• 한국재료학회지
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• 제7권9호
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• pp.758-762
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• 1997

52mol% Fe$_{2}$O$_{3}$, 26mol% MnO의 조성에서 calcium과 vanadium의 동시첨가에 의한 투자율의 변화원인을 살펴보았다. 초투자율은 첨가물의 농도가 커짐에 따라 감사하였으나 소결체의 밀도나 입자크기는 증가하였으므로 초투자율의 변화는 미세구조의 변화로는 설명되지 않았다. 전기비저항은 첨가물의 농도가 증가함에 따라 증가하였으며 이는 입계의 고저항층의 생성과 vanadium ion에 의한 Fe$^{2+}$이온의 산화로 설명되었다. 첨가물의 농도가 증가함에 따라, 초투자율의 제 2차 최대치가 나타나지 않는 것과 초투자율이 감소하는 것으로부터, 결정자기이방성 상수의 값은 음으로 커짐을 알 수 있었다. 투자육의 온도의존성과 비저항의 변화로부터, 첨가물의 농도에 따른 상온 초투자율의 감소는 Fe$^{2+}$ 이온 농도의 감소에 따른 결정자기이방성 상수의 증가에 의한 효과와 입계에 유리질이 생겨 자벽이 쉽게 이동하지 못하는 효과 때문인 것으로 판단되었다.

• 한국정밀공학회지
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• 제18권2호
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• pp.177-185
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• 2001

This study shows the process design and forming analysis of permalloy shielding can that support the automobile multi-display parts to indicate the accurate information of car. This study is particularly important, since the strain and thickness of permalloy shielding can is known to affect the magnetic properties such as coercivity and permeability quite thickness of permalloy shielding can is known to affect the magnetic properties such as coercivity and permeability quite sensitively. The objective functions are strain and thickness deviation. The punch radius, die radius and blank holding force are considered as design parameters. Orthogonal array (OA) table and characteristics are applied to neural network (NN) as train data. After training, the optimal and robust condition of design parameters is selected. This study shows the correlation between the design methodology of NN and the statistical design of experiments (DOE) approach.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.715-719
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• 2009

In this study, a method to predict the consolidation behavior of soft clays and marine clays was developed by combining the equation of Terzaghi's 1-dimensional consolidation and CPTu dissipation. The special attention was given to the consolidation anisotropy due to the difference between 1-D consolidation and radial consolidation of CPTu dissipation. The analysis combining two equations enables direct application of CPTu results. And above all it doesn't require to sample undisturbed specimens and determine consolidation coefficient which is both costly and time consuming and often contains measuring error. It is also advantageous that CPTu test can be carried out any position and any depth. Clays typically have a greater horizontal permeability, $k_h$, than vertical permeability, $k_v$, and the coefficient of consolidation in the horizontal direction is generally higher than the vertical direction. Various data of horizontal and vertical consolidation coefficient ratio were collected and analyzed to develop and verify the method.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.60-61
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• 2003

Theoretical considerations on a giant magneto-impedance (GMI) effect in amorphous ribbons (i.e., thin films) have been made in terms of the expressions of effective permeability and impedance derived in the frame of classical electrodynamics and ferromagnetism. The dependence of GMI effect on the external do magnetic field (H$\_$ext/) and the frequency of alternating current are simulated and discussed in the knowledge of energy conversion consisting of the current energy loss, the ferromagnetic energy consumption, and the magnetic energy storage in the film. The obtained results are summarized as follow: (a) As frequency f< 20 ㎒, the real part of effective permeability (${\mu}$′) changes slightly. The peak of the ${\mu}$′curve always locates at H$\_$ext/=H$\_$ani/ - the anisotropy field. However, the peak value of ${\mu}$′ tends to increase with increasing frequency in the frequency range of 11-20 ㎒. (b) In the frequency range, f= 21-23 ㎒, a negative peak additionally appears. Meanwhile, both the positive and negative peak values rapidly increase with increasing frequency and their peak positions shift towards a high H$\_$ext/. (c) The positive peak value of ${\mu}$′ starts to decrease at f= 29 ㎒ and its negative peak does so at about 35 ㎒. Then, both peaks keep such a tendency and their peak positions move to high H$\_$ext/, as increasing frequency. (d) The dependence of the imaginary part of effective permeability (${\mu}$") on the external dc magnetic field and the frequency of the alternating field indicates that there is only one peak involved in ${\mu}$" for the whole frequency range. (e) The impedance vs. magnetic field curves at various frequencies show that there is a critical value of frequency around f= 18-19 ㎒ where the transition between two frequency regimes occurs; the one (low frequency) in which ${\mu}$′ predominantly contributes to the GMI effect and the other (high frequency) in which ${\mu}$" determines the GMI effect.

• 한국재료학회지
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• 제12권6호
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• pp.442-446
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• 2002

Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• 한국세라믹학회지
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• 제43권3호
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• pp.143-147
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• 2006

Co-Fe-Al-O nanogranular thin films were fabricated by RF-magnetron sputtering under an $Ar+O_2$ atmosphere. High resolution transmission electron microscopy revealed that the Co-Fe-Al-O films are composed of bcc (Co, Fe) nanograins finer than 5 nm and an Al-O amorphous phase. A very large electrical resistivity of $374{\mu}{\Omega}cm$ was obtained, together with a large uniaxial anisotropy field of 50 Oe, a hard axis coercivity of 1.25 Oe, and a saturation magnetization of 12.9 kG. The actual part of the relative permeability was measured to be 260 at low frequencies and this value was maintained up to 1.3 GHz. The ferromagnetic resonance frequency was 2.24 GHz. The resulting Co-Fe-Al-O nanogranular thin films with a high electrical resistivity and high resonance frequency are considered to be suitable for GHz magnetic device applications.

• 전자공학회논문지A
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• 제31A권6호
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• pp.143-148
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• 1994

In order to study the effect of D.C resistivity of sample on electromagnetic loss of ferrite at microwave frequency, samples were prepared for having differences in resistivity of an order of two. Microwave permeability($\mu$), permitivity($\varepsilon$) and effective linewidth(${\Delta}H_{eff}$), and ferromagnetic resonance linewidth(${\Delta}$H) were characterized. Tan${\delta}{\mu}$, tan${\delta}{\varepsilon}$ and ${\Delta}H_{eff}$ were decreased with increasing the resistivity and (${\Delta}$H) was increased with increasing Fe concentration, which was due to an increase of anisotropy magnetic field (=Ha).

• 지질공학
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• 제21권4호
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• pp.349-359
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• 2011

점성토의 압밀거동은 투수성과 변형성에 영향을 받으며 그 중 투수성은 흙의 종류 및 상태, 특히, 이방성에 영향을 받는다. 연약지반의 투수계수는 피에조 콘 소산시험 및 실내압밀시험 (Oedometer test)에 의해 구할 수 있으며, 피에조 콘 시험으로 과잉간극수압 소산측정이 가능하여 수평압밀계수와 수평투수계수 평가에 유용하게 사용된다. 본 연구에서는 국내 서해안 및 남해안 지역의 해성 점성토층을 대상으로 피에조 콘 소산시험을 실시하였으며, 불교란 시료에 대한 실내시험(Oedometer, Rowe cell)을 실시하고 각 이론해 별로 비교 분석을 실시하였다. 연구결과 Jamiolkowski(M적용) 등(1985)의 해로 추정한 kh/kv가 이 연구 대상지반의 투수특성과 가장 유사하게 나타나 국내의 연약지반에서 피에조 콘 소산시험 및 실내시험 (Oedometer test)에 의하여 투수특성(kh/kv, kh)을 평가하는 방법으로서 이들 이론해의 적용을 추천한다.

• 한국자기학회지
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• 제25권1호
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• pp.10-15
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• 2015

높은 전기전도도를 가진 비자성 금속 코어와 연자성 쉘을 가진 복합와이어의 자기임피던스를 원주방향 투자율로 표현하는 모델을 맥스웰 방정식으로부터 유도하였다. Cu(직경 $100{\mu}m$)/$Ni_{80}Fe_{20}$(두께 $15{\mu}m$) 코어/쉘 복합 와이어를 전기도금방법으로 제작하였다. 코어/쉘 복합 와이어의 길이방향으로 10 kHz에서 10 MHz 범위의 주파수를 가지는 교류전류와 0 Oe에서 200 Oe 범위의 직류 자기장을 가하여 임피던스 스펙트럼의 자기장 의존성을 측정하였다. 유도된 모델을 적용하여 측정된 임피던스 스펙트럼으로부터 원주방향 복소 투자율 스펙트럼을 뽑아내었다. 뽑아낸 원주방향 복소 투자율 스펙트럼은 단일 완화주파수의 Debye 식으로 매우 잘 곡선적합되는 완화형 분산을 보였다. 원주방향 복소 투자율 스펙트럼의 자기장 의존성을 분석하여, 본 코어/쉘 복합 와이어의 경우 길이 방향의 자기이방성을 가지며 원주방향으로의 자화회전이 완화형 복소 투자율 스펙트럼에 기여하는 단일 성분이라는 것을 규명하였다.

• 지질공학
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• 제26권4호
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• pp.593-600
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• 2016

본 연구에서는 국내의 107개 터널 설계 과정에서 수행한 현장 및 실내시험 자료 4,280개를 이용하여 암반 및 무결암의 역학적 특성을 암종 및 강도별로 분석하였다. 분석된 물리 및 역학적 특성은 단위중량, 점착력, 내부마찰각, 변형계수, 탄성계수, 포아송비, 일축압축강도, 인장강도, 투수계수, 비중이다. 평균값의 분석 결과에 의하면 편마암은 비중, 화강암은 투수계수, 퇴적암은 단위중량과 점착력, 내부마찰각, 화산암은 변형계수와 탄성계수, 일축압축강도, 인장강도, 변성암은 포아송비에서 가장 높은 값을 보인다. 역학적 특성의 분포 범위는 암종 및 강도를 고려한 분석에도 불구하고 넓게 분포하며, 이는 암반의 불균질성과 이방성에 기인하는 것으로 판단된다.