• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.2
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• pp.195-200
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• 2020

Leakage and Bragg condition of optical waveguides with blazed grating profile are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. The blazed waveguides classified as symmetric, sawtooth and asymmetric gratings occur leaky-wave stop-band at Bragg conditions and anomalies based on Rayleigh condition near Bragg conditions. Furthermore, DFB properties of blazed waveguides at Bragg conditions are analyzed by applying longitudinal equivalent transmission-line with characteristic impedance of periodic grating. The numerical results show that the reflected power of DFB waveguides is maximized at Bragg conditions in which leaky-wave stop-bands occur.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.49-57
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• 2022

The interaction of planar shock wave with rectangular water column is investigated numerically. The flow phenomenon like reflection, transmission, cavitation, recirculation of shock wave, and large negative pressure due to expansion waves was discussed qualitatively and quantitatively. The numerical simulation was performed in a shock tube with a water column, and planar shock was initiated with a pressure ratio of 10. Three cases of the water column with different thicknesses, namely 0.5D, 1D, and 2D, were installed and studied. Water naturally has a higher acoustic impedance than air and mitigates the shock wave considerably. The numerical simulations were modelled using Eulerian and Volume of fluids multiphase models. The Eulerian model assumes the water as a finite structure and can visualize the shockwave propagation inside the water column. Through the volume of fluids model, the stages of breakup of the water column and mitigation effects of water were addressed. The numerical model was validated against the experimental results. The computational results show that the installation of a water column significantly impacts the mitigation of shock wave.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.837-841
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• 2008

Propulsion of gene coated micro-particles is desired for non-intrusive drug delivery inside biological tissue. This has been achieved by the development of a device that uses high power laser pulses. The present paper looks at the mechanisms of micro-particle acceleration. Initially, a high power laser pulse is focused onto the front side of a thin aluminium foil leading to its ablation. The ablation front drives a compression wave inside the foil, thus leading to the formation of a shock wave, which will later reflect from the rear side of the foil, due to acoustic impedance mismatch. The reflected wave will induce an opposite motion of the foil, characterized by a very high speed, of the order of several millimeters per microsecond. Micro-particles, which are deposited on the rear side of the foil, thus get accelerated and ejected as micro-projectiles and are able to penetrate several hundreds of micrometers inside tissue-like material. These processes have been observed experimentally by using high-speed shadowgraphy and considered analytically.

• Geophysics and Geophysical Exploration
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• v.7 no.4
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• pp.234-244
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• 2004

In order to calculate 3-dimensional wavefield using finite-element method in frequency domain, we must factor so huge sparse impedance matrix. Because of difficulties of handling of this huge impedance matrix, 3-dimensional wave equation modeling is conducted mainly in time domain. In this study, we simulate the 3-D wavefield using finite-element method in Laplace domain by combining high-performance parallel finite-element solver and SWEET (Suppressed Wave Equation Estimation of Traveltime) algorithm which can calculate the traveltime and the amplitude. To verify this combination, we applied it to the SEG/EAGE 3D salt model in serial and parallel computing environments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.8
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• pp.67-78
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• 2009

Radiation characteristics of microstrip patch antennas integrated with mushroom-like EBG structures in all directions and length direction on a substrate with the relative dielectric constant of 10 are systematically analyzed. As the substrate thickness increases, the effect of the surface wave on the input impedance and radiation pattern of a patch antenna increases. The effect of EBG structures on the input impedance of a patch antenna is negligible when the distances between EBG structures and the center of a patch antenna are 0.4 ${\gamma}_0$, 0.2 ${\gamma}_0$ and 0.1 ${\gamma}_0$ for the substrate thickness of 3.2 mm, 1.6 mm and 0.8 mm, respectively. The forward radiation is improved due to the suppression of surface wave when the periods of EBG structures integrated are larger than 2, 2, 3 periods for the substrate thickness of 3.2 mm, 1.6 mm and 0.8 mm, respectively. The effects of EBG structures on the radiation characteristics of a patch antenna integrated with EBG structures in all directions and length direction are similar.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.3
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• pp.41-48
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• 2002

The bandwidth limitation of traveling-wave electroabsorption modulator(TW-EAM) is determined by the transit time, the velocity-mismatch between optical-wave and microwave, the impedance-matching, the dispersion and the microwave loss. In this paper, we introduce an hovel impulse response of TW-EAM considering transit time as well as velocity-mismatch. We analyze the effect of transit-time and velocity-mismatch at the same time, using the FDTD method. We investigate the modulation bandwidth by changing the depth of the intrinsic region. We suggest that the optimum depth of the intrinsic region is 0.2${\mu}{\textrm}{m}$ when the absorption coefficient($\alpha$) is 0.2${\mu}{\textrm}{m}$-1.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.587-595
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• 1997

Experimental study on unsaturated flow in the soil is important to understand the characteristics of the water flow. Measurement of unsteady-state water movement using the traditional equipment (e.g. tensiometer) has a problem that requires relatively a long response time. In this study a quick measurement method of soil water flow using TDR is introduced. TDR consists of an electronic function generator which generates a squared wave, and an oscilloscope which catches the reflected wave. The wave is reflected where both the impedance of the transmission line and the propagation velocity are changed. The water content can be obtained from the travel time measured by means of TDR because the dielectric constant is affected by the change of soil water content. From the result of TDR calibration. TDR measurement error for the oven dried soil was found to be less than 3.5%. This supports that TDR is a viable technique to measure the unsteady-state water movement.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.3 s.357
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• pp.26-34
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• 2007

This Paper describes a chip design technique for body composition analyzer based on the BIA (Bioelectrical Impedance Analysis) method. All the functions of signal forcing circuits to the body, signal detecting circuits from the body, Micom, SRAM and EEPROMS are integrated in one chip. Especially, multi-frequency detecting method can be applied with selective band pass filter (BPF), which is designed in weak inversion region for low power consumption. In addition new full wave rectifier (FWR) is also proposed with differential difference amplifier (DDA) for high performance (small die area low power consumption, rail-to-rail output swing). The prototype chip is implemented with 0.35um CMOS technology and shows the power dissipation of 6 mW at the supply voltage of 3.3V. The die area of prototype chip is $5mm\times5mm$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.118-124
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• 2015

The design of radar absorbing structures(RAS) is a discrete optimization problem and is usually processed by stochastic optimization methods. The calculation of radar cross section(RCS) should be decreased to improve the efficiency of designing RAS. In this paper, an efficient method using impedance matching is studied to design RAS for minimizing RCS. Input impedance of the minimal RCS for the specified wave incident conditions is obtained by interlocking physical optics(PO) and optimizations. Complex permittivity and thickness of RAS are designed to satisfy the calculated input impedance by a discrete optimization. The results reveal that the studied method attains the same results as stochastic optimization which have to conduct numerous RCS analysis. The efficiency of designing RAS can be enhanced by reducing the calculation of RCS.

• ETRI Journal
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• v.35 no.5
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• pp.827-837
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• 2013

In this paper, we present wideband common-mode (CM) noise suppression using a vertical stepped impedance electromagnetic bandgap (VSI-EBG) structure for high-speed differential signals in multilayer printed circuit boards. This technique is an original design that enables us to apply the VSI-EBG structure to differential signals without sacrificing the differential characteristics. In addition, the analytical dispersion equations for the bandgap prediction of the CM propagation in the VSIEBG structure are extracted, and the closed-form expressions for the bandgap cutoff frequencies are derived. Based on the dispersion equations, the effects of the impedance ratio, the EBG patch length, and via inductances on the bandgap of the VSI-EBG structure for differential signals are thoroughly examined. The proposed dispersion equations are verified through agreement with the full-wave simulation results. It is experimentally demonstrated that the proposed VSI-EBG structure for differential signaling suppresses the CM noise in the wideband frequency range without degrading the differential characteristics.