• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.673-676
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• 2003

This paper describes the modeling and experimental results for Bulk Acoustic Wave(BAW) Resonator using PolyVinyliDene Fluoride(PVDF). We measured the input reflection coefficient ($S_{11}$) of resonators using vector network analyzer and experimental results were measured fundamental resonance at 2.3 GHz with a return loss of -29 dB. Because of fabricated resonator without etching process, we can confirm a possibility of resonator application as using a PVDF.

• Journal of the Optical Society of Korea
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• 제11권1호
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• pp.1-5
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• 2007

We investigate the efficiency of an optical intensity modulator based on an electrically tunable $LiNbO_3$ reflection grating. Assuming a grating coupling coefficient and the waveguide propagation loss, waveguide length is varied to find its effect on the modulator slope efficiency and the device capacitance. With the low propagation loss of the $LiNbO_3$ waveguide, a very efficient optical intensity modulator can be achieved for a low frequency (${\sim}1GHz$) as long as the requirement for the grating coupling coefficient is satisfied.

• 한국광학회지
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• 제13권5호
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• pp.408-413
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• 2002

We demonstrated a polarization dependent type 2$\times$2 optical switch, using a binary reflection type SLM. Reflection type FLC was used as a half wave retardation plate. Two inputs were controlled by each SLM for the desired output direction. In conclusion, in the "1" state the average optical loss was 6.6 ㏈, and in the "0" state the average optical loss was 14.6 ㏈, and measured the switching speed as 75 $mutextrm{s}$. By using this method, a polarization dependent type 2$\times$2 optical switch can be demonstrated and the possibility of a 4-port WDM optical switch also verified.

• Journal of information and communication convergence engineering
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• 제21권3호
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• pp.192-197
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• 2023

A Distributed reflection denial of service (DRDoS) is a variant of DDoS attacks that threatens the availability of services to legitimate users. In response to this evolving threat landscape, the cybersecurity industry and service providers have intensified their efforts to develop effective countermeasures. Despite these efforts, attackers continue to innovate, developing new strategies and tools while becoming more sophisticated. Consequently, DRDoS attacks continue to be harmful. Therefore, ongoing research and development is essential to improve defense against DRDoS attacks. To advance our understanding and analysis of DRDoS attacks, this study examines the unique characteristics of DRDoS attacks and quantifies the risks involved. Additionally, it adopts a quantitative rather than traditional qualitative methods to derive and apply risk, particularly the probability of loss that can be caused by DRDoS attacks.

• Journal of the Optical Society of Korea
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• 제20권5호
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• pp.614-622
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• 2016

In this paper, we propose a novel differential equation method for designing a total internal reflection (TIR) LED lens with double freeform surfaces. A complete set of simultaneous differential equations for the method is derived from the condition for minimizing the Fresnel loss, illumination models, Snell’s Law of ray propagation, and a new constraint on the incident angle of a ray on the light-exiting surface of the lens. The last constraint is essential to complete the set of simultaneous differential equations. By adopting the TIR structure and applying the condition for minimizing the Fresnel loss, it is expected that the proposed TIR LED lens can have a high luminous flux efficiency, even though its beam-spread angle is narrow. To validate the proposed method, three TIR LED lenses with beam-spread angles of less than 22.6° have been designed, and their performances evaluated by ray tracing. Their luminous flux efficiencies could be obviously increased by at least 35% and 5%, compared to conventional LED lenses with a single freeform surface and with double freeform surfaces, respectively.

• 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.

• 한국자기학회지
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• 제18권3호
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• pp.115-119
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• 2008

Permalloy를 30시간 볼밀 한 후 주사전자현미경으로 형상 및 입경을 분석하였으며, 볼밀 가공한 Permalloy의 입자들이 편편한 상을 가짐을 확인하였다. Permalloy를 실리콘 고무와 혼합하여 박형 전파흡수체를 제조하고 Network Analyzer을 이용하여 permalloy-고무 전파흡수체의 재료정수 및 전파흡수특성을 측정하였으며, 그들의 상관 관계를 비교 조사하였다. 가공한 permalloy-고무 복합재료는 높은 복소유전율 및 복소투자율을 가지며 미가공한 permalloy-고무 복합재료 보다 전파흡수 특성이 우수하였다. 또한 전파흡수체 두께에 따라서 정합주파수가 낮은 주파수 대역으로 shift 됨을 알 수 있고, 1.3 mm의 두께로 제조한 전파흡수체에서는 이동통신주파수 대역인 $1.65\;GHz{\sim}1.86\;GHz$에서 가장 우수한 전파흡수특성을 나타내었다.

• 한국자기학회지
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• 제27권2호
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• pp.49-53
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• 2017

THz 대역 전파흡수체를 구현하기 위해 split cut wire(SCW)와 배면 도체로 구성되는 단위 셀 구조를 제안하였다. 배면이 금속으로 단락된 유전체 기판 상에 SCW가 배열된 메타소재에서 SCW의 길이와 폭을 조절하여 THz 대역에서 완전 전파흡수체(5.5~6.0 THz에서 반사손실 -20 dB 이하)의 구현이 가능하였고, 인덕턴스-커패시턴스 (L-C) 공진기 회로이론으로 이를 설명하였다. 길이가 서로 다른 두 개의 SCW를 하나의 단위 셀 안에 같이 배치함으로써 두 개의 흡수 피크를 얻을 수 있었다. SCW 간의 간격이 넓어짐에 따라 두 번째 공진주파수는 거의 변화가 없지만 첫 번째 공진주파수는 저주파로 이동하면서 반사손실 값이 현저히 감소하는 경향이 나타났다.

• 자원리싸이클링
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• 제9권6호
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• pp.31-35
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• 2000

Mn-Zn ferrite 폐기물을 시멘트와 혼합한 복합전파흡수체를 제작하여 재료정수 및 반사감쇠량을 조사하였다. 지지재로 사용한 시멘트는 실리콘 고무의 재료정수와 비교하여 높은 복소유전율($\varepsilon$=$_{r}$': 7.6, $\varepsilon_{r}$ ": 0.6)을 나타내었고, Mn-Zn ferrite 폐기물과 시멘트의 혼합무게비(F/C)가 증가함에 따라 복소유전율은 감소하였고, 복소투자율은 증가하였다. 최대반사감쇠량을 나타내는 주파수는 F/C가 1에서 3으로 증가함에 따라 2.7 GHz에서1.3 GHz로 감소하였고, 정합두께는 8.7 mm에서 12.7 mm로 증가하는 경향이 나타났다. 모든 시편에서 최대반사감쇠량은 -40 dB 이상으로 Mn-Zn ferrite 폐기물을 전파흡수체로 활용이 가능하다.

• 전기학회논문지
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• 제62권1호
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• pp.76-82
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• 2013

The solar cell is a device to convert light energy into electric, which supplies power to the external load when exposed to the incident light. The photocurrent and voltage occurred in the device are significant factors to decide the output power of solar cells. The crystalline silicon solar cell module has photocurrent loss due to light reflections on the glass and EVA(Ethylene Vinyl Acetate). These photocurrent loss would be a hinderance for high-efficiency solar cell module. In this paper, the quantitative analysis for the photocurrent losses in the 300-1200 wavelength region was performed. The simulation method with MATLAB was used to analyze the reflection on a front glass and EVA layer. To investigate the intensity of light that reached solar cells in PV(Photovoltaic) module, the reflectance and transmittance of PV modules was calculated using the Fresnel equations. The simulated photocurrent in each wavelength was compared with the output of real solar cells and the manufactured PV module to evaluate the reliability of simulation. As a result of the simulation, We proved that the optical loss largely occurred in wavelengths between 300 and 400 nm.