• International Journal of Contents
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• 제7권4호
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• pp.44-49
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• 2011

The scattering solutions for multiple rectangular metallic gratings in a perfectly conducting plane excited by the TE and TM delta sources are presented using an overlapping T-block method. A reflectarray composed of rectangular metallic gratings shows fanbeam radiation patterns that are useful for an electromagnetic fence. The scattering characteristics of multiple rectangular gratings were computed in terms of total radiated power and antenna directivity. The design method of a fan-beam reflectarray to obtain high directivity was also compared with superdirective radiation and parabolic reflector phase.

• 한국분말재료학회지
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• 제29권4호
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• pp.314-319
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• 2022

The effect of the laser beam diameter on the microstructure and hardness of 17-4 PH stainless steel manufactured via the directed energy deposition process is investigated. The pore size and area fraction are much lower using a laser beam diameter of 1.0 mm compared with those observed using a laser beam diameter of 1.8 mm. Additionally, using a relatively larger beam diameter results in pores in the form of incomplete melting. Martensite and retained austenite are observed under both conditions. A smaller width of the weld track and overlapping area are observed in the sample fabricated with a 1.0 mm beam diameter. This difference appears to be mainly caused by the energy density based on the variation in the beam diameter. The sample prepared with a beam diameter of 1.0 mm had a higher hardness near the substrate than that prepared with a 1.8 mm beam diameter, which may be influenced by the degree of melt mixing between the 17-4 PH metal powder and carbon steel substrate.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 춘계학술대회 논문집
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• pp.490-493
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• 2004

There is great difficulty in machine below 10 micrometers by conventional machining methods, such as micro-EDM. However, ultra micro machining using focused ion beam(FIB) is able to machine to 50 nanometers. Bie ＆ moulds techniques are better than one-to-one machining techniques in regards to production costs in the mass production of ultra size structures. Also, it is advantageous to machine die ＆ moulds to the 10 micrometers level by FIB technique rather than other techniques. It is difficult to machine the three dimensional machining, such as micro lens, using FIB system because of their machining characteristics. In this paper, three dimensional machining techniques were properly introduced, and also experiments showed effectiveness of their techniques.

• 대한방사선기술학회지:방사선기술과학
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• 제39권1호
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• pp.99-105
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• 2016

잡음전력스펙트럼 (noise power spectrum, NPS)는 noise 진폭의 측정과 균일한 방사선 영역으로부터 획득된 영상의 품질에 가장 일반적인 방법 중 하나이다. 이 연구의 목적은 megavoltage X-ray 에너지를 사용하여 다른 잡음 전력스펙트럼 방법론들을 비교하는 것이다. 진단 영역에서의 잡음전력스펙트럼 평가 방법들은 국제 전기 규격 international electro-technical commission(IEC 62220-1) 기준을 사용하여 치료 영역에 적용되었다. 우리가 사용한 전자포털영상장치(electronic portal imaging device, EPID)는 Varian TrueBeam$^{TM}$, Siemens BEAMVIEW$^{PLUS}$, Elekta iViewGT 그리고 Varian Clinac$^R$ iX aS1000이었다. 잡음전력스펙트럼의 관심영역을 측정하기 위해, 우리는 겹침 (overlapping), 비겹침 (non-overlapping), 평탄도 (flatness), 반음영 (penumbra) 4가지 인자를 사용하였다. 결과적으로는 Siemens BEAMVIEW$^{PLUS}$, Varian TrueBeam$^{TM}$ flattening filter, Varian Clinac$^R$ iX aS1000, Varian TrueBeam$^{TM}$ flattening filter free에서의 잡음 (noise) 분포는 기존의 첫번째, 두번째, 세번째 실험방법보다는 Elekta iViewGT보다 현격하게 높은 noise 분포가 나타남을 알 수 있다. 이번 연구는 다양한 인자들이 잡음전력스펙트럼의 megavoltage imaging (MVI)영상에서 MVI영역에서 잡음전력 스펙트럼의 기준의 방법론으로 사용되어질 수 있다는 것을 보여주었다.

• 제어로봇시스템학회논문지
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• 제17권2호
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• pp.79-87
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• 2011

This paper presents the optimal design of an overlapped ultrasonic sensor ring for high resolution obstacle detection of an autonomous mobile robot. It is assumed that a set of low directivity ultrasonic sensors of the same type are arranged along a circle of nonzero radius at a regular spacing with their beams overlapped. First, taking into account the dead angle region, the entire range of obstacle detection is determined with reference to the center of an overlapped ultrasonic sensor ring. Second, the optimal design index of an overlapped ultrasonic sensor ring is defined as the area closeness of three sensing subzones resulting from beam overlap. Third, the lower and upper bounds on the number of ultrasonic sensors are derived, which can guarantee minimal beam overlap and also avoid excessive beam overlap among adjacent ultrasonic sensors. Fourth, employing a commercial low directivity ultrasonic sensor, an optimal design example of an overlapped ultrasonic sensor ring is given along with the ultrasonic sensor ring prototype mounted on top of a mobile robot. Finally, some experimental results using our prototype ultrasonic sensor ring are given to demonstrate the validity and performance of an optimally overlapped ultrasonic sensor ring for high resolution obstacle detection.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.961-969
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• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.463-469
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• 2004

This paper discusses 2D lattice models of beams for simulating the fracture of brittle materials. A simulation of an experiment on a connote beam subjected to bending, in which two overlapping cracks occur, is used to study the effect of individual beam characteristics and different arrangements of the beams in the overall lattice. It was found that my regular orientation of the beams influences the resulting crack patterns. Methods to implement a wide range of poisson's ratios are also developed, the use of the lattice to study arbitrary micro-structures is outlined The crack pattern that n obtained with lattice m in good agreement with the experimental results. Also, numerical simulations of the tests were performed by means of a lattice model, and non-integer dimensions were measured on the predicted lattice damage patterns.

• 대한치과의사협회지
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• 제56권10호
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• pp.538-547
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• 2018

ITK-SNAP (http://www.itksnap.org) and 3D Slicer (CMFreg extension module; www.slicer.org) are open-source softwares which can be used for superimposition of cone-beam CT images. For superimposition, segmentation of bone is done with ITK-SNAP, and then voxel based superimposition of CBCT images can be performed using 3D Slicer. 3D Slicer has various visualization modules which are not provided in common commercial programs. 'Models' module is used to visualize two overlapping three-dimensional images, and this allows various visualizations by changing view mode and color of the model. In addition, differences between two CBCT images can be represented in a color map using 'ShapePopulationViewer' module. This report introduces how to superimpose and visualize CBCT images using ITK-SNAP and 3D Slicer, and the usefulness and limitations of both softwares will be discussed in comparison with commercial softwares.

• Coupled systems mechanics
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• 제6권4호
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• pp.501-522
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• 2017

This paper introduces a numerical procedure to incorporate elasto-plastic local deformation effects in the dynamic analysis of beams. The appealing feature is that simple beam type finite elements can be used for the global model which needs not to be altered by the localized elasto-plastic deformations. An overlapping local sophisticated 2D membrane model replaces the internal forces of the beam elements in the predefined region where the localized deformations take place. An iterative coupling technique is used to perform this replacement. Comparisons with full membrane analysis are provided in order to illustrate the accuracy and efficiency of the method developed herein. In this study, the membrane formulation is able to capture the elasto-plastic material behaviour based on the von Misses yield criterion and the associated flow rule for plane stress. The Newmark time integration method is adopted for the step-by-step dynamic analysis.

• Journal of the Optical Society of Korea
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• 제20권5호
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• pp.593-600
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• 2016

Operation properties, such as output power, beam radius, and crystal temperature rise were investigated in a diode-pumped edge-cooled monolithic Yb:YAG laser with ~ 4 W pumping level. The output power showed saturation behavior because of severe temperature rise and poor spatial overlapping between pump beam and lasing mode. Face cooling geometry by using a sapphire plate was also investigated. No apparent saturation behavior in output power was observed due to the reduced temperature rise, which could be attributed to efficient heat removal through the crystal-sapphire interface.