• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.647-652
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• 2015

A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

• Smart Structures and Systems
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• 제12권5호
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• pp.523-545
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• 2013

Piezoelectric and dielectric behaviors of a piezoceramic patch adhesively centered on a carbon composite plate are identified using a robust multi-objective optimization procedure. For this purpose, the patch piezoelectric stress coupling and blocked dielectric constants are automatically evaluated for a wide frequency range and for the different identifiable behaviors. Latters' symmetry conditions are coded in the design plans serving for response surface methodology-based sensitivity analysis and meta-modeling. The identified constants result from the measured and computed open-circuit frequencies deviations minimization by a genetic algorithm that uses meta-model estimated frequencies. Present investigations show that the bonded piezoceramic patch has effective three-dimensional (3D) orthotropic piezoelectric and dielectric behaviors. Besides, the sensitivity analysis indicates that four constants, from eight, dominate the 3D orthotropic behavior, and that the analyses can be reduced to the electromechanically coupled modes only; therefore, in this case, and if only the dominated parameters are optimized while the others keep their nominal values, the resulting piezoelectric and dielectric behaviors are found to be transverse-isotropic. These results can help designing piezoceramics smart composites for various applications like noise, vibration, shape, and health control.

• 대한전자공학회논문지
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• 제25권1호
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• pp.1-7
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• 1988

A new type broadband channel dropping filter which has a potential use as a millimeter-wave multiplexer has been realized by properly connecting 3-dB directional couplers and bandstop filters. 90\ulcorner3-dB directional couplers have been designed using two nonuniformly coupled dielectric image guides, while bandstop filters with Chebyshev passbands have been designed using dielectric image-guide grating structure. Effective dielectric constant method has been aplied to the image-guide dispersion analysis and to the design of bandstop gratings and 3-dB couplers. Experimental results in excellent agreement with computed responses are demonstrated.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2003년도 추계학술발표회
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• pp.289-292
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• 2003

Laboratory tests were performed to investigate the dielectric property of saturated sands contaminated by heavy metals solution at low frequency. Differences of contamination and the real part of dielectric constant depend on heavy metal concentration was measured at low frequency, 100KHz below. The optimal frequency to develop the detection potentials of monitoring was 1KHz, 10KHz, 100KHz. At this frequency, Heavy metal contamination of saturated sands contamination can be recommended by analysis of complex dielectric constant.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(I)
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• pp.119-122
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• 1987

By cascading the step discontinuities on planar dielectric waveguides with a ferrite layer through two uniform planar dielectric waveguides, nonreciprocal scaterring characteristics of planar dielectric waveguide gratings are analyzed. The calculated results at 35GHz shows that the isolation mechanism takes place near band stop frequency range.

• 대한전자공학회논문지
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• 제24권1호
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• pp.15-19
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• 1987

Bandstop characteristics of dielectric waveguide gratings are investigated using the modal approach. First, single step discontinuity of the dielectric waveguide is analyzed in terms of the mode matching method. Then by cascading those discontinuities characteristics of dielectric waveguide gratings are derived. Experimental results at X-band show good agreement with theoretical ones.

• 전자공학회논문지A
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• 제29A권11호
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• pp.57-61
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• 1992

In this paper, the shielding characteristics of a cylindrical multilayered dielectric are analyzed. In order to evaluate shielding effects, we consider the case that plane waves are incident upon an infinitely long cylindrical multilayered dielectric which surrounds a conductor core. For perfect and lossy dielectric distributions, total induced currents at the conductor surface are computed. It was found from those results that electromagnetic characteristics of the multilayered dielectric are largely dependent on dielectric distribution.

• 한국위성정보통신학회논문지
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• 제3권1호
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• pp.35-40
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• 2008

본 논문에서는 위성용 전자 부품 또는 장비를 내장한 함체의 개구가 유전체로 막힌 경우 차폐효과를 계산하는 해석적 방법을 제안한다. 차폐효과는 주파수, 유전체의 유전율, 함체 내에서 차폐효과를 정의하는 위치에 영향을 받는다. 또한, 유전체 판의 일부가 도체로 막혀 있는 경우도 해석하였다. 계산 결과를 보면, 유전체에 의하여 함체 공진의 Q 값이 감소되었으며, 개구에서 멀어질수록 차폐효과 개선되는 것을 확인 할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 연구회
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• pp.114-117
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• 2001

$(Ba_{0.6-x}Sr_{0.4}Ca_x)TiO_3$(x=0.10, 0.15, 0.20) ceramics were fabricated by the mixed-oxide method and their structural and dielectric properties were investigated with variation of composition ratio and sintering temperature. As a result of the differential thermal analysis(DTA), exothermic peak was observed at around $1020^{\circ}C$ due to the formation of the polycrystalline perovskite phase. BSCT(50/40/10) specimen sintered at $1500^{\circ}C$ showed the highest average grain size(18.25$[{\mu}m]$). Curie temperature and dielectric constant at room temperature decreased with increasing amount of Ca. BSCT(50/40/10) specimen sintered at $1450^{\circ}C$ showed a good dielectric constant, K, (=4324) and dielectric loss, $tan{\delta}$, (=0.972%) properties at 1[KHz].

• Transactions on Electrical and Electronic Materials
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• 제13권6호
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• pp.322-325
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• 2012

Crystalline silica was synthesized by annealing amorphous silica at $1,300^{\circ}C$ or $1,400^{\circ}C$ for various times, and the crystallinity was estimated by X-ray diffraction (XRD) analysis. In order to prepare a low dielectric material, epoxy/crystalline silica composites were prepared, and the effect of silica content on the dielectric properties was studied under various functions of frequency and ambient temperature. The dielectric constant decreased with increasing crystalline silica content in the epoxy composites, and it also decreased with increasing frequency. At 120 Hz, the value of 5 wt% silica decreased by 0.25 compared to that of 40 wt% silica, and at 23 kHz, the value of 5 wt% silica decreased by 0.23 compared to that of 40 wt% silica. The value increased with increasing ambient temperature.