• 한국결정성장학회지
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• 제33권6호
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• pp.294-302
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• 2023

Ni-Mn-Zn ferrite, Ni_0.5-xMn_xZn_0.5Fe₂O₄(0 ≤ x ≤ 0.5)를 sol-gel 법으로 합성하여 Mn 치환량 x에 따른 결정 구조와 미세구조, 자기적 특성, 고주파 특성, 그리고 전자기파 흡수 특성을 연구하였다. Mn의 함량이 증가함에 따라 보자력 (H_C)에 큰 변화 없이 포화자화값(M_S)이 연속적으로 감소하는 것을 확인하였다. Ni-Mn-Zn ferrite-epoxy(10 wt%) 복합체에 대하여 0.1~18 GHz 주파수 범위에서 고주파 복소 유전율(ε', ε'') 및 복소 투자율(µ', µ'') spectra를 측정하고 전송선 이론을 통하여 전자기파 흡수 특성을 평가하였다. 각 시료는 1.5~2.5 GHz 및 6~11 GHz 범위에서 최소 반사손실 RL_min < -40 dB를 만족하는 1, 2차 강한 전자기파 흡수 영역이 존재하였고, Mn이 치환됨에 따라 RL_min 주파수는 저주파 방향으로 이동하였다. 또한 Ni-Zn ferrite(x = 0) 시료에 대하여 자기장(H)을 100 Oe에서 최대 400 Oe까지 단계적으로 인가한 상태로 ε', ε'', µ', µ'' spectra를 얻고 전자기파 흡수 특성을 평가하였다. 인가자장의 증가에 따라 시료의 강자성 공명 주파수가 증가하기 때문에 µ', µ'' spectra도 고주파 방향으로 단계적으로 이동해갔으며 최대 전자기파 흡수 주파수도 이에 대응하여 이동하였다. 이는 Ni-Mn-Zn ferrite에서 전자기파의 흡수는 자기적 손실에 의존하기 때문이며 Mn의 치환이나 인가자장에 의해 µ', µ'' spectra를 조절하면 전자기파 흡수 주파수도 조절할 수 있음을 보여준다. Ni-Zn ferrite-epoxy는 2.8~11.6 GHz에서 RL < -10 dB를 만족하는 광대역 전자기파 흡수 특성을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 추계학술대회 논문집
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• pp.195-198
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• 1996

In conducting systems based on LB films, TCNQ derivatives have been extensively studied as electron acceptor molecules. We have investigated the optical, electrical, and magnetic properties of Viologen-(TCNQ￣)$_2$LB films. In UV/visible absorption measurements, we have observed TCNQ￣ peak at 380 nm and dimer peak at 620 nm. The electron spin resonance measurements infer that Viologen-(TCNQ￣)$_2$LB film exhibits anisotropic properly. In other words, the LB film shows angular dependence. Iodine doping affects the degree of charge transfer and the conductivity of the films. The UV/visible absorption spectra of the LB film doped with I$_2$show peaks at near 400~430 nm and there is no dimer absorption peak. The in-plane electrical conductivity of the undoped film is approximately 4.2$\times$10$^{-6}$ S/cm.

• Journal of Magnetics
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• 제19권2호
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• pp.155-160
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• 2014

The heating produced by the absorption of radiofrequency (RF) has been considered a secondary undesirable effect during MRI procedures. In this work, we have measured the power absorbed by distilled water, glycerol and egg-albumin during NMR and non-NMR experiments. The samples are dielectric and examples of different biological materials. The samples were irradiated using the same RF pulse sequence, whilst the magnetic field strength was the variable to be changed in the experiments. The measurements show a smooth increase of the thermal power as the magnetic field grows due to the magnetoresistive effect in the copper antenna, a coil around the probe, which is directly heating the sample. However, in the cases when the magnetic field was the adequate for the NMR to take place, some anomalies in the expected thermal powers were observed: the thermal power was higher in the cases of water and glycerol, and lower in the case of albumin. An ANOVA test demonstrated that the observed differences between the measured power and the expected power are significant.

• 전기학회논문지
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• 제64권3호
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• pp.429-432
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• 2015

Radio Frequency (RF) coils in Magnetic Resonance Imaging (MRI) systems interact with a patient's tissues, resulting in the absorption of RF energy by the tissues. The presence of an electrically conducting medical implant may concentrate the RF energy and causes tissue heating near the implant devices. Here we present a novel design for a medical lead to reduce this undesired heating. Specific Absorption Rate (SAR), an indicator of heating, was calculated. Remcom XFdtd software was used to calculate the peak SAR distribution (1g and 10 g) in a realistic model of the human body. The model contained a medical lead that was exposed to RF magnetic fields at 64 MHz (1.5 T MRI), 128 MHz (3 T MRI) and 300 MHz (7 T MRI) using a model of an MR birdcage body coil. Our results demonstrate that, our proposed design of adding nails to the medical lead can significantly reduce the SAR for different MRI systems.

• 전기전자학회논문지
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• 제22권2호
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• pp.446-454
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• 2018

In this work, we summarize the calculation processes of obtaining a scattering factor using with the equilibrium average projection scheme (EAPS), with moderately weak coupling (MWC) interaction, and obtain the line-shape formula of an electron-deformation phonon interacting system interested in the confinement of electrons by squarwell confinement potentials in quantum two dimensional system.. Through the numerical analysis, we analysis the magnetic dependence of absorption power, P(B) in several temperature and frequency difference dependence of absorption power $P({\Delta}{\omega})$, in several external field, where ${\Delta}{\omega}={\omega}-{\omega}_0$ and ${\omega}({\omega}_0)$ is the angular frequency (the cyclotron resonance frequency). The result of equilibrium average projection scheme (EAPS) in SER-MWC explains the properties of quantum transition quite well.

• 전기학회논문지
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• 제65권12호
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• pp.2019-2022
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• 2016

In the presence of an electrically conducting medical lead, radio frequency (RF) coils in magnetic resonance imaging (MRI) systems may concentrate the RF energy and cause tissue heating near the lead. A novel design for a medical lead to reduce this heating by introducing pins in the lead is presented. Peak 10 g specific absorption rate (SAR) in heart tissue, an indicator of heating, was calculated and compared for both conventional (Medtronic) lead design and our proposed design. Remcom XFdtd software was used to calculate the peak SAR distribution in a realistic model of the human body. The model contained a medical lead that was exposed to RF magnetic fields at 64 MHz (1.5 T), 128 MHz (3 T) and 300 MHz (7 T) using a model of an MR birdcage body coil. The proposed design of adding pins to the medical lead can significantly reduce the heating from different MRI systems.

• 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.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2015년도 임시총회 및 하계학술연구발표회
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• pp.139-139
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• 2015

• 동력기계공학회지
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• 제17권5호
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• pp.38-43
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• 2013

In order to design a wave energy generating system, a 6-DOF analysis technique is applied to CFD analysis on of a floating body and the behavior is interpreted according to the nature of the incoming waves. A spring constant is adopted to control the motion of multi floating bodies and to calculate the total average power absorption. Three cases of different wavelengths namely 20D, 30D and 40D have been modeled to analyze the total average power absorption. The average power absorption not only varies with the position of the floating body but also varies with wavelength. From the results obtained, it is concluded that the maximum total average power absorption is 9W approximately in wavelength 30D and the minimum total average power absorption is 4.3W approximately in wavelength 40D.

• Current Applied Physics
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• 제18권12호
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• pp.1465-1472
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• 2018

The magnetic and optical properties of Ce-doped ZnO systems have been widely demonstrated, but the effects of different strains of Ce-doped ZnO systems remain unclear. To solve these problems, this study identified the effects of biaxial strain on the electronic structure, absorption spectrum, and magnetic properties of Ce-doped ZnO systems by using a generalized gradient approximation + U (GGA + U) method with plane wave pseudopotential. Under unstrained conditions, the formation energy decreased, the system became stable, and the doping process became easy with the increase in the distances between two Ce atoms. The band gap of the systems with different strains became narrower than that of undoped ZnO without strain, and the absorption spectra showed a red shift. The band gap narrowed, and the red shift became weak with the increase of compressive strain. By contrast, the band gap widened, and the red shift became significant with the increase of tensile strain. The red shift was significant when the tensile strain was 3%. The systems with -1%, 0%, and 1% strains were ferromagnetic. For the first time, the magnetic moment of the system with -1% strain was found to be the largest, and the system showed the greatest beneficial value for diluted magnetic semiconductors. The systems with -3%, -2%, 2%, and 3% strains were non-magnetic, and they had no value for diluted magnetic semiconductors. The ferromagnetism of the system with -1% strain was mainly caused by the hybrid coupling of Ce-4f, Ce-5d, and O-2p orbits. This finding was consistent with Zener's Ruderman-Kittel-Kasuya-Yosida theory. The results can serve as a reference for the design and preparation of new diluted magnetic semiconductors and optical functional materials.