• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1531-1534
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• 2005

Nano pattern is being utilized to produce micro optical components, sensors, and information storage devices. In this study, a study on nano pattern fabrication using raster-scan type Focused Ion Beam (FIB) milling is introduced. Because the intensity of ion beam has Gaussian distribution, the overlapping of the Gaussian beam results in a 3D pattern, and the shape of the pattern can be adjusted by variation of FIB milling parameters, such as overlap, ion dose, and dwell time. The Gaussian shape of single beam intensity has been investigated by experiment, and 3D nano patterns with pitch of 200nm generated by FIB is demonstrated.

• Current Optics and Photonics
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• 제7권6호
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• pp.701-707
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• 2023

In laser imaging, accurate extraction of the laser's center is essential. Several methods exist to extract the laser's center in an image, such as the geometric mean, the parabolic curve fitting, and the Gaussian curve fitting, etc. The Gaussian curve fitting is the most suitable because it is based on the physical properties of the laser. The width of the Gaussian laser beam depends on the distance from the laser source to the target object. It is assumed in general that the distance remains constant at a laser spot resulting in a symmetric Gaussian model for the laser image. However, on a curved surface of the object, the distance is not constant; The laser beam is narrower on the side closer to the focal point of the laser light and wider on the side closer to the laser source, which causes the distribution of the laser beam to skew. This study presents a modified Gaussian model in the laser imaging to incorporate the slant angle of a curved object. The proposed method is verified with simulation and experiments.

• 한국정밀공학회지
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• 제27권4호
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• pp.102-108
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• 2010

Projection microstereolithography is a process of fabricating a micro-structure by using dynamic mask such as digital micromirror device(DMD). DMD shapes the beam into cross-sectional image of structure. Photocurable resin is cured by the beam and stacked layer on top of layer. It is difficult to deliver the beam from the DMD to the photocurable resin without any distortions. We assume that the beam exposed to the resin by 1 pixel of DMD has Gaussian distribution, so the shaped beam reflected by the DMD affects its neighboring area. Curing pattern corresponding to a cross-sectional images is predicted by superposition of pixels of Gaussian distribution and it is similar to cured shape.

• 비파괴검사학회지
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• 제25권6호
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• pp.467-474
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• 2005

The expanded multi-Gaussian beam model has recently been developed that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field for a phased array transducer with various time delays to achieve steering and/or focusing. The calculation beam fields are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model And then, this study proposes a complete ultrasonic measurement model including the expanded beam model, far-field scattering model and system efficiency, Using the proposed model, phased array ultrasonic testing signals for a flat-bottomed hole with/without focusing were performed.

• 한국전산구조공학회논문집
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• 제13권4호
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• pp.427-436
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• 2000

이 논문은 불규칙 가진력을 받는 회전-고정보의 비선형 응답특성을 나타낸다. 불규칙 가진력은 두 번째 고유모드의 절점과 최대변위점에 가했다. 비선형 편미분 방정식과 경계조건으로 표현되는 이 문제를 Galerkin의 방법을 이용하여 연립 비선형 상미분방정식으로 변환하였다. 이 상미분방정식으로부터 Fokker-Planck방정식과 모멘트 방정식을 얻은 후 Gaussian closure 방법 및 non-Gaussian closure 방법을 이용하여 3 모드 근사시 각각 27개 및 209개의 자율 상미분방정식을 구하였다. Gaussian closure 방법과 non-Gaussian closure 방법으로 2 모드 및 3 모드 근사해석을 수행하였고 해석적 결과들은 Monte Carlo 시뮬레이션 결과와 비교되었다. 해석결과 2 모드 근사해와 3 모드 근사해가 거의 일치하였고 2 모드 내부공진만 고려하여도 해석결과에 별 영향을 주지 않는다는 것을 알 수 있다.

• 한국전자파학회논문지
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• 제26권10호
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• pp.851-868
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• 2015

밀리미터파 및 서브 밀리미터파 전파천문학용 전파망원경은 주로 카세그레인 형태의 안테나를 사용한다. 다양한 전파 천문학 연구를 위해서 한 개의 카세그레인 안테나에 여러 개의 수신대역을 갖는 수신기가 설치된다. 한 개 이상의 수신 대역을 관측하기 위해서는 여러 개의 수신기가 우주전파를 관측할 수 있는 빔 가이딩 시스템이 반드시 필요하게 된다. 이러한 빔 가이딩 시스템은 가우시안 빔 전송이론을 기반으로 준광학 회로로 구성된다. 본 논문에서는 가우시안 빔의 간략한 전송이론을 기반으로 한 가우시안 빔의 변환 방법과 가우시안 빔을 전송하기 위한 빔 전송회로 설계 기법을 제시한다. 이 설계기법을 이용하여 카세그레인 안테나에 적용되는 가우시안 빔 회로 설계와 설계 결과를 기술한다. 마지막으로 준광학 회로 구성부품인 타원면경, 유전체 렌즈 및 혼의 제원 결정에 대하여 기술한다. 제안된 방법을 이용하면 카세그레인 안테나 빔 가이딩 시스템을 간단히 설계할 수 있을 것으로 기대된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.553-560
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• 2001

Recently, ultrasonic testing simulation has becomes very important in the field of nondestructive evaluation due to its unique capability of providing testing signals without real inspection. The ultrasonic testing simulation requires three elementary models including the transducer beam radiation model, the flaw scattering model, and the reception model. In the present work, we briefly describe an approach to develop the ultrasonic testing model together with its elementary models with the multi-gaussian beam model. Based on this approach, we developed ultrasonic testing simulation program with MATLAB. The performance of the developed program is demonstrated by the predicting of ultrasonic signals from two types of flaws, circulars crack and spheres.

• 비파괴검사학회지
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• 제28권6호
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• pp.531-537
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• 2008

One of the fundamental features of time reversal acoustic (TRA) techniques is the ability to focus the propagating ultrasonic beam to a specific point within the test material. Therefore, it is important to understand the focusing properties of a TR device in many applications including nondestructive testing. In this paper, we employ an analytical scheme for the analysis of TR beam focusing in a homogeneous medium. More specifically, a nonparaxial multi-Gaussian beam (NMGB) model is used to simulate the focusing behavior of array transducers composed of multiple rectangular elements. The NMGB model is found to generate accurate beam fields beyond the nonparaxial region. Two different simulation cases are considered here for the focal points specified on and off from the central axis of the array transducer. The simulation results show that the focal spot size increases with increasing focal length and focal angle. Furthermore, the maximum velocity amplitude does not always coincide with the specified focal point. Simulation results for the off-axis focusing cases do demonstrate the accurate steering capability of the TR focusing.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 창립 20주년기념 특별학술발표회
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• pp.111-112
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• 2009

• 한국광학회지
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• 제15권3호
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• pp.200-213
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• 2004

등방성 빔 단면과 비등방성 공간 부분 코히어런스 특성을 갖는 가우시안 셀 모델 빔의 구현에 대하여 연구하였다. He-Ne 레이저의 가우시안 빔이 회전하는 홀로그래픽 확산판을 통과하면서 생성된 확산광을 등방성 빔 단면과 비등방성 공간 코히어런스 특성을 갖는 가우시안 셀 모델 빔으로 만드는 광학계를 제안하였다. 광학계의 해석적 설계 방정식을 유도하였고 이를 사용한 설계 예를 제시하였다.