• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.701-708
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• 2016

A new design for an ultra-wideband microstrip-to-FGCPW(Finite Ground Coplanar Waveguide) transition is presented. The proposed transition provides the electric field and impedance matching between adjacent transmission lines by ground shaping. The transition is designed on the analytical expressions of whole transitional structure. Conformal mapping is applied to obtain the characteristic impedance of FGCPW with bottom aperture within 3.3 % accuracy as compared with the EM-simulation results. As design example, the fabricated transition in back-to-back configuration provides insertion loss less than 1 dB per transition and return loss better than 10 dB for frequencies from 9 GHz to over 40 GHz.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.220-221
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• 2005

Sub-bottom profiler(SBP) has been used extensively for the mapping of basement in the foundation design of offshore structure, for pre- and post-dredging operations within harbors and channels, for selection of pipeline routes, sitting of drilling platforms, and in the exploration for an aggregates such as sands and gravels. During the construction of Siwha embankment for irrigation water and the expansion of arable land, the breaking of an embankment unfortunately occurred so that a lot of riprap was swept away and widely dispersed by the tide and strong current. The feasibility study for the construction of the tidal-powered electric plant in Siwha embankment was performed quite recently. Therefore we made use of SBP survey to investigate the distribution of the lost riprap. We could successfully map out the distribution of the lost riprap from the reflection amplitude characteristics of the sediments in SBP data set. We demonstrated the variation of reflection amplitude versus the sediments with and/or without riprap by means of the numerical modeling of acoustic wave equation using finite difference method. Also we examined an amplitude anomaly of the ripraped area through the physical modeling using ultrasonic.

• Journal of the Korean Institute of Telematics and Electronics
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• v.7 no.3
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• pp.12-18
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• 1970

In this paper, the radiation characteristics of a Circular Loop Antenna is studied in a moving homogeneous, isotropic and linear media with a constant velocity much less than the speed of light. In Stuffing the radiation characteristics, Srst vector potential on the loop antenna is derived in the moving media by appling Maxwell-Minkowaski's theory. Next, using the derived relations, the electric and magnetic Seld is calculated for the spec-i Sed wave length ana velocity of the media. The Seld patterns in the moving media are compared with those of stationary media. We find that the intensity of the field is reduced in the direction of the media velocity and increased in the opposite direction only for the component parallel with the plane of the antenna. The deviation from the stationary media is proportional to the velocity of the media and the frequency of source current.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1108-1114
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• 2016

The cause of failure in the AT feeding system is divided into grounding, short-circuit of feeding circuit and internal faults of the railway substation. Since the fault current is very high, real-time current is detected and the failure must be immediately removed. In this paper, a new DC offset elimination filter that can remove component to decrease in the form of exponential function using low-pass filter was proposed in order to extract the fundamental wave from distorted fault current. In order to confirm the performance of the proposed filter method, AT feeder system was modelled by simulation tool and simulations were performed under various conditions such as fault location, fault resistance and fault voltage phase angle in case of trolley-rail short-circuit fault. When applying the proposed DC-offset removal method, it can be seen that the phase delay and gain error did not appear.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.113-118
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• 2009

Grounding systems set the reference voltage level of electric circuits and suppress the Ground Potential Rise (GPR) by flowing fault currents to the ground safely. There are several parameters which evaluate the performance of grounding systems as ground resistance, touch voltage and step voltage. The touch and step voltages, which is called "risk voltage", are especially important to ensure the safety of human body. This paper dealt with the influence of current sources with the different frequency components on the touch and the step voltages. Three types of current sources as commercial frequency, square wave, and surge with the fast risetime of $50\;ns{\sim}500\;ns$ were used to analyze the risk voltages in a grounding system. The risk voltages showed remarkable difference in the same current amplitude depending on the current sources, and increased linearly with the current amplitude in the same current source. From the experimental results, it was confirmed that the risk voltages can be evaluated by a small current application in large-scale grounding systems and the possible largest risk voltage can be calculated by a surge current with the risetime of 200 ns or a current source with the same frequency component as the surge current.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.4
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• pp.73-79
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• 2002

In this paper, electromagnetic waves radiated from discharge at three-type electrodes(needle-plane, plane-plane and sphere-plane electrode) using AC power source in air are measured and the peculiar patterns of their spectra are reported. The radiated electromagnetic waves were measured in bandwidth of VHF(30-230[MHz]) using a biconical antenna and a spectrum analyzer. When the discharge onset voltage range, high electric field intensity is shown in frequency band of 45, 70, 80[MHz] in case of needle-plane electrode configuration and 40[MHz] in case of plane-plane and sphere-plane electrodes configuration. However, when the breakdown voltage range, the frequency spectrum distribution of radiated electromagnetic waves appear different in the whole frequency range according to the shapes of electrode.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.3
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• pp.261-264
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• 2009

We present a three-dimensional (3D) particle focusing channel using the positive dielectrophoresis (pDEP) guided by a dielectric structure between two planar electrodes. The dielectric structure between two planar electrodes induces the maximum electric field at the center of the microchannel, and particles are focused to the center of the microchannel by pDEP as they flow from the single sample injection port. Compared to the previous 3D particle focusing methods, the present device achieves the simple and effective particle focusing function without any additional fluidic ports and top electrodes. In the experimental study, approximately 90 % focusing efficiency were achieved within the focusing length of 2mm, on both x-z plane (top-view) and y-z plane (side-view) for $2{\mu}m$-diameter polystyrene (PS) bead at the applied voltage over 15 Vp-p (square wave) and at the flow rate below 0.01 ${\mu}l$/min. The present 3D particle focusing channel results in a simple particle focusing method suitable for use in integrated microbiochemical analysis system.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.246-248
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• 2002

This paper presents a high-frequency voltage source inverter for silent corona discharge ozonizer application, which is characterized by the power control based on pulse density modulation (PDM). The PDM inverter produces either a square -wave ac-voltage state or a zero-voltage state at its ac terminals to control the average output voltage under constant do voltage and operating frequency. This results in a wide range of power control in the silent corona discharge load with a strong nonlinear characteristics. And proposed addition circuit for maintain discharge on the center of the airgap. In this paper, schemed equivalent electric circuit of the discharge electrode for simulation. Finally, the effectiveness of this discharge tube character of silent corona ozonizer is investigated in the simulation results.

• Composites Research
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• v.17 no.5
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• pp.68-77
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• 2004

The electromagnetic (EM) absorption or shielding characteristics of a material is an important issue not only for military purpose but also for commercial purposes such as radar, electric or telecommunication devices. In order to design the effective electromagnetic wave absorber, the electromagnetic characteristics of the constituents of the material should be available in target frequency band. Also, it must be possible to predict the electromagnetic properties of absorbers with respect to the content of lossy ingredients. In this study, the dielectric properties of unsaturated polyester resins containing nano-size conductive carbon black powder were measured with a free space method in the X-band frequency range and analyzed with respect to the content of carbon black. Finally, the method for estimating the dielectric properties of polymeric resin containing conductive carbon black with respect to the EM frequency was developed and verified.

• Journal of Broadcast Engineering
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• v.2 no.1
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• pp.1-7
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• 1997

In this paper, a microstrip patch antenna was analyzed by using FDTD method. Firstly, the electric field in the microstrip patch antenna was obtained by approximating a Maxwell's equation to a finite difference equation by means of Yee's algorithm. In this case, Mur's 1st approximation and dispersive boundary condition(BBC) were applied to an absorbing boundary condition. We also analyzed a single microstrip patch antenna by using the FDTD method, then calculating the propagative process in the wave of a return loss. Also, as the result that FDTD was applied to 2-array antenna designed to increase the gain of antenna, the measured results was in relatively good accordance with the values calculated by the FDTD method. The calculated impedance, return loss and VSWR were comparatively good. And these results were In relatively good accordance with the measured values.