• 한국전기전자재료학회논문지
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• 제13권10호
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• pp.887-894
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• 2000

In this paper, we have studied the effect of earth (Gd, Er) on the various properties (microstructure, shrinkage, initial permeability, permeability as a function of frequency, etc) of Ba-ferrite. The permeabilities were analyzed by Impedance Analyzer(100KHz~40MHz) and Network Analyzer(30KHz~3㎓). As the result of XRD, all of the Ba-ferrite doped with rat earth was found to be Y-hexagonal phase. The resonance frequencies at the maximum imaginary value of complex permeability were observed near 2㎓. The complex permeabilities of the Ba-ferrite doped with Gd$_2$O$_3$at 3wt% and doped with Er$_2$O$_3$at 3wt% and 5wt% as a function of frequency showed the highest value at sintered temperature at 95$0^{\circ}C$/3h.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.89-92
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• 1999

NCZF ferrites doped with B-Bi-Zn(35-25-40) glass ceramics were prepared to investigate the magnetic properties. The XRD peaks of all of samples were observed only spinel phase. As the additive increased at sintering temperature 750$^{\circ}C$ and 850$^{\circ}C$ for 3 hours, the density and shrinkage increased until 5.28g/㎤ and 20%, respectively. According to SEM images, the growth of grain progressed rapidly at sintering temperature 850$^{\circ}C$ for 3 hours. Increasing the additive, initial permeability and complex permeability decreased. The complex permeabilities as a function of frequency showed high values at a12, a16, b11 and b16 sarmples.

• 항공우주시스템공학회지
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• 제17권1호
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• pp.42-50
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• 2023

본 연구에서는 SrZn_2-xCo_xFe₁₆O₂₇ 화학식을 갖는 육방정 구조의 페라이트 분말을 고상법으로 합성하고 Co-Zn 함량 변화에 따른 전자기파 흡수 특성을 0.1-18 GHz의 주파수 범위와 0 ~ 10 mm 흡수체 두께 범위에서 평가하였다. 흡수체 두께에 따른 전자기파 흡수 특성은 고주파 복소 투자율과 유전율 측정 data로부터 전송선 이론을 기반으로 계산을 통해 반사손실 (RL)을 도출하였으며, 일부 시료에 대해서는 RL 실측정을 통해 계산된 결과와 잘 맞는 것을 보였다. Co의 치환량 (x)에 따라 고주파 복소 투자율 특성이 변화하였으며 이에 따라 전자기파 흡수 주파수 대역의 조절이 가능하였다. 또한 x = 1.0, 1.25, 1.5 시료에서는 매우 우수한 최대 전자기파 흡수 특성 (RL = -70 ~ -50 dB )을 보이며, 90% 이상의 전자기파 에너지를 흡수 (RL ≤ -10 dB) 하는 주파수 밴드 폭 또한 10 GHz 이상으로 광대역 레이다 흡수가 가능함을 보였다.

• 폴리머
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• 제38권2호
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• pp.232-239
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• 2014

용액 삽입(solution intercalation) 방법을 이용하여 다양한 나노 필러들을 포함하는 poly(lactic acid)(PLA) 나노 복합체를 합성하였다. 유기화 반응 처리된 벤토나이트 점토(NSE), 옥타데실아민(ODA)을 산화 그래핀(GO)에 반응한 ODA-GO, 그리고 유기화 처리된 벤토나이트와 ODA-GO의 복합체인 NSE/ODA-GO 등이 PLA 복합체 필름을 얻기 위한 나노 필러로 각각 사용되었다. 3가지 나노 필러들은 0-10 wt%의 함량으로 사용되었고 PLA 복합체 필름들의 열적-기계적 성질, 모폴로지, 산소 투과도 결과들을 서로 비교하였다. 투과전자현미경을 통하여 얻은 결과에서 NSE/ODA-GO 복합체는 약간 뭉쳐있었지만, NSE나 ODA-GO 등의 필러들은 PLA 매트릭스에 분산이 매우 양호하였음을 알 수 있었다. PLA 복합체 합성을 위해 사용된 3가지 필러 중에서, 열적 안정성에서는 NSE/ODA-GO가 가장 효과적이었지만, 기계적 인장 성질이나 산소 차단성에서는 각각 NSE와 ODA-GO가 가장 우수하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.597-599
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• 1992

A calculation method for predicting the instantaneous torques by the inductance profiles of a switched reluctance motor (SRM) is presented. The method considers saturation and nonlinearities in the magnetic circuits. The inductance of SRM varies complex according to the input current waveforms and rotor position angle, thus the accurate calculation technique is needed to estimate the inductance value at arbitary input current and rotor position angle. This paper describes how the inductance profiles influence the torque produced by the input current of SRM and, proposes a calculation technique of the permeabilities, reluctances, current waveforms and torques of a 6/4 3-phase SRM.

• Smart Structures and Systems
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• 제7권3호
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• pp.199-211
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• 2011

Using computational modeling, we design a pair of biomimetic microcapsules that exploit chemical mechanisms to communicate and alter their local environment. As a result, these synthetic objects can undergo autonomous, directed motion. In the simulations, signaling microcapsules release "agonist" particles, while target microcapsules release "antagonist" particles and the permeabilities of both capsule types depend on the local particle concentration in the surrounding solution. Additionally, the released nanoscopic particles can bind to the underlying substrate and thereby create adhesion gradients that propel the microcapsules to move. Hydrodynamic interactions and the feedback mechanism provided by the dissolved particles are both necessary to achieve the cooperative behavior exhibited by these microcapsules. Our model provides a platform for integrating both the spatial and temporal behavior of assemblies of "artificial cells", and allows us to design a rich variety of structures capable of exhibiting complex dynamics. Due to the cell-like attributes of polymeric microcapsules and polymersomes, material systems are available for realizing our predictions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.205-208
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• 1999

We have studied properties(crystal structure, density, absorption, contraction, initial permeability, and permeability) of Ba$\sub$0.2/Me$\sub$0.31/Fe$\sub$0.49/(Me:Ni$\sub$1-x/, Cu$\sub$x/ x=0~1) ferrites with various Me site, because of development of magnetic materials for inductor. As a results of the density, absorption rate, and shrinkage rate, the sintering temperature of Ba$\sub$0.2/ Me$\sub$0.31/ FEesub 0.49/(Me:Ni$\sub$1-x/ x=0.25, 0.75) had got over 1100$^{\circ}C$ for 3 hours. According to SEM images, the configurations of grain were hexagonal, Increasing the sintering temperature, initial Permeability increased. The complex permeabilities as a function of for several MHz showed constants.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.204-207
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• 2000

In this paper, we have studied the effect of doped with B-Bi-Zn on properties (microstructure, density, shrinkage, permeability as a function of frequency, etc.) of hexagonal-ferrite for high frequency chip-inductor material about several GHz. The permeability were analyzed by impedance analyzer(100 kHz~40 MHz) and network analyzer(30 MHz~3 GHZ). As a result of the characteristics, the B-Bi-Zn glass ceramic was used to lower the sintering temperature for additive as a function of frequency from 100 kHz to 1.8 GHz showed constant tends. The maximum imaginary value of complex permeability was observed near the resonance frequency of 2 GHz.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.244-251
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• 2009

Porous media have especially large surface area per volume, which contain complex fluid passage. If porous media can be applied to cool a CPU or an electronic device with large heat dissipation, it could result in heat transfer enhancement due to the enlargement of the heat transfer area and the flow disturbance. This study is aimed to identify the heat transfer and pressure drop characteristics of high-porosity metal foams in a horizontal channel. Experiment is performed with the various heat flux, velocity and pore density conditions. Permeabilities, which is deduced from Non-Darcy flow model, become lower with increasing pore density. Nusselt number also decreases with higher pore density. High pore density with same porosity case shows higher pressure loss due to the increase of surface area per unit volume. The fiction factor decreases rapidly with increase of Reynolds number in Darcy flow region. However, it converges to a constant value of the Ergun coefficient in Non-Darcy flow region.

• 한국자기학회지
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• 제12권5호
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• pp.195-200
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• 2002

각종 산화물을 첨가하여 Co$_2$Z type Ba-ferrite의 저온소결에 관하여 연구하였다. Co$_2$Z type Ba-ferrite 상은 2회 하소과정을 통하여 얻을 수 있었으며, 생성된 상의 XRD peaks는 일부 minor peaks 제외하고는 standard peaks와 거의 일치하였다 제조된 분말은 저온소결을 위하여 ZnO-B$_2$O$_3$ glass리 단독 첨가 및 CuO 또는 Bi$_2$O$_3$와 복합 첨가하였으며, 또한 ZnO-Bi$_2$O$_3$ glass를 단독 첨가하였다. 소결은 900~100$0^{\circ}C$에서 수행하였다. ZnO-B$_2$O$_3$ glass의 단독 첨가 시, 첨가량이 7.5 wt%일 때 가장 높은 수축거동을 나타내었다. ZnO-Bi$_2$O$_3$ glass와 CuO 또는 Bi$_2$O$_3$를 복합 첨가하였을 때, glass를 단독 첨가하였을 경우보다 수축률이 급격히 증가되었다. 또한 ZnO-Bi$_2$O$_3$ glass를 단독 첨가한 시편의 수축률과 초기 투자율은 ZnO-B$_2$O$_3$ glass를 단독 첨가한 시편보다 높은 값을 나타내었다.