• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.716-723
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• 2011

The battery capacity of electric/hybrid vehicle is much larger than present automobile. For that reason, the connector of Green Car should be designed to transmit the high-electric voltage. In addition, the electromagnetic wave should be shielded to protect communication and signal circuits. In this study, shielding performance of the connector was analyzed through electromagnetic shield analysis, and a connector of Green Car was designed using thermoelectrical analysis, which is capable of transmitting the high-electric power. In the design of connector structure, the improved stability and workability was considered.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.534-544
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• 1997

The permittivity distribution of a two-dimensional high-contrast object with large size, which leads to the global minimum of cost function, is reconstructed by iteratively using the hybrid algorithm of Levenberg-magquardt algorithm(LMA) plus Genetic Algorithm(GA). The scattered fields calculated in a cost function are expanded in angular spectral modes, of which only effective propagating modes are used. The definition of cost function based on the effective propagating modes enables us to formulate the minimum number of incident waves for the reconstruction of object. It is numerically shown that LMA has an advantage of fast convergence but can't reconstruct a high-contrast object with large size and GA can reconstruct a high-contrast object with large size but has an disadvantage of slow convergence, whereas an inverse scattering technique using the hybrid algorithm adopts only advantages of LMA and GA.

• Korean Journal of Materials Research
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• v.12 no.2
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• pp.160-165
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• 2002

High-frequency dielectric and microwave absorbing properties have been investigated in ferroelectric materials (BaTiO$_3$(BT), (1-x)Pb$Mg_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O$_3$-xPbTiO$_3$(PMN-PT), (1-x)Pb$Mg_{\frac{1}{3}}Nb_{\frac{2}{3}}$O$_3$-xPb(Zn_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O$_3$(PMN-PZN) for the aim of thin microwave absorbers in the frequency range of mobile telecommunication. The specimenns are prepared by conventional ceramic processing and complex permittivity has been measured by transmission/reflection method. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave range and their domiant loss mechanism is considered to be domain wall relaxation. The microwave absorbance of BT 0.9PMN-0.1PT, and 0.8PMN-0.2PZN specimen (determined at 2) are found to be 99.5% (at a thickness of 4.5 mm), 50% (2.5 mm), and 30% (2.5 mm), respectively. It is suggested that PMN-PT or PMN-PZN ferroelectrics are good candidate materials for the spacer of λ/4 absorber. The use of ferroelectric materials is effective in reducing the thickness of absorber with their advantage of high dielectric constant.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.7
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• pp.432-436
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• 2017

IZO transistors with $Al_2O_3$ as gate dielectrics have been investigated. To improve permittivity in an ambient dielectric layer, we grew $Al_2O_3$ by atomic layer deposition directly onto the substrates. Then, we prepared IZO semiconductor solutions with 0.1 M indium nitrate hydrate [$In(NO_3)_3{\cdot}xH_2O$] and 0.1 M zinc acetate dehydrate [$Zn(CH_3COO)_2{\cdot}2H_2O$] as precursor solutions; the IZO solution made with a molar ratio of 7:3 was then prepared. It has been found that these oxide transistors exhibit low operating voltage, good turn-on voltage, and an average field-effect mobility of $0.90cm^2/Vs$ in ambient conditions. Studies of low-voltage driving of IZO transistors with atomic layer-deposited high-k $Al_2O_3$ as gate dielectric provide data of relevance for the potential use of these materials and this technology in transparent display devices and displays.

• Journal of electromagnetic engineering and science
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• v.17 no.4
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• pp.202-207
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• 2017

This paper presents the performance of a planar, low-profile, and wide-gain-bandwidth leaky-wave slit antenna in different thickness values of high-permittivity gallium arsenide substrates at terahertz frequencies. The proposed antenna designs consisted of a periodic array of $5{\times}5$ metallic square patches and a planar feeding structure. The patch array was printed on the top side of the substrate, and the feeding structure, which is an open-ended leaky-wave slot line, was etched on the bottom side of the substrate. The antenna performed as a Fabry-Perot cavity antenna at high thickness levels ($H=160{\mu}m$ and $H=80{\mu}m$), thus exhibiting high gain but a narrow gain bandwidth. At low thickness levels ($H=40{\mu}m$ and $H=20{\mu}m$), it performed as a metasurface antenna and showed wide-gain-bandwidth characteristics with a low gain value. Aside from the advantage of achieving useful characteristics for different antennas by just changing the substrate thickness, the proposed antenna design exhibited a low profile, easy integration into circuit boards, and excellent low-cost mass production suitability.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.285-290
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• 2007

Electrical and electromagnetic methods were widely applied to survey of civil engineering, environment site assessments and maintenance of underground structures in Korea. Electro-physical properties measurements of soil and rock are necessary in order to quantitatively estimate the ground from these survey results. A few geotechnical researcher groups have been simplified measurement system of the electro-physical properties, which was intermittently operating by the necessity. Recent strong concern about $CO_2$ underground storage and development of gas hydrate projects have urged many advanced countries. The electro-physical properties estimation of the deep object stratum is very importance for basic information of these research. So, advanced countries have a high-end measurement system with high temperature(200 degrees) and pressure(300 MPa), also they have been a lot of experience and know-how on the electro-physical properties measurement.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.437-438
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• 2007

In this paper a embedded decoupling capacitor design with gap structure will be discussed. A novel structure is modeling and analization by High Frequency Structure Simulator (HFSS). Proposed capacitor have $2m{\times}2m$ in rectangular shape. The film thickness of copper/dielectric film/substrate is respectively 35um/20um/35um. A dielectric layer of BaTiO3/epoxy has the relative permittivity of 25. Compare of the planar decoupling capacitor, capacitance densities of this structure in the range of $55{\mu}F$/mm2 have been obtained with 50um gap while capacitance densities of planar structure $55{\mu}F$/mm2 in the same size. The frequency dependent behavior of capacitors is numerically extracted over a wide frequency bandwidth 500MHz-7GHz. The decoupling capacitor can work at high frequency band increasing the gap size.

• Journal of the Korean Society of Radiology
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• v.16 no.6
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• pp.761-769
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• 2022

Pads with high dielectric materials have been used in a variety of applications to locally improve the field sensitivity and homogeneity of RF pulses in clinical MRI studies. In this study, we aimed to improve such pads in consideration of the practical problems associated with the application of actual clinical images. A high permittivity pad to increase the attenuated B1 field strength was fabricated and tested in 7T MRI. Sim4Life simulation and experimental results show stronger and relatively uniform B1 near field. In order to improve the image quality in the whole cerebellum, known as a region with low sensitivity, a guide was made to reduce the mechanical change of the pad. In order to improve the wearing comfort, the pad was designed by dividing it into upper and lower parts. The facial pad showed an overall signal increase effect in areas such as the turbinate in the nasal cavity. Signal increase was expected in areas such as the frontal lobe and eyes, but the effect was either insignificant or it was difficult to see the effect in the imaging protocol. In conclusion, this paper showed a cerebellar-optimized pad with an improved nasal signal while maintaining its effectiveness.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.308-313
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• 2015

This paper describes a technique for complete identification of a two-dimensional scattering object and multiple objects immersed in air using microwaves where the scatterers are assumed to be a homogenous dielectric medium. The employed technique consists of initially retrieving the shape and position of the scattering object using a linear sampling method and then determining the electric permittivity and conductivity of the scatterer using adjoint sensitivity analysis. Incident waves are assumed to be TM (Transverse Magnetic) plane waves. This inversion algorithm results in high computational speed and efficiency, and it can be generalized for any scatterer structure. Also, this method is robust with respect to noise. The numerical results clearly show that this hybrid approach provides accurate reconstructions of various objects.

• Applied Microscopy
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• v.47 no.3
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• pp.121-125
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• 2017

This study deals the prediction of temperature effect on low-frequency dispersion of alternating current (AC) conductivity spectra of composite materials based on copolymer reinforced with carbon black (CB) particles. A sample of ethylene butylacrylate loaded with 13% of CB particles were prepared and investigated using the impedance spectroscopy representation in the frequency range from 40 Hz to 0.1 MHz and temperature range from $20^{\circ}C$ to $125^{\circ}C$. The dielectric constant, ${\varepsilon}^{\prime}$, and dielectric losses, ${\varepsilon}^{{\prime}{\prime}}$, were found to decrease with increasing frequency. The frequency dependence of the AC conductivity follows the universal power law with a large deviation in the high frequency region, the positive temperature coefficient in resistivity effect has been observed below the melting temperature which makes this composite potentially remarkable for industrial applications.