• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.187-190
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• 2001

A new ultrasound imaging technique based on simultaneous multiple transmit focusing using orthogonal modified Golay codes is presented. modified Golay codes are used to increase signal-to-noise-ratio(SNR) and maximize the transmit power efficiency(TPE). Conventional Golay codes consist of a pair of complementary codes with same length and can be compressed into a delta-like signal due to their complementary property. In the present work, two modified Golay codes focused at different depths are transmitted at the same time, which are mutually orthogonal. On receive, these orthogonal modified Golay codes are separately compressed into two short pulses and individually focused. These two focused beam are combined to form a frame of image with improved lateral resolution. Computer simulations are performed to verity the proposed method improves the lateral resolution of image compared with the conventional echo system.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.96-100
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• 2007

Condenser lens and objective lens are used to demagnify the image of the crossover to the final spot size. In lens, electrons are focused by magnetic fields. This fields is fringing field. It is important in electron focusing. Electron focusing occurs the radial component field and axial component field. Radial component produces rotational force and axial component produces radial force. Radial force causes the electron's trajectory to curve toward the optic axis and corss it. Focal length decreases as the current of lens increases. In this paper, we use the focal length for desiging the hardware of lens current control and present the results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.792-798
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• 2012

This study shows the vibration characteristics of an actuator with six wire-suspensions, used in optical pickups of optical disc drives (ODDs). In this paper, the vibration characteristics of this beam structure is induced mathematically. To obtain vibration modes of focusing direction, the vibration analysis is achieved in lateral and longitudinal directions of the structure. The accuracy of induced vibration characteristics is proved by comparing mode frequencies with a finite element analysis. Finally, it is shown that mode shapes can be modified by changing design parameters in mathematical expressions.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.193-196
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• 2003

We have developed a laser welding monitoring system to monitor laser welding process conditions such as sample feed rate, laser focal position, and laser power. A 2 ㎾ Nd:YAG CW laser beam has been applied to the welding of a stainless steel plate (SUS306) to investigate the welding monitoring. Theradiation signal from the weld pool was guided back through the focusing optics and the laser delivery fiber, and measured by a photo detector. By changing the focus of the laser beam along the z-direction, the penetration depth of the welding material has been measured. That shows the penetration depth depends on the frequency fluctuations of the plume signals which can be used in welding quality control.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.104-107
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• 2002

Direct Metal Manufacturing (DMM) is a new additive process that aims to take die making and metalworking in an entirely new direction. It is the blending of five common technologies : lasers, computer-aided design (CAD), computer-aided manufacturing (CAM), sensors and powder metallurgy. The resulting process creates parts by focusing an industrial laser beam onto a tool-steel work piece or platform to create a molten pool of metal. A small stream of powdered tool-steel metal is then injected into the melt pool to increase the size of the molten pool. By moving the laser beam back and forth, under CNC control, and tracing out a pattern determined by a computerized CAD design, the solid metal part is built line-by-line, one layer at a time. DMM produces improved material properties in less time and at a lower cast than is possible with traditional fabrication.

• Korean Institute of Interior Design Journal
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• no.13
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• pp.203-215
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• 1997

This Study typed the roof-design in analysis of structural design of the glulam architecture, developed worldwidely, nowaday. For this, it is studied the characters of glulam as the history of glulam architectures, manufacture of glulam, shapes and section of glulam, fireproof and combution of glulam. And it is studied roof-design according to structural type of glulam roof-structure. Conclusively, types of glulam roof design typied as 1)the Simple Beam str., 2)the Multi-Joints continous Beam str. 3)the Hinge str. 4)the Rahmen str. 5)the Archi str. 6)the Grid str. 7)etc str. (Folded-plate str., Radial str., Cylinder Shell str., Ring Dome str., Geodesic Dome str., Conic Coloid Shell str., H.P Shell str. Cantilever Shell str.)

• Journal of KSNVE
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• v.6 no.6
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• pp.763-770
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• 1996

This paper proposes a method to determine the initial shape and size of the suspension beam of an optical pickup actuator subjected to specified dynamic characteristics. For the analysis, a simplified model consisting of a concentrated mass, rotational springs and beams is developed. Based on this model, the key dimensionless design parameters are introduced, which govern low-frequency vibration characteristics i. e., the resonant frequencies in the tracking and focusing directions. A systematic procedure for sizing and shaping the actuator suspension beams is described and applied to a sample case. The effectiveness of the present technique is verified through the comparison of the present and the finite element results.

• Proceedings of the Optical Society of Korea Conference
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• 2007.02a
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• pp.68-69
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• 2007

In this paper, the spatial and spectral characteristics of an optical demultiplexer based on a chirp volume holographic grating are presented. The chirp grating is recorded by illuminating the photopolymer film under the interference of a convergent beam and divergent beam. The dependence of the spatial distance on the grating-focusing lens separation is observed. The bandwidth and the crosstalk between two channels with 0.4-nm spectral interval are 0.13 nm and 12 dB, respectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.54-58
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• 2008

Time reversal (TR) of body waves in fluids and isotropic solids has been used in many applications including ultrasonic NDE. However, the study of the TR method for anisotropic materials is not well established. In this paper, the full reconstruction of the input signal is investigated for anisotropic media using an analytical formulation, called a modular Gaussian beam (MGB) model. The time reversal operation of this model in the frequency domain is done by taking the complex conjugate of the Gaussian amplitude and phase received at the TR mirror position. A narrowband reference signal having a particular frequency and number of cycles is then multiplied and the whole signal is inverse Fourier transformed. The original input signal is seen to be fully restored by the TR process of MGB model and this model can be more generalized to simulate the spatial and temporal focusing effects due to TR process in anisotropic materials.

• 연구논문집
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• s.25
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• pp.105-113
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• 1995

Fresnel lenses are developed for flat optics with the optical characteristics close to aspherical lens such as sharp focusing and dispersion instead of spherical or aspherical surface. Usually, these fresnel lenses and diffraction gratings are machined by high-energy beam such as electron beam machining, but recently with the development of ultra precision machine tool and machining technology, 3-dimension micro machining becomes preferable. This study on the micro machining of fresnel lens is carried out to develop the basic technology of ultra precision micro machining. The machined lens mold will be used for the manufacturing of fresnel lens with 120mm focal distance using synthetic resin material with 1.49 refractive index(PMMA), and the shape of lens is 48mm diameter, $300\mum$ pitch and about $5-700\mum$depth of groove in brass.