• 대한기계학회논문집
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• 제19권4호
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• pp.950-967
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• 1995

Acoustic holography makes it possible to reconstruct the acoustic field based on the measurement of the pressure distribution on the hologram surface. Because of the merit that one can obtain an entire three-dimensional wave field from the data recorded on a two-dimensional surface, the holographic method has been widely studied. Being an experimental method, holography has an unavoidable error which is generate by sampling in space and frequency domain and finite aperture size. Its magnitude is dependent on the space and frequency domain and finite aperture size. Its magnitude is dependent on the shape of hologram surface, acoustic holography may be classified into four types of holography : rectangular type planeholography, circular type plane holography, cylindrical holography and spherical holography. In this paper, four types of holography are studied by modal summation method. Numerical simulation is performed using a monopole source with varying parameters to find out effects to the estimation error in each holography. Experiments of circular type plane holography and cylindrical holography explain strong relation between the shape of hologram surface and the acoustic field.

• 한국전자파학회논문지
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• 제19권2호
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• pp.237-243
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• 2008

본 논문에서는 무한히 넓은 백 플레인의 사각형 개구를 관통하는 길이가 다른 평행 2선 전송 선로에 대하여 백 플레인의 존재가 전송 선로에 미치는 영향을 검토하였다. 이론 해석에는 FDTD법을 사용하였으며, 길이가 다른 구조를 가지게 하는 부가 선로의 길이와 전송 선로의 간격 변화에 따른 반사 손실 및 삽입 손실 특성을 계산하여 백 플레인이 전송 선로에 미치는 영향을 고찰하였다. 그 결과, 전송 선로의 간격이 좁은 경우에는 부하 측의 전송 선로가 안테나처럼 동작하여 삽입 이득 특성이 나타나고, 부가 선로의 길이가 길어지면 백 플레인에 의한 삽입 손실 특성이 현저히 나타남을 확인할 수 있었다. 반사 손실을 측정하고 수치 계산 결과와 비교하여 이론 해석의 타당성도 확인하였다.

• 한국전자파학회논문지
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• 제12권7호
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• pp.1175-1181
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• 2001

본 논문에서는 도파관 안에 전파의 진행에 대해 단면 방향으로 놓인 임의의 모양의 iris를 해석하기 위한 효율적인 반복 유한 요소법을 제안하였다. 불연속 구조 부근의 적은 숫자의 요소만으로도, 몇 번의 경계 조건의 수정 과정을 통해 전형적인 유한 요소법으로 정확한 해를 구할 수 있음을 보였다. 제안한 방법의 타당성을 보이기 위해, 구형 도파관 내의 원형 iris를 해석하고 유한 요소 경계 적분법을 이용한 결과와 비교하였다.

• ALGAE
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• 제27권4호
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• pp.235-247
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• 2012

Regardless of continuous researches, recent researches on the genus Eucampia (Bacillariophyceae) have focused mainly on E. zodiacus f. zodiacus In the present study, species of the genus Eucampia have been studied based on their morphological characteristics. Eucampia species were collected at 24 sites from July 2008 to June 2011 in Korean coastal waters. Species were mainly identified based on the shape of valve, ocellus, and aperture, along with the length and shape of the bipolar elevations. As a result, five Eucampia species were identified: Eucampia cornuta, E. groenlandica, E. zodiacus f. zodiacus, E. zodiacus f. cylindrocornis, and E. zodiacus var. cornigera. E. cornuta and E. groenlandica have long pervalvar axis length, but the others display short or moderate length. Ocellus shape of E. cornuta, E. groenlandica and E. zodiacus f. cylindrocornis are linear ribs, whereas E. zodiacus f. zodiacus and E. zodiacus var. cornigera have radial ribs with central area. E. cornuta and E. zodiacus f. cylindrocornis have long and narrow cylindrical elevations. E. groenlandica and E. zodiacus f. zodiacus have short and broad elevations with blunt tips. E. zodiacus var. cornigera has long and broad conical elevations. In terms of aperture shape, E. cornuta has large elliptical form, E. groenlandica has almost circular to rounded rectangular form, E. zodiacus f. zodiacus has narrow and elliptical rounded rectangular to a narrow lanceolate form, E. zodiacus f. cylindrocornis has almost rectangular form, and E. zodiacus var. cornigera has rounded rhombic form. On the basis of elevations in broad girdle view, 5 Eucampia taxa could be divided into 3 types: 'narrow H type', E. cornuta and E. groenlandica; 'regular H type', E. zodiacus f. cylindrocornis and E. zodiacus var. cornigera (partial); 'wide H type', E. zodiacus f. zodiacus (almost).

• 한국전자파학회논문지
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• 제21권9호
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• pp.1056-1064
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• 2010

본 논문에서는 백 플레인의 개구를 관통하는 대칭 전송 선로 구조를 해석하기 위한 근사 해석법을 제안하고 있다. 제안된 방법은 백 플레인의 개구면 임피던스를 모멘트 법으로 계산하고, 이 값을 전송 선로에 병렬로 연결한 근사 등가 전송 선로를 해석하여 삽입 손실 특성을 계산하는 방법이다. 근사 해석법을 적용하여 계산한 결과, 정합이 되었을 때는 관통하는 전송 선로와 개구가 가까울수록 특정 주파수에서 삽입 손실이 증가하며, 부정합된 경우에는 특정 주파수에서 삽입 이득 현상이 나타나고 있다. 또한, 개구의 가로 길이가 세로 길이보다 전송 선로에 더 큰 영향을 미친다는 것도 확인하고 있다. 근사 해석법의 타당성을 검증하기 위해, 근사 해석법으로 계산된 삽입 손실 특성을 실험치 및 상용툴의 계산 결과와도 비교하였다.

• 한국전자파학회논문지
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• 제14권5호
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• pp.479-488
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• 2003

시간영역 유한차분법을 이용하여 2.4 GHz와 5.8 GHz외 ISM 대역을 위한 이중대역 마이크로스트립 안테나를 설계한다. 2개의 구형 패치가 겹쳐진 십자형 패치를 안테나의 방사소자로 제안하고 급전 방식은 개구 결합을 이용한다. 안테나 설계를 위해 개구와 스터브 길이 변화에 따른 입력 임피던스의 변화를 살펴보고, 방사소자의 길이와 폭 변화에 따른 중심 주파수와 -10 dB대역폭을 고찰한다 반사손실에 대한 계산 결과를 IE3D의 해석 결과 및 측정 결과와 비교하여 잘 일치함을 확인하고, 주파수 2.43 GHz와 5.79 GHz에서 안테나의 방사패턴을 측정하여 -3 dB 빔폭, 전후방비 및 최대 이득을 제시한다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제27권1호
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• pp.56-74
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• 2023

In order to obtain practical and high-quality satellite images containing high-frequency components, a large aperture optical system is required, which has a limitation in that it greatly increases the payload weight. As an attempt to overcome the problem, many multi-aperture optical systems have been proposed, but in many cases, these optical systems do not include high-frequency components in all directions, and making such an high-quality image is an ill-posed problem. In this paper, we use deep learning to overcome the limitation. A deep learning model receives low-quality images as input, estimates the Point Spread Function, PSF, and combines them to output a single high-quality image. We model images obtained from three rectangular apertures arranged in a regular polygon shape. We also propose the Modulation Transfer Function Loss, MTF Loss, which can capture the high-frequency components of the images. We present qualitative and quantitative results obtained through experiments.

• 대한전자공학회논문지
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• 제26권11호
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• pp.1752-1758
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• 1989

For many different types of apertures the diffraction phenomenon on the electromagnetic wave is analyzed by unsing Kirchhoff and Fresnel's diffraction theory. The signal intensity in variation of aperture's parameters is numerically calculated by a computer. To obtain the experimental data many types of apertures were made on an acryl board on which a special materical Elecoat was painted for preventing some reflections on the board surface and transmissions through it. Two Yagi antennas were used for a transmitting and receiving antenna and the frequency was 820MHz. The theoretichal values agreed reasonably with experimental data and these results will be used for a system design in the mobile communication between many buildings in the middle of a city.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2002년도 종합학술발표회 논문집 Vol.12 No.1
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• pp.241-245
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• 2002

Dual-band microstrip antenna is designed for industrial-scientific-medical(ISM) band of 2.4㎓ and 5.8㎓ using finite-difference time-domain method(FDTD). Cross Patch fed by aperture in the ground plane of microstrip line is proposed as radiation element of antenna, which is 2 rectangular Patch is overlapped. To design antenna, change of input impedance by aperture and stub length change is examined. And it is investigated that center frequency and -10 ㏈ bandwidth by Length of radiation element and width change. Experimental result about reflection Loss confirmed that agree well with analysis results of FDTD and IE3D, And -3 ㏈ beam width, front to back ratio and gain in frequency 2.43㎓ and 5.79㎓ is presented by measuring radiation Pattern of antenna.

• Journal of electromagnetic engineering and science
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• 제1권1호
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• pp.43-47
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• 2001

A compact size microstrip antenna element using FR-4 substrate is proposed for use in repeater and base stations. Two stacked patches are aperture-coupled by two split feedlines. Rectangular stubs on the split feedlines are laid under the aperture and have the effect of considerably lowing the magnitude of $S_{11}$ [dB] and broadening impedance bandwidth. The designed structure has been fabricated and measured. Based on 20 dB, the return loss bandwidth is about 16.8% (1.86 GHz~2.20 GHz), which covers the frequency range assigned for IMT-2000 with a large margin. The overall dimension of the proposed antenna structure is 37 mm$\times$41 mm$\times$19mm (very compact). The antenna gain is more than 7.5 dBi over the required frequency range.