• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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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.

• Smart Structures and Systems
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• v.22 no.2
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• pp.223-230
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• 2018

This study examines a non-contact laser scanning-based ultrasound system, called an angular scan pulse-echo ultrasonic propagation imager (A-PE-UPI), that uses coincided laser beams for ultrasonic sensing and generation. A laser Doppler vibrometer is used for sensing, while a diode pumped solid state (DPSS) Q-switched laser is used for generation of thermoelastic waves. A high-speed raster scanning of up to 10-kHz is achieved using a galvano-motorized mirror scanner that allows for coincided sensing and for the generation beam to perform two-dimensional scanning without causing any harm to the surface under inspection. This process allows for the visualization of longitudinal wave propagation through-the-thickness. A pulse-echo ultrasonic wave propagation imaging algorithm (PE-UWPI) is used for on-the-fly damage visualization of the structure. The presented system is very effective for high-speed, localized, non-contact, and non-destructive inspection of aerospace structures. The system is tested on an aluminum honeycomb sandwich with disbonds and a carbon fiber-reinforced plastic (CFRP) honeycomb sandwich with a layer overlap. Inspection is performed at a 10-kHz scanning speed that takes 16 seconds to scan a $100{\times}100mm^2$ area with a scan interval of 0.25 mm. Finally, a comparison is presented between angular-scanning and a linear-scanning-based pulse-echo UPI system. The results show that the proposed system can successfully visualize defects in the inspected specimens.

• The Journal of Advanced Prosthodontics
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• v.7 no.4
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• pp.329-337
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• 2015

PURPOSE. This retrospective study aims at the evaluation of implant-supported overdentures (IODs) supported by ceramo-galvanic double crowns (CGDCs: zirconia primary crowns + galvano-formed secondary crown). MATERIALS AND METHODS. In a private practice, 14 patients were restored with 18 IODs (mandible: 11, maxilla: 7) retained by CGDCs on 4 - 8 implants and annually evaluated for technical and/or biological failures/complications. RESULTS. One of the 86 inserted implants failed during the healing period (cumulative survival rate (CSR) implants: 98.8%). During the prosthetic functional period (mean: $5.9{\pm}2.2years$), 1 implant demonstrated an abutment fracture (CSR-abutments: 98.2%), and one case of peri-implantitis was detected. All IODs remained in function (CSR-denture: 100%). A total of 15 technical complications required interventions to maintain function (technical complication rate: 0.178 treatments/patients/year). CONCLUSION. Considering the small sample size, the use of CGDCs for the attachment of IODs is possible without an increased risk of technical complications. However, for a final evaluation, results from a larger cohort are required.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.5
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• pp.396-401
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• 2008

Minimization of processing time in two-photon stereolithography (TPS) has been one of important issues. Generally, a voxel scanning method (VSM) has been used in TPS because the method is very profitable for the stable fabrication irrespective of jittering and response time of scanning equipments such as a stage and a galvano-scanner. However, supplementary processing time due to the on/off control of a shutter for the generation of each voxel is required inevitably in VSM; by this reason, much processing time takes to fabricate largescale micropatterns and three-dimensional patterns. In this work, a continuous scanning method (CSM), generating patterns by movement of beam focus with a constant speed, is proposed for the improvements of scanning speed and precision in TPS. Some line patterns are fabricated by each scanning method to demonstrate the usefulness of CSM with viewpoints of scanning speed and precision.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.576-580
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• 2005

New real-time confocal microscopy using spectral encoding technique and slit confocal aperture is proposed and designed. Spectral encoding technique, which encodes one-dimensional spatial information of a specimen in wavelength, and slit aperture make it possible to obtain two-dimensional lateral image of the specimen simultaneously at standard video rates without expensive scanning units such as polygon mirrors and galvano mirrors. The working principle and the configuration of the system are explained. The variation in axial responses for the simplified model of the system with normalized slit width is numerically analyzed based on the wave optics theory. Slit width that directly affects the depth discrimination of the system is determined by a compromise between axial resolution and signal intensity from the simulation result. On the assumption of the lateral sampling resolution of 50 nm, design variables and governing equations of the system are derived. The system is designed to have the mapping error less than the half pixel size, to be diffraction-limited and to have the maximum illumination efficiency. The designed system has the FOV of $12.8um{\times}9.6um$, the theoretical axial FWHM of 1.1 um and the lateral magnification of-367.8.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.693-699
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• 2020

355nm UV pulse laser is irradiated on the surface of polyimide (PI) by LDW (Laser Direct Writing) method to produce a high sensitivity flexible humidity sensor using a simple one-step process. The LDW method continuously investigates 2-D CAD data using a galvano scanner and an F-lens. This method is non-contact, so it minimizes physical strain on the PI. Laser-induced graphene (LIG) produced by lasers has a high surface area due to its high flexibility and numerous pores and oxidizers compared to conductors. For this reason, it is highly useful as a flexible humidity sensor. The humidity sensor produced in this study was attached to the inside of a mask filter, which has become a hot topic recently, and its applicability was confirmed.The measurement of humidity measured the sensitivity, reactivity, stability and recovery behavior of the sensor by measuring changes in capacitance and resistance.

• Transactions of the Society of Information Storage Systems
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• v.7 no.1
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• pp.19-24
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• 2011

Holographic Data Storage System, one of the next generation data storage devices, is a 2-dimensional page oriented memory system using volume holograms in writing and retrieving process. Recently photopolymer with disc type substrate was selected as a media for the Holographic Data Storage System. The disc tilt occurs when the media rotates and the external disturbance applies. The disc tilt causes the change of the angle between the reference beam and the media, the data cannot be retrieved with the right angle or other data page is retrieved. The tilt is generated in a 2-axis direction (tangential, radial). The tangential tilt direction is the same with the multiplexing plane, while the radial tilt direction is a perpendicular to the multiplexing plane. In this research we propose 2-axis tilt angle servo system. The tilt errors are measured by using external photo detector and the additional red laser. Then the tangential direction tilt is compensated by using the galvano mirror. Also the radial direction tilt is compensated by the rotating prism between the relay lens in the reference field. Finally we confirm the compensation results through the Signal to Noise Ratio(SNR) and Bit Error Rate(BER).

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.11
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• pp.979-983
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• 2013

The three-dimensional measurement method of confocal systems is a spot scanning method which has a high resolution and good illumination efficiency. However, conventional confocal systems had a weak point in that it has to perform XY axis scanning to achieve FOV (Field of View) vision through spot scanning. There are some methods to improve this problem involving the use of a galvano mirror [1], pin-hole array, etc. Therefore, in this paper we propose a method to improve a parallel mode confocal system using a micro-lens and pin-hole array in a dual microscope configuration. We made an area scan possible by using a combination MLA (Micro Lens Array) and pin-hole array, and used an objective lens to improve the light transmittance and signal-to-noise ratio. Additionally, we made it possible to change the objective lens so that it is possible to select a lens considering the reflection characteristic of the measuring object and proper magnification. We did an experiment using 5X, 2.3X objective lens, and did a calibration of height using a VLSI calibration target.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.2
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• pp.61-67
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• 2022

A metal salt solution was prepared from valuable metals (Ni, Co, Mn) recovered from a scrap of waste lithium secondary batteries, and an NCM811 precursor was synthesized from the solution. The effect on precursor formation according to reaction time was confirmed by SEM, PSA, and ICP analysis. Based on the analysis results, the electrochemical properties of the synthesized NCM811 precursor and the commercial NCM811 precursor were investigated. The Galvano charge-discharge cycle, rate performance, and Cycle performance were compared, and as a result, there was no significant difference from commercial precursors.

• Journal of the Korean Electrochemical Society
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• v.13 no.2
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• pp.116-122
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• 2010

A $Cu_3Si$ film electrode is obtained by Si deposition on a Cu foil using DC magnetron sputtering, which is followed by annealing at $800^{\circ}C$ for 10 h. The Si component in $Cu_3Si$ is inactive for lithiation at ambient temperature. The linear sweep thermammetry (LSTA) and galvano-static charge/discharge cycling, however, consistently illustrate that $Cu_3Si$ becomes active for the conversion-type lithiation reaction at elevated temperatures (> $85^{\circ}C$). The $Cu_3Si$ electrode that is short-circuited with Li metal for one week is converted to a mixture of $Li_{21}Si_5$ and metallic Cu, implying that the Li-Si alloy phase generated at 0.0 V (vs. Li/$Li^+$) at the quasi-equilibrium condition is the most Li-rich $Li_{21}Si_5$. However, the lithiation is not extended to this phase in the constant-current charging (transient or dynamic condition). Upon de-lithiation, the metallic Cu and Si react to be restored back to $Cu_3Si$. The $Cu_3Si$ electrode shows a better cycle performance than an amorphous Si electrode at $120^{\circ}C$, which can be ascribed to the favorable roles provided by the Cu component in $Cu_3Si$. The inactive element (Cu) plays as a buffer against the volume change of Si component, which can minimize the electrode failure by suppressing the detachment of Si from the Cu substrate.