• 한국기계가공학회지
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• 제11권1호
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• pp.62-67
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• 2012

Recently UV laser is widely used to process micro parts using various materials such as polymers, metals and ceramics because it has a very high intensity at the focused spot area. It is generally known that there are still some difficulties for alumina($Al_2O_3$) ceramics to directly make micro patterns like holes and lines on the surface of working material using 355nm UV laser because the alumina has a very low absorption coefficient at that wavelength. But nowadays new alumna with nano-porous holes is developed and applied to advanced micro functional parts of IT, BT and BT industries. In this paper, we are going to show the mechanism of photo-thermal ablation for nano-porous ceramics. Inside hole there is a lot of multiple reflections along the depth of hole. Experimentally we can find the micro hole drilling and micro grooving on the surface of nano-porous alumina.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.29-32
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• 2008

In this paper, we propose one unsupervised classification technique using the degree of polarization (DoP) and the co-polarized phase-difference (CPD) statistics, instead of the entropy and alpha. It is shown that the DoP is closely related to the entropy, and the CPD to the alpha. The DoP explains the feature how much the effect of multiple reflections is contained. Hence, the DoP could be used as an important factor for classifying classes. The CPD can also be computed from the measured Mueller matrix elements. For the smooth surface scattering, the CPD is about $0^{\circ}$, and for dihedral-type scattering, the CPD is about $180^{\circ}$. A DoP-CPD diagram with appropriate boundaries between six different classes is developed based on the SAR image. The classification results are compared with the existing Entropy-alpha diagram as well as the IPL-AirSAR polarimetric data. The technique may have capability to classify an SAR image into six major classes; a bare surface, a village, a crown-layer short vegetation canopy, a trunk-layer short vegetation canopy, a crown-layer forest, and a trunk-dominated forest. Based on the DoP and CPD analysis, a simple three-component decomposition technique was also proposed.

• Journal of electromagnetic engineering and science
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• 제17권4호
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• pp.241-243
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• 2017

In this paper, we have presented an equation for estimating the gain of a Fabry-Perot cavity (FPC) antenna with a finite dimension. When an FPC antenna has an infinite dimension and its height is half of a wavelength, the maximum gain of that FPC antenna can be obtained theoretically. If the FPC antenna does not have a dimension sufficient for multiple reflections between a partially reflective surface (PRS) and the ground, its gain must be less than that of an FPC antenna that has an infinite dimension. In addition, the gain of an FPC antenna increases as the dimension of a PRS increases and becomes saturated from a specific dimension. The specific dimension where the gain starts to saturate also gets larger as the reflection magnitude of the PRS becomes closer to one. Thus, it would be convenient to have a gain equation when considering the dimension of an FPC antenna in order to estimate the exact gain of the FPC antenna with a specific dimension. A gain versus the dimension of the FPC antenna for various reflection magnitudes of PRS has been simulated, and the modified gain equation is produced through the curve fitting of the full-wave simulation results. The resulting empirical gain equation of an FPC antenna whose PRS dimension is larger than $1.5{\lambda}_0$ has been obtained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.418-429
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• 2011

Researches using time reversal acoustics (TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of the plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric (PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

• 대한전자공학회논문지
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• 제21권5호
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• pp.17-26
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• 1984

본 논문은 탄성표면파를 이용한 소형 TV중간주파 필터의 설계 및 제작과정을 보고한다. 초기의 원하는 임펄스응답을 얻기 위해 윈도우잉 (windowing) 방법 및 주파수 샘플링 방법이 제안되어 시간축샘플링 방법과 비교 연구되었으며, 트랩부근에서 원하는 특성을 얻기 위해 회절영향이 보상되었다. 다중 반사를 줄이고 비대칭 특성을 얻기 위해 4f0샘플링 기법을 사용하였으며, 효과적인 사진부식 방법을 사용하여 11.2㎛의 폭을 갖는 양호한 핑거가 얻어겼다. 본 연구는 SAW 필터의 국산화라는 차원에서. 요구하는 사양을 만족시킬 수 있고, 양산성이 있는 크기를 가진 제품을 개발하였음을 보고한다.

• 한국초전도ㆍ저온공학회논문지
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• 제21권4호
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• pp.13-18
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• 2019

Superconducting junctions of topological insulator (TI) are expected to host Majorana bound state, which is essential for developing topological quantum information devices. In this study, we fabricated Josephson junctions (JJs) made of Sb-doped Bi2Se3 TI nanoribbon and PbIn superconducting electrodes. In the normal state, the axial magnetoresistance data exhibit periodic oscillations, so-called Aharonov-Bohm oscillations, due to a metallic surface state of TI nanoribbon. At low temperature of 1.5 K, the TI JJ reveals the superconducting proximity effects, such as the critical current and multiple Andreev reflections. Under the application of microwave, integer Shapiro steps are observed with satisfying the ac Josephson relation. Our observations indicate that highly-transparent superconducting contacts are formed at the interface between TI nanoribbon and conventional superconductor, which would be useful to explore Majorana bound state in TI.

• 한국음향학회지
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• 제32권3호
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• pp.237-246
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• 2013

본 논문에서는 캐비테이션 터널에서의 소음계측용 청음기 배열 설계를 위한 최적화 기법을 제안하였다. 제안된 최적설계 기법은 배열 설계인자 및 목적함수 정의 그리고 최적화 알고리즘 적용 등의 내용으로 구성되어 있다. 설계인자 정의는 원형배열, 나선배열, 다중나선배열을 대상으로 하였다. 목적함수는 주엽의 빔폭과 최대 부엽 크기를 동시에 고려할 수 있도록 정의하였다. 최적화 알고리즘으로는 광역 최적화 기법의 일종인 VFSR 기법을 적용하였다. 최적 설계기법을 각 배열에 적용 후 도출된 최적 배열을 대상으로 최대 부엽크기 및 주엽의 빔폭을 분석하였다. 끝으로 캐비테이션 터널 내부의 다중반사를 고려한 빔형성 결과 평가를 통해 본 기법의 유용성을 확인하였다.

• 한국군사과학기술학회지
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• 제21권2호
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• pp.147-157
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• 2018

There are increasing demands to provide early warning against intruding drones and cope with potential threats. Commercial anti-drone systems are mostly based on simple target detection by radar reflections. In real scenario, however, it becomes essential to obtain drone radar signatures so that hostile targets are recognized in advance. We present experimental test results that micro-Doppler radar signature delivers partial information on multi-rotor platforms and exhibits limited performance in drone recognition and classification. Afterward, we attempt to generate high resolution profile of flying drone targets. To this purpose, wide bands radar signals are employed to carry out inverse synthetic aperture radar(ISAR) imaging against moving drones. Following theoretical analysis, experimental field tests are carried out to acquire real target signals. Our preliminary tests demonstrate that high resolution ISAR imaging provides effective measures to detect and classify multiple drone targets in air.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 Asia Navigation Conference
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• pp.71-78
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• 2006

The image of an object obtained by the radar is not corresponding to its true shape, because the image of an object observed by the radar is receiving an influence such as multiple-reflections and expanded in bearing because of the beam width of a radar. In addition, a radio wave does not hit the entire surface of an object. Therefore, the image of the front side of a ship facing a radar antenna corresponds to its true shape. In this paper, a method to estimate a ship's shape by means of the integration of the front parts of images obtained from radars is proposed. In addition, a matter, which is observation error of each radar, in using multi-radars, and the process included in the proposed method for solving the matter, are described. As a result of the experiment, the accuracy of about 3 degrees in ship's heading and about 14 meters in length and about 9 meters in beam was obtained.

• Applied Science and Convergence Technology
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• 제26권6호
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• pp.208-213
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• 2017

Flexible opto-electronic devices are developed on the insulating layer deposited stainless steel (STS) substrates. The silicon dioxide ($SiO_2$) material as the diffusion barrier of Fe and Cr atoms in addition to the electrical insulation between the electronic device and STS is processed using the plasma enhanced chemical vapor deposition method. Noble silver (Ag) films of approximately 100 nm thickness have been formed on $SiO_2$ deposited STS substrates by E-beam evaporation technique. The films then were annealed at $650^{\circ}C$ for 20 min using the rapid thermal annealing (RTA) technique. It was investigated the variation of the surface morphology due to the interaction between Ag films and $SiO_2$ layers after the RTA treatment. The results showed the movement of Si atoms in silver film from $SiO_2$. In addition, the structural investigation of Ag annealed at $650^{\circ}C$ indicated that the Ag film has the material property of p-type semiconductor and the bandgap of approximately 1 eV. Also, the films annealed at $650^{\circ}C$ showed reflection with sinusoidal oscillations due to optical interference of multiple reflections originated from films and substrate surfaces. Such changes can be attributed to both formation of $SiO_2$ on Ag film surface and agglomeration of silver film between particles due to annealing.