• 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.

• 한국염색가공학회지
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• 제10권4호
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• pp.7-14
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• 1998

Microwaves are high frequency radiation capable of generating very rapid, uniform and efficient heating of textile material. Microwave heated dyeing of polyester fabric was tried with different solvent systems, irradiation time and dye concentration. Microwave fixation methods were used with 100% water,30% urea, EG and DMF, respectively, pad-baths in which the padded fabrics were exposed over a heated or boiling water bath to maintain sufficient moisture content during irradiation. In order to ascertain the relation between the dyeing property of polyester fabric and the microwave irradiation condition caused by microwave heating, the K/S values and fastness properties of dyed fabrics such as light, washing and sublimation fastness were measured.

• 한국전자통신학회논문지
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• 제4권2호
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• pp.75-81
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• 2009

본 논문에서는 10.525GHz에서 동작하는 마이크로파 도플러 레이더 센서를 설계/제작하였다. 움직이는 물체를 이용한 측정을 통해 도플러 효과에 따른 센서의 특성을 연구 분석하였으며, 측정 결과를 통해 물체의 속도와 물체와 센서 사이의 거리에 따라 특성에 주파수의 차이를 보임을 알 수 있었다. 측정된 결과를 이용해 마이크로파 도플러 레이더 센서의 FMCW 신호에 의하여 댁내 보안탐지와 같은 용도로 활용할 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기물성,응용부문
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• pp.109-111
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• 2002

The fundamental principles of the operation of microwave discharges that are used to convert microwave energy to broad spectrum visual light are known. In this paper, emission dependance of microwave discharges in mixture content of sulfur with noble gases was studied. It is shown that the excitation of this gaseous mixture is carried out in two phases; (1) ionization of noble gas atoms by a microwave field and (2) the consequent maintenance of slightly ionized nonequilibrium plasma by the field. These two processes have essentially various thresholds for the microwave pump. The purpose of this work is to investigate spectral properties of the high frequency discharges in a mixture sulfur vapors with noble gases.

• Computers and Concrete
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• 제8권4호
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• pp.425-443
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• 2011

Most previous studies have generally overlooked the contribution of thermal stresses generated within the concrete mass when subjected to microwave heating and reported on pore-pressure as being the dominant cause of surface spalling. Also, the variation in electromagnetic properties of concrete and its effects on the microwave heating process have not been studied in detail. In this paper, finite element modeling is used to examine the simultaneous development of compressive thermal stresses and pore-pressure arising from the microwave heating of concrete. A modified Lambert's Law formulation is proposed to estimate the microwave power dissipation in the concrete mass. Moreover, the effects of frequency and concrete water content on the concrete heating rate and pattern are investigated. Results show high compressive stresses being generated especially in concrete with a high water content when heated by microwaves of higher frequencies. The results also reveal that the water content of concrete plays a crucial role in the microwave heating process.

• Asian-Australasian Journal of Animal Sciences
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• 제18권1호
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• pp.27-31
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• 2005

Wheat straw was treated with microwave for 4 min and 8 min at a power of 750 W and frequency of 2,450 MHz. Chemical compositions of untreated, 4 min treated and 8 min treated straws were analyzed and in sacco degradabilities of all these straws in yak rumens were measured. Microwave treatment didn't significantly (p>0.05) affect the chemical composition of the straw. In sacco dry matter (DM) degradability of the straw after 18 h incubation in rumen was significantly (p<0.01) improved by microwave treatment. In sacco crude protein (CP) degradability of the straw was not (p>0.05) affected by microwave treatment. In sacco organic matter (OM) degradability of the straw was increased (p<0.01) by around 20% for both the 4 min and 8 min microwave treatment, that of acid detergent fibre (ADF) was increased (p<0.01) by 61.6% and 62.8%, and that of ash free ADF was enhanced by 72.1% and 69.6% for the 4 min and 8 min microwave treatment respectively. No significant difference was observed between the 4 min and 8 min microwave treatment on the degradability of DM, OM, CP, ADF and ash-free ADF of the straw.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.434-437
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• 2003

In this paper, we have developed a frequency mixer for the microwave phase conjugator. The circuit topology is the gate mixer using a pseudomorphic HEMT device. The operating frequencies are 4.0 GHz 2.01 GHz, and 1.99 GHz for LO, RF, and IF, respectively. Conversion gain is measured to be 12 dB and 1 dB compression point -34 dBm at the LO power of -4 dBm.

• 전기의세계
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• 제28권1호
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• pp.53-58
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• 1979

In the microwave heating system, a ferroresonant transformer is used to regulate the magnetron power fluctuation. For the simplification, nonlinear characteristics of the transformer and the magnetron are idealized to be piecewise linear. Dipped peak shape of the magnetron current is explained qualitatively by considering the fundamental and third harmonic frequency components in the circuit. Design equations providing the values of the leakage inductance, turn ratio of the transformer and the capacitance are derived analytically by cosnidering the fundamental frequency component only. The ferroresonant transformer is designed to obtain a required regulation and high input power factor from the derived design equations, and analytical calculations are compared with experimental measurements.

• 한국정보통신학회논문지
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• 제6권2호
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• pp.151-158
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• 2002

본 논문에서는 저 위상잡음과 고안정 특성을 나타내는 디지털 MMDS용 위상고정 발진기를 설계하였으며 전압제어 발진기용 능동소자의 비선형 등가모델에 의하여 저 위상잡음 파라미터와 안정된 전압제어 발진기의 필요충분 조건을 분석하였다. 설계된 전압제어 발진기에 위상고정루프를 적용하여 위상고정 마이크로파 발진기를 구현하였으며 고안정 전압제어 발진기에 대하여 시뮬레이션한 결과 －90dBc/Hz @ 10KHz의 위상잡음을 보였으며 위상고정 마이크로파 발진기에 대한 실험 결과 －85dBc/Hz @ 10KHz의 위상잡음을 얻었다. 고안정도와 저 위상잡음특성을 나타내는 위상고정 마이크로파 발진기의 설계모델을 디지털 MMDS 단말기용 고안정 주파수 합성기로 응용할 수 있음을 보였다.

• 전기전자학회논문지
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• 제22권3호
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• pp.780-785
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• 2018

본 논문에서는 tunable RF 기기에 적용이 가능한 $HfO_2$ 강유전체를 활용하여 metal-ferroelectric-metal (MFM) 커패시터를 구현하였으며 마이크로파 대역주파수 까지 전압에 따른 커패시턴스 tunability 특성을 고찰 하였다. 1kHz부터 5GHz 대역에 이르기까지 광범위한 범위의 커패시턴스-전압 특성을 분석하였으며 커패시턴스 tunability는 500 MHz 이상의 주파수에서 2.5 GHz 대역까지 ~3 %의 tunability가 유지되는 것을 확인 하여 마이크로파 주파수 대역에서 ALD $HfO_2$기반 전자 제어 가변 커패시터의 사용 가능성을 입증하였다.