic Kirchhoff approximation (EKA) and the geometrical theory of diffraction (GTD) are applied respectively to a cylindrical cavity and a semi-infinite crack. These methods are known as high frequency approximations. The 2-D elastodynamic scattering problems of a plane wave incident on these model defects are considered and the scattered fields are expressed in terms of the reflection and diffraction coefficients. The ratio of the scattered far field amplitude to the incident wave amplitude is computed as a function of the angular location and compared with the boundary element solutions.