• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 13th KACG Technical Meeting `97 Industrial Crystallization Symposium(ICS)-Doosan Resort, Chunchon, October 30-31, 1997
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• pp.155-159
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• 1997

We investigated the effect of mechanical backside damage in Czochralski silicon wafer. The intensity of mechanical damage were evaluated by minority carrier recombination lifetime by a laser excitation/microwave reflection photoconductance decay method, photo-acoustic displacement method, X-ray section topography, and wet oxidation/preferential etch methods. The data indicate that the higher the mechanical damage intensity, the lower the minority carrier lifetime, and the photoacoustic displacement values are also increased proportionally.

• 전자공학회논문지A
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• 제29A권11호
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• pp.14-18
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• 1992

A gradient matrix method in conjunction with the transmission-reflection method to determine the complex permittivity and permeability of a microwave material is presented. This method does not incur the phase ambiguity due to an improper sample length, and is applicable to the measurement of low-loss materials of a half wavelength. A gradient matrix for a coaxial cable sample is derived, and the results are illustrated.

• 한국항만학회지
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• 제5권2호
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• pp.77-84
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• 1991

This paper is compared with fourier series and least square polynomial fit and interpolation to mechanism stated number in electro-optical distance measuring instrument. Systematic instrumental errors occurring in electro-optical systems include uncertainties in the position of the electrical center of the transmitter, uncertainties in the effective center of the reflectors. frequency drift and instrument nonlinearity. Microwave systems are affected by uncertainties in the electrical centers of the master and remote units and by a phenomenon called group swing or reflection. As the result of this study, mechanism stated number will be used as verification of electro0optical measuring instrument to distance measurement.

• 자원리싸이클링
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• 제7권4호
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• pp.22-26
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• 1998

M-type Ba-ferrite(${BaFe}_{12-2X}{Ti}_{X}{Co}_{X}{O}_{19}$)의 ${Fe}^{3+}$ 이온 대신에 A이온의 위치에는 비자성 이온인 ${Ti}^{4+}$을, Me이온은 위치에는 ${Co}^{2+}$을 치환시켜 치환량 x의 변화에 따른 결정자기이방성 감소를 관찰하고, 고주파 대역에서 전파흡수재로서 사용가능 여부를 실험하였다. 치환결과 보자력은 결정자기이방성이 감소함에 따라 급격히 감소하는 경향을 보였으며, 포화자화값은 ${Fe}^{3+}$이온 대신에 비자성인 ${Ti}^{4+}$이온이 치환됨에 따라 거의 직선적으로 감소하였다. 특히, 치환량이 1.2일 때 보자력은 185 Oe로 가장 낮았고, 포화자화는 43.5emu/g의 값을 나타내었다. 반사손실을 계산한 결가 Ti-Co 치환량 0.8일 때 2mm흡수체의 경우 10~16㎓의 대역에서 반사손실-10㏈(90%흡수)이하였으며, 감쇠능의 측정결과 12~16㎓의 대역에서 20㏈(99% 감쇠)로 12~16㎓의 고주파 대역에서 전파흡수재로 사용이 가능함을 예측할 수 있었다.

• 폴리머
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• 제33권5호
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• pp.420-428
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• 2009

In this study, the composites containing carbon black (CB) or carbon fibers were prepared, and the microwave absorbing properties and the absorption mechanism of them were investigated and discussed in the frequency range of 2-18 GHz, respectively. The optimum mass fraction of CB has been found as 6%, and the carbon fibers were discovered to absorb radar wave either under parallel or vertical polarization, the suitable gap distance between each bundle of which was 5 mm. According to the results of the single constitute absorber samples, the structured composites with the two kinds of absorbers combination were fabricated and studied at 2-18 GHz. The top layer absorbers affect the absorption performance a lot; the maximum reflection loss of composites with CB as top layer absorbers was -31.8 dB with the frequency range of 2.4 GHz below -10 dB, and the other type with CFs as the top layer absorbers obtained the reflection loss peak value of -31.4 dB with 2 GHz below-10 dB.

• Composites Research
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• 제24권2호
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• pp.38-45
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• 2011

본 논문에서는 유리섬유 강화 복합재 적층판으로 이루어진 단일층 Dallenbach layer의 전파흡수체의 최적화 기법을 제시하고 그 성능을 분석하였다. 복합재 적층판의 전기적 특성을 제어하기 위해서 탄소나노튜브(CNT)를 혼합한 프리프레그를 사용하였다. 최적화 설계 기법은 유전자 알고리즘을 사용하였으며, 이를 이용하여 다양한 주파수에서 흡수체를 설계하고, 복합재의 두께 및 CNT 함유율을 최적화하였다. CNT 함유율의 최적화를 위해서는 복합재의 복소 유전율의 수치적 모델이 사용되었다. 전파흡수체의 최적설계에서 주파수에 따라서 CNT 함유율은 비례하여 증가하고, 흡수체의 두께는 반비례하여 감소한다. 흡수체의 -10 dB 흡수대역폭은 흡수체가 설계된 중심주파수에 비례하여 증가한다. 설계된 흡수체의 검증을 위해서 10 GHz에서 중심주파수를 갖는 흡수제를 제조하고 그 성능을 평가하였다. 복합재 적층판의 복소 유전율과 전파흡수체의 반사손실은 벡터회로망분석기와 7 mm 동축관을 이용하여 측정하였다. 복합재의 두께와 복소 유전율에 있어서의 측정된 값과 예측치의 차이에 의해서 중심주파수의 이동, 중심주파수에서의 반사손실의 감쇄, 흡수대역폭의 감소가 발생하였다.

• 한국ITS학회 논문지
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• 제9권2호
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• pp.41-50
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• 2010

본 논문에서는 다수의 이동통신 서비스를 위한 새로운 구조의 다중 대역 안테나를 설계 및 제작하였다. 제안된 안테나는 서로 다른 크기와 각도를 가지는 공동 접지된 두 개의 슬롯들에 의하여 다중 대역 안테나 특성을 가진다. 또한 안테나의 크기를 줄이고 이득을 향상시키기 위하여 삼면에 초크를 구성하였다. 안테나의 설계는 유한 적분법과 구조 근사법을 기본으로 하는 CST Microwave Studio 상용 프로그램을 사용하여 최적화한 후, 제작 및 측정을 하였다. 측정 결과 824 ~ 894 MHz와 1885 ~ 2500 MHz에서 반사계수가 -11 dB 이하(VSWR < 1.8)이며, 이득은 6 dBi 이상이었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.724-726
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• 1992

In this paper, the permeability ($\mu_{\tau}'$, $\mu_{\tau}''$), dielectric constants($\varepsilon_{\tau}'$, $\varepsilon_{\tau}''$) and absorbption characteristics of Ferrite/Rubber 0-3 composites were investigated. The composite specimens were prepared by molding and curing the mixtures of matrix rubber and Ni-Zn ferrite powders which were synthesized by wet-direct method. The permeability ($u_{\tau}'$) of specimen was decreased from 2.58 to 0.7 in the range of 1$\sim$7(GHz) and kept constant 0.7$\sim$0.8 at higher than 7(GHz), the higher the frequency was, the less the valves of $u_{\tau}"$ was from 1.57 to 0.03. The optimum thickness of microwave absorber, utilizing the Smith chart, was 5(mm). The reflection loss shows over than 20(dB) from 5.5(GHz) to 7.5(GHz) at 5(mm) thickness and relative band width(B/fm) was about 30%.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 춘계학술대회 논문집
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• pp.236-238
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• 1997

A cellular power amplifier using an APCVD(Atmospheric Pressure Chemical Vapor Deposition)-grown SiGe base HBT of ETRI has been designed with a linear simulation CAD. The Si/SiGe HBT with an emitter area of 2$\times$8${\mu}{\textrm}{m}$$^2$typically has a cutoff frequency(f$_{T}$) of 7.0 GHz and a maximum oscillation frequency(f$_{max}$) of 16.1 GHz with a pad de-embedding A packaged power Si/SiGe HBT with an emitter area of 2$\times$8$\times$80${\mu}{\textrm}{m}$$^2$typically shows a f$_{T}$ of 4.7 GHz and a f$_{max}$ of 7.1 GHz at a collector current (Ic) of 115 mA. The power amplifier exhibits a Forward transmission coefficient(S21) of 13.5 dB, an input and an output reflection coefficients of -42 dB and -45 dB respectively. Up to now the III-V compound semiconductor devices hale dominated microwave applications, however a rapid progress in Si-based technology make the advent of the Si/SiGe HBT which is promising in low to even higher microwave range because of lower cost and relatively higher reproducibility of a Si-based process.ess.ess.

• Journal of electromagnetic engineering and science
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• 제17권4호
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• pp.169-177
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• 2017

The role of electromagnetic (EM) waves in magnetic fusion plasma-ranging from radio frequency (RF) to microwaves-has been extremely important, and understanding of EM wave propagation and related technology in this field has significantly advanced magnetic fusion plasma research. Auxiliary heating and current drive systems, aided by various forms of high-power RF and microwave sources, have contributed to achieving the required steady-state operation of plasmas with high temperatures (i.e., up to approximately 10 keV; 1 eV=10000 K) that are suitable for future fusion reactors. Here, various resonance values and cut-off characteristics of wave propagation in plasmas with a nonuniform magnetic field are used to optimize the efficiency of heating and current drive systems. In diagnostic applications, passive emissions and active sources in this frequency range are used to measure plasma parameters and dynamics; in particular, measurements of electron cyclotron emissions (ECEs) provide profile information regarding electron temperature. Recent developments in state-of-the-art 2D microwave imaging systems that measure fluctuations in electron temperature and density are largely based on ECE. The scattering process, phase delays, reflection/diffraction, and the polarization of actively launched EM waves provide us with the physics of magnetohydrodynamic instabilities and transport physics.