• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1383-1389
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• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

• The Journal of the Acoustical Society of Korea
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• v.23 no.4
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• pp.296-302
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• 2004

Acoustic experiments are performed for a seafloor classification from 19 May to 25 May 2003. The six different sites of bottom composition are settled and the bottom reflection losses with frequencies (30, 50, 80. 100, 120 kHz) are measured. Sediment samples were collected using gravity core and the sample was extracted for grain size analysis. The fuzzy logic is used to classify the seabed. In the fuzzy logic. Bottom 1083 model of frequency dependence is used as the input membership functions and the output membership functions are composed of the Wentworth grain size of the bottom. The possibility of the seafloor classification is verified comparing the inversed mean grain size using fuzzy logic with the results of the coring.

• Composites Research
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• v.15 no.2
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• pp.18-23
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• 2002

The absorption and the interference shielding of the problems thor both commercial and military purposes. In this study, the minimization of the electromagnetic wale reflections using composite layers with different dielectric properties was performed. Dielectric constants were measured for glass/epoxy composites containing conductive carbon blacks and carbon/epoxy fabric composites. Using the measured permittivities of the composites having various carbon black contents, the optimal electromagnetic wave absorbing structure in X-band(8.2GHz-12.4GHz) was determined. The optimal multi-layered composite plates have the thickness of 2.6mm. The maximum reflection loss is -30dB at 10GHz, and the bandwidth haying the absorptivity lower than -l0dB is about 2GHz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.1
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• pp.34-42
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• 2001

The new periodic array structure or frequency selective surface with polarizers characteristic is proposed. The present structure is constructed with two sheets or FSS material, spaced about one-eight wavelength apart, the dipole element orientations of the two sheets being almost perpendicular to each other. The methods of the spectral domain immittance and MoM are used to analyze electromagnetic scattering from this periodic array structure. To confirm the validity of the polrizer's functions or the new periodic array structure, frequency selective surfaces are fabricated, calculated values for the frequency response of the reflection and transmission loss are compared with measured values. Good correspondence has been observed between them. Good axial ratio has been also observed to be achieved in the proposed structure.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.185-190
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• 2015

In this paper we characterized and designed the waveguide antipodal finline transition at 57-65GHz frequency band in V-band for 5G mobile communication systems. Especially, we proposed the design method of spline taper for finline tapers by means of increasing curvature from linear taper. We could perform optimization more effectively by excluding improper regions for optimal performance from optimization using the method. Return losses and insertion losses of antipodal finline transitions were mainly affected by the taper shape of the finline. The resonances in the structure of the finline transition were the strongest enemies who deteriorate the performance of the transition. And we alleviated the resonances using semicircle shaped patch. The designed antipodal finline transition showed good performance as it showed less than -24.2dB of return loss and -0.24dB of insertion loss in the band(57-65GHz) which we suppose to use.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.103-109
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• 2008

In this papaer, a new type of ${\lambda}_g/4$ short stub band pass filter and ${\lambda}_g/2$ open stub band pass filter are purposed. Both are designed using FSCS technique for harmonic suppression. The proposed filters that used FSCS technique and a broadband stop filter is integrated to band pass filter to suppress the harmonics. The BSF are also placed between stubs so that the size is larger than prevent as compared to conventional one. The propose filters have center frequency of 5.8 GHz, bandwidth of 50% and harmonics suppressin is 120% has in bandwith. The measurement results in the case of ${\lambda}_g/4$ short stub filter, insertion loss of 0.5 dB, return loss of 14 dB are achieved and in the case of ${\lambda}_g/2$ open stub filter, loss of 0.8 dB, return loss of 14.4 dB are achieved. The simulation results and the measurement results are almost the same.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.2
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• pp.41-46
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• 2013

In this paper, low pass filters(LPF) using corrugated waveguide for satellite communication is proposed. To design the proposed LPF, the corrugated waveguide and impedance transformers are combined. The corrugated waveguide is formed by arrangement of T-junction. To obtain low insertion loss and high isolation propriety, T-junction is designed by using Chebyshev function. Impedance transformers is designed by combining T-junction with different heights at both ends of the corrugated waveguide to get high return loss. The measured results of the proposed LPF have a return loss of over 35.4 dB, a insertion loss of less than 0.1 dB from 12.25 GHz to 12.75 GHz and a isolation propriety of over 54.5 dB from 14 GHz to 14.5 GHz. From these results, it is confirmed that the proposed waveguide LPF can be used for satellite communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.167-173
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• 2008

In this paper, the flexible narrow bandpass filters (BPFs) with ${\lambda}$g/4 short and ${\lambda}$g/2 open stubs by microstrip line on duroid substrate are suggested. These BPFs with narrow bandwidth show flexible bandwidth with variation of the position of the stubs using the Qe (external quality factor) without changing the impedance value at microwave range. On the other hand, by replacing the series quarter-wavelength connecting lines with the equivalent T-shaped line of bandstop filter(BSF), the compact stub bandpass filter with harmonics suppression can be realized. The BPF with ${\lambda}$g/4 short stubs shows the insertion loss of 2.1 dB and the return loss of 18 dB and BPF with ${\lambda}$g/2 open stubs shows the insertion loss of 1.2 dB and the return loss of 21.9 dB at the center frequency of 5.8 GHz and the bandwidth of 10 %.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.36-36
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• 2007

본 논문에서는 SoP-L(System on Package-Laminates) 기술을 이용하여 이종의 유전율을 가진 유기물 적층 기반의 수동소자를 이용한 GSM/DCS 대역 분리용 diplexer를 설계, 제작하였고 그 특성을 고찰하였다. SoP-L 기술은 LTCC기술과 같은 타 SoP 기술과 비교해서 이종의 물질을 접합하는데 용이하고 공정비용이 저렴하다. 이러한 장점을 이용하여 캐때시터는 유전율 40의 고유전율 재료를 사이에 두고 구성하였고, 인덕터 부문에는 유전율 4률 적용, 정방혈 스파이럴 구조로 두 개 층으로 구성하여 소형화를 이룰 수 있었다. 제작 시에 구리와 유기물을 적층, patterning 하였고, 수직 via hole 을 형성하고 구리의 무전해, 전해 도금 과정을 거쳐 각 소자를 연결하였다. 이러한 과정을 거쳐 제작된 diplexer의 GSM 저역 통과 필터는 0.52 dB이하의 삽입손실과 20 dB 이상의 반사손실을 가지고 DCS 통과 대역 부근에 notch 가 존재하도록 설계함으로써 DCS 통과 대역에서 17 dB 이상의 저지특성을 나타내었다. DCS 고역 통과 필터는 1.2 dB 이하의 삽입손실과 16 dB 이상의 반사손실을 가지며 GSM 통과 대역 부근에 notch를 가지도록 설계하여 GSM 통과대역에서 32 dB 이상의 저지특성을 나타내었다.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.92-96
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• 2003

Dielectric apertures in vertical cavity laser have been used for improved device performance. Numerical analysis is used to estimate the optical losses as the aperture diameter is reduced. The optical losses depend on the aperture size, thickness and location. The optical loss strongly depend on the aperture size and thickness when the aperture size is similar or smaller than the emitted wavelength. The optical loss is negligible and not depend on the aperture thickness when the aperture size is larger than 5 times emitted wavelength.