• Journal of electromagnetic engineering and science
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• 제19권2호
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• pp.71-81
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• 2019

This paper presents a design methodology for wideband single-layered microwave absorbers with arbitrary absorption at the design center frequency using reactive Salisbury screens. The bandwidth of the absorber increases when the flatness of the reflection response at the design center frequency is maximized. Based on this observation, closed-form design formulas for wideband absorbers are derived. As they are scalable to any design frequency, wideband reactive screens can be systematically realized using two-dimensional periodic crossed-dipole structures patterned on a resistive sheet. Based on this method, a single-layered absorber with a 90% bandwidth improved to 124% of the design center frequency is presented. For the purpose of physical demonstration, an absorber with a design center frequency of 10 GHz is designed and fabricated using a silver nanowire resistive film with a surface resistance of 30 Ω/square. The measured absorption shows a good agreement with both the calculation and the electromagnetic simulation.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2003년도 춘계공동학술대회논문집
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• pp.97-101
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• 2003

우수한 휴대폰용 전파흡수체를 개발하기 위해 실리콘을 지지재로 한 Mn-Zn 페라이트를 개발하여 전파흡수능을 조사하였다. 본 연구에서는 시편의 제작온도가 전파흡수능에 미치는 영향을 연구하였으며 온도가 증가함에 따라 tan $\delta$ > 1을 나타내는 주파수가 저주파로 이동하는 경향을 나타내었고 이로 인해 70 $^{\circ}C$에서 제작한 1 mm 두께의 전파흡수체가 휴대전화의 중심사용 주파수인 1.8 GHz 부근에서 3.4 ㏈인 우수한 흡수능을 나타내었다.

• Journal of Radiation Protection and Research
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• 제42권1호
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• pp.21-25
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• 2017

Background: We are developing L-band and S-band microwave dielectric absorption systems aiming novel dosimetry using DNAs, such as plasmid DNA and genomic DNA, and microwave technology. Materials and Methods: Each system is composed of a cavity resonator, analog signal generator, circulator, power meter, and oscilloscope. Since the cavity resonator is sensitive to temperature change, we have made great efforts to prevent the fluctuation of temperature. We have developed software for controlling and measurement. Results and Discussion: By using this system, we can measure the resonance frequency, f, and ${\Delta}Q$ (Q is a dimensionless parameter that describes how under-damped an oscillator or resonator is, and characterizes a resonator's bandwidth relative to its center frequency) within about 3 minutes with high accuracy. Conclusion: This system will be expected to be applicable to DNAs evaluations and to novel dosimetric system.

• Current Applied Physics
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• 제18권11호
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• pp.1410-1414
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• 2018

Magnetic nanoparticles (MNP) have attracted considerable interest in many fields of research and applied science due to their impressive properties. In the past, especially biomedical problems have promoted the development of MNPs. For technical applications e.g. wastewater treatment and absorption of electromagnetic waves, the existing synthesis approaches are too expensive and/or the producible quantities are too low. In this work we present a method for simple preparation of size-controlled magnetic iron oxide nanoparticles by electroerosion dispersion (EED) of carbon steel in water. We describe the synthesis method, the laboratory installation and discuss the structural, chemical and electromagnetic properties of the synthetized EED powders as well as their applicability for microwave absorption compared to other available ferrite powders.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2007년도 동계학술연구발표회 및 스핀트로닉스와 나노물리에관한 국제심포지움
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• pp.216-216
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• 2007

• 한국환경과학회지
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• 제17권5호
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• pp.493-500
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• 2008

This paper describes the adsorption/desorpton efficiency of a modified activated carbon by irradiated microwave to treat toluene. By employing microwave energy, the regeneration time was considerably shortened compared with conventional thermal heating regeneration. New adsorbent called ACB (Activated Carbon-Bentonite) was prepared from powder activated carbon with mixing bentonite as a binder. Specific surface area, average pore size and total pore volume of ACB were calculated from the nitrogen adsorption/desorption isotherm. The surface of ACB was characterized with scanning electron microscope(SEM). The results showed that the specific surface area, total pore volume, average pore size of ABC was not influenced by regenerating cycle with microwave irradiation. Toluene was adsorbed onto ACB which desorbed by MW irradiation. Absorption capacity of ACB was 0.117 $g_{toluene}/g_{ACB}$. Desorption efficiency of toluene increased as higher microwave output was applied.

• 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.

• Composites Research
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• 제27권6호
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• pp.225-230
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• 2014

In this study, a novel microwave absorber which consists of a structural part, a resistive sheet, and a low dielectric layer is proposed. Unlike the conventional Salisbury screen, a newly proposed absorber is capable of a range of absorbing performance, from narrowband to broadband. In the case of the narrowband absorber, the fabricated absorber with optimized design parameters has a strong resonance at 9.25 GHz and reflection loss of -44 dB with satisfying the -10 dB absorption in whole X-band (8.2 GHz~12.4 GHz). For the broadband absorber design, the reflectivity was minimized in the considered frequency ranges. The designed absorber showed two weak resonances near 6.5 GHz and 16.5 GHz and satisfied the -10 dB absorption from C-band to Ku-band (4 GHz~18 GHz). The measured reflection loss of fabricated absorber was well matched with simulation results, though the measurement was only performed on X-band. For the Salisbury screen to be capable of broadband absorption, it should be stacked multiply in a structure known as the Jaumann absorber. However, for the microwave absorber presented here, broadband as well as narrowband capabilities can be implemented without a change of the structure.

• 한국식품저장유통학회지
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• 제13권3호
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• pp.344-350
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• 2006

혼합곡의 식미를 높이고 쌀과 함께 취반이 용이하게 하고자 찹쌀, 현미, 현미찹쌀, 찰보리, 서리태, 흑태, 팥 7가지 곡류와 두류를 대상으로 침지와 건조 전처리 조건을 검토하였다. 각 곡류와 두류의 수분흡수량은 서리태와 흑태가 가장 높게 나타났고, 보리, 찹쌀, 멥쌀, 현미찹쌀, 현미, 팥 순서를 보였다. 침지온도별 수분흡수량은 온도가 높을수록 수분흡수량이 증가하였고 수분흡수평형에 도달하는 시간이 단축되었다. 두류의 분쇄별 수분흡수량은 분쇄가 많이 될 수록 수분흡수량이 증가하였고 수분흡수평형에 도달하는 시간이 단축되었다. 침지한 시료를 실온, 열풍 $30^{\circ}C,\;50^{\circ}C$와 마이크로파 300 W, 700 W, 1000 W 출력으로 건조하였다. 그 결과 마이크로파 700 W 건조가 실온과 열풍, 마이크로파 300W에 비하여 시료의 손상없이 가장 단시간 내에 건조할 수 있었다. 따라서 혼합곡의 전처리 조건은 $30^{\circ}C$에서 1시간 침지한 후 마이크로파 700W에서 건조하는 것이 가장 적합한 것으로 사료되었다.

• 한국식품조리과학회지
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• 제14권1호
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• pp.44-49
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• 1998

Microwave oven을 이용한 취반 시 최적 취반조건을 설정하기 위하여 전자렌지의 출력 및 가열시간을 달리하여 취반한 밥의 관능적 특성을 조사하였다. 쌀 1cup(약 173 g)을 수세하여 290 ml 물을 넣고 1시간동안 침지시킨 후 전자렌지의 출력과 가열시간을 5단계로 조절하면서 취반하였다(1단계; 온도상승기, 2단계: 수분흡수기1, 3단계: 수분흡수기2, 4단계: 열 침투기, 5단계: 호화완료기). 예비실험에서 설정한 출력과 가열시간에 따른 실험조건 수는 1200treatments였으나 1차, 2차에 걸친 취반실험 결과로부터 32가지의 최적 취반조건을 선정하였다. 그 중에서 다시 다음 3가지를 전자렌지의 대표적 인 취반조건으로 제시할 수 있었다. 1) 출력(7) 5:00-출력(1) 5:00(2) 5:00-출력(2) 6:00-출력(7) 4:00 2) 출력(8) 4:25-출력(1) 5:00-출력(2) 5:00-출력(2)