• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.996-1000
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• 2002

A porous tube, comprised of a resin-coated woven fabric has recently been used as an effective component for use in intake systems of internal combustion engines to reduce the intake roaring. For the prediction of the acoustic performance of an engine intake system with a porous woven hose, the acoustic wall impedance of the hose must be known. Because of its peculiar acoustical and structural characteristics, the accurate measurement of the wall impedance ofa porous woven hose is not easy. A new measurement technique is proposed herein, that is valid over the low to mid frequency ranges. The acoustics impedance is inversely estimated from an overdetermined set of measured pressure transmission coefficients for specimens of different lengths and the reflection coefficient of end termination. The method involves only one measurement, and, as a result, it is very simple. The measured TL for samples with arbitrary conditions, arbitrary porous frequency, arbitrary length, and arbitrary mean flow condition, are in reasonably good agreement with values predicted from curve-fitted impedance data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.6
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• pp.586-595
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• 2007

The analytic solution of wave scattering of monochromatic waves on a pile breakwater by an eigenfunction expansion method is extended to the case of directional irregular waves. The scattering wave spectrum and the force spectrum can be expressed from the reflection coefficient, transmission coefficient and the wave forces obtained from changing frequencies and incident angles in monochromatic waves. By numerical integration of 2-dimensional spectrum which is function of frequencies and incident angles, the representative values for the scattered waves and wave forces are obtained and the dependence of the transmission coefficients and wave forces on the directional distribution function, the principal wave direction, the submergence depth, and porosity is analyzed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.346-351
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• 2001

A new analysis method was proposed, where the even . odd-mode theory for a symmetrical coupled-line directional coupler was applied to a transformer-type directional coupler. In addition, the tap-offs were analyzed by the proposed theory, which are widely used in CATV (Cable Television), DBS (Direct Broad- casting Satellite), CS (Communication Satellite) systems. By comparing the calculation results to the measured ones using the even . odd-mode reflection coefficients only, the validity of the proposed analysis method was confirmed. Then, the tap-off has been broadened from 5 MHz over 4,000 MHz by adopting the proposed theory.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.79-80
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• 2016

In this paper, we considered a design method for a microstrip patch antenna fed through two radiating edges by two feeding microstrip lines. Two feedlines are made to have a phase difference of 180 degree with each other in order to reduce cross-polarization level radiated from the antenna. The operation principle and design procedure for the considered antenna are explained using equivalent circuits. In order to check the validity of this study, the results for reflection coefficients of the antenna obtained by the proposed equivalent circuit method and the simulation using commercial antenna design tool are compared with each other.

• Smart Structures and Systems
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• v.21 no.2
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• pp.195-205
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• 2018

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-reflecting boundaries were proposed in both numerical and experimental cases to facilitate time-frequency characterization of Lamb wave dispersion. First, the Lamb wave equations in isotropic and laminated materials were analytically solved. Second, the non-reflecting boundaries were used as a series of frames with gradually increased damping coefficients in finite element models to absorb waves at boundaries while avoiding wave reflections due to abrupt property changes of each frame. Third, damping clay was sealed at plate edges to reduce the boundary reflection in experimental test. Finally, the direct waves were subjected to the slant-stack and short-time Fourier transformations to calculate the dispersion curves of phase and group velocities, respectively. Both the numerical and experimental results suggest that the boundary reflections are effectively alleviated, and the dispersion curves generated by the time-frequency analysis are consistent with the analytical solutions, demonstrating that the combination of non-reflecting boundary and time-frequency analysis is a feasible and reliable scheme for characterizing Lamb wave dispersion in plate-like structures.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.11
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• pp.1473-1480
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• 1995

When the LMS algorithm is employed in the transversal filter structure, the computational complexity can be kept reasonably low. However, if the impulse response to be estimated is very long or signals involved are highly correlated like a speech the convergence speed becomes slow. The lattice filter is an excellent alternative to improve convergence speed since the lattice structure inherently has the orthogonal property among the backward prediction errors, but at the expense of the excessive computational load. If the input signal to be used can be sufficiently well modeled as a .RHO.-th order autoregressive(AR) process, the reflection coefficients after the .RHO.- th stage will be close to zero. Then, instead of employing the full lattice structure, the joint lattice filter structure can be implemented in conjunction with the transversal filter structure after the .RHO.-th stage. We propose, in this paper, this new lattice/transversal joint structure, and we will call it the reduced lattice filter. Using the reduced lattice filter, we are now able to achieve the performance as good as that of the lattice filter, while maintaining the complexity as low as that of the transversal filter. The proposed filter is particularly useful for an acoustic echo canceller due to the highly correlatedness nature of speeches and the long and frequently changing echo paths.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.47-52
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• 2002

It was virtually declared that measurement science must abandon the error analysis of measurement when ISO had published "Guide to Expression of uncertainty in Measurement" International inclination of measurement field in order to guarantee the traceability and confidence of measurement results discards the error concept and instead analyzes the measurement uncertainty. In this paper we establish a mathematical model of measurement and analyze all uncertainty factors as possible as for yielding the measurement uncertainty in the course of the calibration of RF multimeter using Transfer Standard, Thermal Voltage Converter We produce the expanded uncertainty by analyzing cable effects, correlation of thermocoupler and DC meter, DC source, RF source, attenuator, reflection coefficients and DUT.s and DUT.

• Journal of electromagnetic engineering and science
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• v.14 no.3
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• pp.293-298
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• 2014

Large spaceborne antennas should be lightweight, a factor related to the development costs of launch vehicles. In order to overcome this drawback, a feasibility study of a new carbon fiber reinforced polymer (CFRP) named M55J/RS3 is carried out for a synthetic aperture radar (SAR) reflector antenna. In particular, the high resolution of detected images is taken into consideration. To validate the electrical performance, a test of the CFRP specimen is fabricated, and the transmission/reflection coefficients are measured using a standard X-band waveguide. Finally, the effective complex permittivity and effective electrical conductivity are derived from the obtained measured data. By applying the derived conductivity to the simulation of the radiation pattern, antenna gain, and beamwidth-instead of relying on the assumption of a perfect electric conductor-variations in electrical performance are also investigated and discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1598-1603
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• 2003

A microstrip array antenna is designed and tested for satellite broadcasting receptions. The Sierpinski equilateral triangular patch and SSFIP(slot­strip­foam­inverted patch) structures are used. The Sierpinski geometry is composed of 3 equilateral triangular patch and is easy to generate a circular polarization by sequential rotation array techniques. This 1${\times}$3 Sierpinski equilateral triangular patch antenna is extended to 8${\times}$2 array antenna for satellite broadcasting receptions. The measurement results of the reflection coefficients and the radiation patterns of the manufactured array antenna show good agreements with the simulation results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1632-1638
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• 2008

This paper presents a method to design CPW (coplanar waveguide) balanced amplifiers using the existing CPW wilkinson balun. In order to realize the required power dividing/combining structure for balanced amplifiers, the CPP wilkinson balun is adopted. The proposed CPW balanced amplifier has much better matching performances than the CPW single-ended amplifier. The measured frequency bands, where the input and output reflection coefficients are less than -10dB, are $1.2{\sim}2.75GHz$ and $1{\sim}3.25GHz$, respectively, while the CPW single-ended amplifier has severely bad ones.