• 한국자기학회지
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• 제18권3호
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• pp.120-125
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• 2008

여러 가지 다른 조성의 NiCoZn ferrite를 공침법으로 제조한 후 소결온도를 변화시켜 NiCoZn ferrite 미분말을 제조하였다. 제조된 미분말의 미세조직, 결정구조 및 전기적 특성을 분석하였고, 복합형 NiCoZn ferrite 전파흡수체를 제작하여 전파흡수 특성을 분석하였다. 합성한 미분말들은 전형적인 NiCoZn spinel 구조를 지니고 있음을 확인하였고, 입자 크기가 평균 40 nm의 나노분말을 가짐을 알 수 있었다. NiCoZn ferrite를 소결온도를 달리하여 제조한 결과, $1250^{\circ}C$에서 소결된 NiCoZn ferrite가 불순물이 적고 초투자율 및 Q 값이 가장 낮게 나왔다. 또한 S-parameter를 측정하여 반사 감쇠율을 계산한 결과 두께 2 mm인 $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ 조성의 시트형 전파흡수체는 6 GHz의 주파수 대역에서 -3.1 dB의 반사 감쇠율을 보여주었다. 이런 측정 결과 6 GHz 이상의 고주파 영역에서 복합 ferrite 전파흡수체로서 응용이 가능할 것으로 사료된다.

• 한국전자파학회논문지
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• 제20권8호
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• pp.694-700
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• 2009

본 논문에서는 주변 유전체에 의한 성능 열화가 적고 잉크 프린팅 기법에 적합한 RFID 태그 안테나를 제안하였다. 제안된 태그 안테나는 PET 기판 위에 잉크 프린팅 기법으로 제작되어 대량 생산에 용이하며, 범용 RFID 사용 주파수($860{\sim}960$ MHz)를 만족시키고 주변 유전물질의 영향에 의한 성능 변화를 최소화 할 수 있도록 설계하였다. 제안된 태그 안테나는 본체 중앙부에 T 정합회로를 사용하고 미앤더 구조와 직선 구조의 보조 선로 2개를 본체 상단에 삽입하여 캐패시티브 결합을 이용해 태그 칩과의 임피던스 공액 정합이 쉽게 이루어지도록 하였다. 또한, 2개의 보조 선로가 각각 다른 부착 물체의 유전율에서 상호 보완적으로 전류를 유기시키도록 하여 주변 유전물질의 영향에 의한 성능 변화가 최소화 되도록 설계하였다. 측정 결과, 제안된 안테나는 $844{\sim}1,268$ MHz의 대역폭에서 반전력 반사 손실을 만족하였으며, 송신 출력이 20 dBm이고, 안테나 이득이 6 dBi인 리더 안테나를 사용하였을 때 자유공간에서 3.5 m의 인식 거리 성능을 보였다. 또한,나무(${\varepsilon}_r$=2.2)와FR4(${\varepsilon}_r$=4.3)같은 유전율을 가지는 물질에 부착 후 인식 거리를 측정한 결과 각각 2.61 m와 2.51 m의 인식 거리 성능을 보였다.

• 한국전자파학회논문지
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• 제26권1호
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• pp.101-112
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• 2015

II~VI족 화합물 반도체 $Zn_xCd_{1-x}S$ 박막을 Indium-tin-oxide(ITO)가 도포된 유리기판 상에 열증발법을 사용하여 증착하였다. 박막의 합성비(molar ratio) x($0{\leq}x{\leq}1$)는 CdS(x=0) 박막과 ZnS(x=1) 박막을 포함하여, 삼원화합물 $Zn_xCd_{1-x}S$ 박막을 제조하기 위하여 변화시켰다. 또한, 증착한 박막의 결정성을 높이기 위하여 진공전기로에서 열처리 하였으며, 분광학적 특성조사를 위해서는 $400^{\circ}C$에서 열처리한 $Zn_xCd_{1-x}S$ 박막이 최적임을 알았다. $Zn_xCd_{1-x}S$ 박막의 합성비(x)와 전자적 구조를 조사하기 위하여 X-선 광전자 분광법(XPS)을 사용하였고, 박막시료의 광학적 에너지 띠 간격 $E_g$는 자외선-가시광-근접 적외선(UV-Vis-NIR) 분광법으로 측정하였으며, 합성비(x)값이 0에서 1까지 변화함에 따라 2.44~3.98 eV 범위의 값을 보여주었다. 끝으로, THz-TDS(Time Domain Spectroscopy) 시스템을 사용하고 $Zn_xCd_{1-x}S$ 박막의 THz파 특성을 측정하여 테라헤르츠(THz) 영역용 전자 및 광학 소자로서 응용가능성을 확인하였다.

• 한국전자파학회논문지
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• 제26권1호
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• pp.39-46
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• 2015

본 논문에서는 2.4 GHz에서 동작하는 $90^{\circ}$ 하이브리드 커플러 구조에 전도성 고분자 화합물을 적용한 가스 센서를 제안하였다. 가스 센서에서 전도성 고분자 화합물(Conducting Polymer: CP)는 특정 가스를 검출하는 검출 물질로 사용되며, 특정 가스와 반응할 때 대개 물질의 일함수(work function)와 전도도(conductivity) 및 임피던스가 변하게 된다. 이러한 물성변화 특성의 근거로 마이크로파 대역에서 $90^{\circ}$ 하이브리드 커플러 구조에 전도성 고분자를 적용하여 가변 감쇄기 및 가변 위상 천이기 형태의 센서를 제작하였다. 본 연구에서 제안한 센서는 전도성 고분자 화합물의 높은 전도도를 이용하여 기존 전송선로의 일부를 전도성 고분자 물질로 대체하였다. 실험은 온도 $28^{\circ}$와 상대습도 85 % 환경에서 진행되었으며, 센서에 100 ppm 농도의 에탄올 가스를 노출시켰다. 그 결과, $S_{21}$의 진폭 특성이 최대 0.13 dB 변하였고, ${\angle}S_{21}=360^{\circ}$를 만족하는 주파수가 2.875 MHz 이동한 것을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.498-498
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• 2013

Atmospheric Pressure Plasmas have pioneered a new field of plasma for biomedical application bridging plasma physics and biology. Biological and medical applications of plasmas have attracted considerable attention due to promising applications in medicine such as electro-surgery, dentistry, skin care and sterilization of heat-sensitive medical instruments [1]. Traditional approaches using electronic devices have limits in heating, high voltage shock, and high current shock for patients. It is a great demand for plasma medical industrial acceptance that the plasma generation device should be compact, inexpensive, and safe for patients. Microwave-excited micro-plasma has the highest feasibility compared with other types of plasma sources since it has the advantages of low power, low voltage, safety from high-voltage shock, electromagnetic compatibility, and long lifetime due to the low energy of striking ions [2]. Recent experiment [2] shows three-log reduction within 180-s treatment of S. mutans with a low-power palm-size microwave power module for biomedical application. Experiments using microwave plasma are discussed. This low-power palm-size microwave power module board includes a power amplifier (PA) chip, a phase locked loop (PLL) chip, and an impedance matching network. As it has been a success, more compact-size module is needed for the portability of microwave devices and for the various medical applications of microwave plasma source. For the plasma generator, a 1.35-GHz coaxial transmission line resonator (CTLR) [3] is used. The way of reducing the size and enhancing the performances of the module is examined.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 특별 심포지엄 논문집
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• pp.1-14
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• 2007

This paper briefly reviews the history of the Korean geophysics and analyze the current status of geophysical researches. And the future prospects of geophysics are discussed based on social demands for the science and technology in Korea. About thirty universities offer geophysics courses in their academic curricula. Although the number of Ph.D. graduates in geophysics had been small until the year of 1990, but is rapidly increasing. In recent years about $7{\sim}8$ Ph.D's are produced every year. The major geophysical methods used in Ph.D. theses are seismic, electrical and electromagnetic methods, and earthquake waves and research themes are computational geophysics, which involve data processing, modelling, inversion and tomography, geological structures, and paleomagnetic studies in the order of numbers. The Solid Earth Geophysics is generally distinguished in two categories such as "Global Geophysics" and "Exploration Geophysics". However, they are intimately connected, and overlap in many sectors, especially in large scale research projects. The global geophysics has a more academic and general scientific meaning, and several research groups in Korean universities are carrying out the earthquake seismology and paleomagnetic studies. On the other hand the exploration geophysics focuses on practical application of geophysical concepts, and the public research institutes conduct large projects for exploration of energy and mineral resources and to cope with environmental and natural disaster problems. The geophysical studies for local geology and regional crustal structure utilize various survey methods and usually cover both academic and exploration purposes. The computational geophysics constitutes the indispensable theoretical backgrounds for all geophysical sectors. Many young Korean geophysicists, who have strong background in mathematics and physics, devote to the computational geophysics and several groups have made the internationally highest level achievements. But, Korean geophysicists have to expand their research interests to include more global-scale, high-tech researches and collaborative works with various other science groups.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.525-525
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• 2013

Low temperature plasma diagnosis is one of the big issues in laboratory scale or processing industry. One of the most powerful techniques of plasma diagnostics is the use of the scattering of electromagnetic radiation from the plasma. Electron temperature and density are important parameters for understanding the information of plasmas in the plasma processing industry. Laser scattering experiments on plasma can provide a substantial amount of information about plasma parameters such as the electron density ne, the electron temperature Te, and the neutral density nn and temperature Tn. Thomson scattering spectroscopy is used several method, in accordance with detector type. Commonly, Thomson scattering is used several notch filter to separate expanded wavelength. Since using a spectrometer with surface relief grating or notch filter, the system of the measurement will be complicated and bigger. In this study, using VPHG (Volume Phase Holographic Grating) in order to install the simple and cheap system. VPHG has the advantage of the system installation, because it can be Transmission Type. The diffraction efficiency and dispersion angle of VPHG is higher than the surface relief grating relatively. For a wavelength and bandwidth selection, Using a slit or mask to select a rejection wavelength instead of notch filter.

• 천문학회보
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• 제41권1호
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• pp.45.1-45.1
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• 2016

Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. In magnetohydrodynamics, magnetic flux can be decreased by diffusion in O-lines. In kinetic physics, however, an asymmetry of the velocity distribution function can generate new magnetic flux near O- and X-lines, hence a dynamo effect. We have found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.

• 산업경영시스템학회지
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• 제22권53호
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• pp.69-78
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• 1999

We developed an apparatus for odorous stimuli control to record olfactory evoked potentials from human scalp. The characteristics of the apparatus were as follows. 1. Translating the subjects respiration into electric signals with a sensor attached to the nose. The period and timing of odorous stimuli could be adjusted, so that stimuli could be synchronous with respiration. 2. The respirations translated into electric signals were made constant in amplitude by using an auto gain control circuit. 3. The interstimulus interval of odorous could be arbitrarily selected once every 1 to 9 respirations so that adaptation could be prevented. We obtained olfactory - evoked potentials (OEPs) to odorous stimuli using this apparatus from the site of Cz, whose positive peak latencies were approximately $180{\pm}23ms$. Such response were not recorded if oxygen stimuli were used instead of odorous or with click sounds produced by the switching electromagnetic valve.

• Macromolecular Research
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• 제17권11호
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• pp.863-869
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• 2009

The effect of a multiwalled carbon nanotube (MWCNT) dispersion on the electrical, morphological and rheological properties of polycarbonate (PC)/MWCNT composites was investigated, with and without pretreating the MWCNTs with hydrogen peroxide oxidation and lyophilization. The resulting PC/treated MWCNT composites showed higher electrical conductivity than the PC/untreated MWCNT composites. The morphological behavior indicated the treated composites to have greater dispersion of MWCNTs in the PC matrix. In addition, the electromagnetic interference shielding efficiency (EMI SE) of the treated composites was higher than that of the untreated ones. Rheological studies of the composites showed that the complex viscosity of the treated composites was higher than the untreated ones due to increased dispersion of the MWCNTs in the PC matrix, which is consistent with the electrical conductivity, EMI SE and morphological studies of the treated composites. The latter results suggested that the increased electrical conductivity and EMI SE of the treated composites were mainly due to the increased dispersion of MWCNTs in the PC matrix.