• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.90-93
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• 1999

We present a high frequency electromagnetic (EM) inversion scheme for detecting and characterizing a fracture using single-hole data. At high frequencies, say above tens of mega-hertz, since displacement currents cannot be ignored, electrical permittivity as well as electrical conductivity is to be considered together for analyzing the EM scattering data. In this paper, we have developed a three-step inversion scheme to map the fracture and to evaluate its electrical conductivity and permittivity. We performed EM profiling along the z-axis using three-component receivers for each source. The model was excited by a vertical magnetic dipole and the resistant magnetic fields were inverted using the non-linear least-squares method. Background resistivity and permittivity were easily obtained using vertical magnetic fields below 1 MHz and above 10 MHz, respectively. Both the vertical and dipping sheets were successfully mapped using the phase difference between 40 and 41 MHz. The electrical property of the sheet was well resolved using the information obtained in the previous two steps and secondary magnetic fields. Our study shows the potential of imaging the fracture in single-hole survey environment using the high frequency EM method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.53-56
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• 2003

In this paper we investigated electrical properties for epoxy resin with improved mechanical property, elastomer epoxy. Investigated electrical properties are permittivity, tan $\delta$ and breakdown voltage strength(BDV). Permittivity and tan $\delta$ have dependancy on additive Quantity in general purpose epoxy resin. In particularly, those have very high values at low frequency and high temperature according to increasing component of elastomer. In case of BDV test, those materials have only a little difference due to increasing elastomer components. But in case of high quantities of elastomer, BDV has a difference. These results are represented that elastomer epoxy resin despite superior mechanical property needs many carefully thought as application electrical insulation.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1293_1294
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• 2009

The sintering and high frequency electro-magnetic properties of Ba-hexagonal ferrite were investigated. All samples of the Ba-hexagonal ferrite were prepared by the conventional mixed oxide method and sintered at $1150^{\circ}C$~$1400^{\circ}C$. From the X-ray diffraction patterns of sintered Ba-hexagonal ferrite, the $Ba_3Co_2Fe_{24}O_{41}$ phase was represented as main phase in the almost sintering conditions. The bulk densities with sintering temperature and decreased at $1400^{\circ}C$. The permittivity ($\varepsilon$') and loss tangent of permittivity ($\varepsilon$"/$\varepsilon$') of $Ba_3Co_2Fe_{24}O_{41}$ ceramics increased and decreased with sintering temperature, respectively. The permeability of $Ba_3Co_2Fe_{24}O_{41}$ ceramics decreased with sinteirng temperature. The loss tangent of permeability was not changed compared each other with sintering temperature. The bulk density of $Ba_3Co_2Fe_{24}O_{41}$ ceramics sintered at $1300^{\circ}C$ was 4.79 g/$cm^3$. The permittivity, loss tangent of permittivity and permeability, loss tangent of permeability were 19.896, 0.1718 and 14.218, 0.2046 at 210 MHz, respectively.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1697-1704
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• 2018

As a key component of lighting location system (LLS) for lightning warning, the atmospheric electric field measuring is required to have high accuracy. The Conventional methods of the existent electric field measurement meter can only detect the vertical component of the atmospheric electric field, which cannot acquire the realistic electric field in the thunderstorm. This paper proposed a three dimensional (3D) electric field system for atmospheric electric field measurement, which is capable of three orthogonal directions in X, Y, Z, measuring. By analyzing the relationship between the electric field and the relative permittivity of ground surface, the permittivity is calculated, and an efficiency 3D measurement model is derived. On this basis, a three-dimensional electric field sensor and a permittivity sensor are adopted to detect the spatial electric field. Moreover, the elevation and azimuth of the detected target are calculated, which reveal the location information of the target. Experimental results show that the proposed 3D electric field meter has satisfactory sensitivity to the three components of electric field. Additionally, several observation results in the fair and thunderstorm weather have been presented.

• Journal of Navigation and Port Research
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• v.34 no.2
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• pp.111-115
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• 2010

In this paper, the electromagnetic (EM) wave absorbers using TiO2 as a dielectric material with chlorinated polyethylene (CPE) were investigated in W-band radio frequencies. We compared the relative permittivity with reflectionless curve and the absorption properties of samples containing 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.%, and 80 wt.% TiO2. It is possible to realize a complex relative permittivity satisfying the reflectionless condition by choosing composition ratio of TiO2. The optimized composition ratio of TiO2 for the maximum absorption property is about 70 wt.%. As a result, we have confirmed the realization of an EM wave absorber with a high absorption property in W-band radio frequencies.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.8
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• pp.461-465
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• 2004

This paper analysed the induced current density by electric field of human body under the 765 kV transmission line considering permittivity and conductivity. As permittivity of human body is very high as $10^6$ at 60 Hz, special numerical computation technique in Surface Charge Method(SCM) for composite media with extremely different properties is applied to reduce calculation error of induced current density and electric field inside the human body. Calculation results show that the average of the induced current density inside human body is about 3mA/$m^2$, which is less than ICNIRP criterion (10mA/$m^2$).

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.6
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• pp.341-345
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• 2000

This paper analysed the induced electric field of human body under the 765 kV transmission line considering permittivity and conductivity. As permittivity of human body is very high as 106 at 60 Hz, special numerical computation technique is Surface Charge Method(SCM) for composite media with extremely different properties is applied to reduce calculation error of induced electric field inside the human body.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.69-77
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• 1996

We analyzed wideband propagation characteristics of a microstrip transmission line based on FR-4 composite substrate using the wideband complex dielectric constant model and the phenomenological loss equivalence method. The loss calculated by constant relative permittivity and loss tangent is greatly overestimatd compared to that calculated by the frequency-dependent complex relative permittivity. This wideband analysis can be helpful to characterize high-speed and high-density transmission lines associated with the wideband dielectric characteristics and shows that the FR-4 composite substrate has high potential of high frequency circuit applications in terms o fthe propagation loss.

• Ceramist
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• v.22 no.2
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• pp.110-121
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• 2019

Triboelectric nanogenerators and piezoelectric nanogenerators are a spotlighted energy harvesting method that converts the wasted mechanical energy from the environment into usable electrical energy. In the case of triboelectric nanogenerators, researches have been mainly focused on high permittivity and flexible polymer materials, and in the case of piezoelectric nanogenerators, researches have been focused on ceramic materials exhibiting high polarization characteristics. Recently, many researches have been conducted to improve durability and power in various environments by using composite materials which have flexible properties of polymer, high permittivity, thermal resistance and high polarization properties of ceramics. This article reviews the energy harvesting studies reported about composites materials using ceramics and polymers.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.231-241
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• 2005

Laboratory experiments were performed to examine the effects of water content and to see if permittivity had sufficient sensitivity to identify subsurface contamination. Both real and imaginary permittivities of unsaturated sand were strongly governed by the volumetric water content. Especially, a linear relationship between real permittivity and volumetric water content was derived at high frequencies (MHz ranges). Heavy metals in pore fluid result in significant increases in the effective imaginary permittivity, due to ionic conduction, but decreases in the real permittivity arises due to the decreased orientational polarization of water molecules caused by hydration of ions. Clear increase in the effective imaginary permittivity with heavy metal concentration was found to be valuable in the application of electrical methods for detecting heavy metals in the subsurface. However, because the permittivity is primarily dependent on the volumetric water content of soil, pre-evaluation on the volumetric water content is required.