• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.720-725
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• 2000

A new ultrasonic pulse-echo technique was developed and described for vibration measurement of the suspension assembly in hard disk drives. The method is based upon the difference in magnitude of two consecutive reflection waves from a moving object(suspension), while the traditional ultrasonic vibrometer uses the phase shift of the reference wave and the reflection wave. A cone-shape delay line is designed to access the small structure. A simple mathematical model is presented and analyzed with experimental results to show the feasibility of the method. The advantages of this ultrasonic vibration measurement method are relatively high resolution, low cost, and ease of implementation comparing with the Laser Doppler vibrometer.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.3-19
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• 2005

Novel optical techniques are presented for three-dimensional tracking of nanoparticles; Optical Serial Sectioning Microscopy (OSSM) and Ratiometric Total Internal Reflection Fluorescent Microscopy (R-TIRFM). OSSM measures optically diffracted particle images, the so-called Point Spread Function (PSF), and dotermines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. The line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids. On the other hand, R-TIRFM is presented to experimentally examine the classic theory on the near-wall hindered Brownian diffusive motion. An evanescent wave field from the total internal reflection of a 488-nm bandwidth of an argon-ion laser is used to provide a thin illumination field of an order of a few hundred nanometers from the wall. The experimental results show good agreement with the lateral hindrance theory, but show discrepancies from the normal hindrance theory. It is conjectured that the discrepancies can be attributed to the additional hindering effects, including electrostatic and electro-osmotic interactions between the negatively charged tracer particles and the glass surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.408-413
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• 1995

We investigated the effect of mechanical backside damage upon minority carrier recombination lifetime measurement in Czochralski silicon substrate by laser excitation/microwave reflection photoconductance decay method. The intensity of mechanical damage was evaluated by X-ray double crystal rocking curve, X-ray section topography and wet oxidation/preferential etch methods. The data indicate that the higher the mechanical damage intensity, the lower the minority carrier lifetime, and the threshold full width at half maximum value which affect minority carrier lifetime measurement is about 13 secs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1862-1870
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• 1997

A fast and precise technique to measure 3-dimensional coordinates of an object is proposed. It is essential to take the 3-dimensional measurements of the object in design and inspection. Using this developed system a surface model of a complex shape can be constructed. 3-dimensional world coordinates are projected onto a camera plane by the perspective transformation, which plays an important role in this measurement system. According to the shape of the object two measuring methods are proposed. One is rotation of an object and the other is translation of measuring unit. Measuring speed depending on image processing time is obtained as 200 points per second. Measurement resolution i sexperimented by two parameters among others; the angle between the laser beam plane and the camera, and the distance between the camera and the object. As a result of these experiments, it was found that measurement resolution ranges from 0.3mm to 1.0mm. This constructed surface model could be used in manufacturing tools such as rapid prototyping machine.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.65-70
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• 2007

Generally, the core component of small precise optical device demands high accuracy of manufacturing processes. Although, the geometry of it is simple, the manufacturing technique to materialize is categorized as the ultra-precision machining and it must be done with the specialized machines and by the trained operator. Typical examples of small precise optical device are laser printer and phone camera. As a core part of laser printer, polygon mirror is used in laser scanning unit(LSU). It couldn't be fabricated with conventional machine but specified machine for polygon mirror machining. In this study, Polygon mirror with 16 surfaces was manufactured in the process of ultra-precision fly-cutting with Al material and investigated optimum machining conditions in terms of feedrate, pitch per cycle and depth of cut. Owing to process of polishing has bad influence on reflection angle, surface roughness, $R_{max}$=10nm, and form error, $Ra={\lambda}/10({\lambda}=632nm)$, are prerequisites for polygon mirror.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.654-659
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• 2001

A new non-contact method of the frost thickness measurement has been developed. The method is based on the digital image processing technique to identify the reflection edge of the image captured by a CCD camera under laser sheet light illumination. To insure the accuracy of frost layer thickness, an in-situ calibration procedure is carried out with a calibration target with 0.5mm holes. Using the mapping function obtained by the calibration procedure, the contour of frost surface can be estimated with sub-pixel resolutions. The developed method is applied to study the effect of cooling plate temperature on the frost thickness in a small low speed wind tunnel.

• The korean journal of orthodontics
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• v.29 no.2 s.73
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• pp.165-181
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• 1999

Treatment mechanics should be individualized to be suitable for each patient's personal teeth and anatomic environment to get a best treatment result with the least harmful effects to teeth and surrounding tissues. Especially, the change of biomechanical reaction associated with that of the centers of resistance of teeth should be considered when crown-to-root ratio changed due to problematic root resorption and/or periodontal disease during adult orthodontic treatment. At the present study, in order to investigate patterns of initial displacements of anterior teeth under certain orthodontic force when crown-to-root ratio changed in not only normal periodontal condition but also abnormal periodontal and/or teeth condition, the changes of the centers of resistance for maxillary and mandibular 6 anterior teeth as a segment were studied using the laser reflection technique, the lever & pulley force applicator and the photodetector with these quantified variables reducing alveolar bone 2mm by 2mm for each of maxillary 6 anterior teeth until the total amount of 8mm and root 2mm by 2mm for each of mandibular 6 anterior ones until the total amount of 6mm. The results were as follows: 1. Under unreduced condition, the center of resistance during initial displacement of maxillary 6 anterior teeth was located at the point of about $42.4\%$ apically from cemento-enamel junction(CEJ) of the averaged tooth of them and kept shifting to about $76.7\%$ with alveolar bone reduction. 2. The distance from the averaged alveolar crest level of maxillary 6 anterior teeth to the center of resistance for the averaged tooth of them kept decreasing with alveolar bone reduction, but the ratio to length of the averaged root embedded in the alveolar bone was stable at around $33\%$ regardless of that. 3. Under unreduced condition, the center of resistance during initial displacement of mandibular 6 anterior teeth was located at the Point of about $43\%$ apically from CEJ of the averaged tooth of them and this ratio kept increasing to about $54\%$ with root reduction. But the distance from CEJ to the center of resistance decreased from around 5.3mm to around 3.3mm, that is to say, the center of resistance kept shifting toward CEJ with the shortening of root length. 4. A unit reduction of alveolar bone had greater effects on the change of the centers of resistance than that of root did during initial Phase of each reduction. But both of them had similar effects at the middle region of whole length of the averaged root.

• Korea-Australia Rheology Journal
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• v.17 no.1
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• pp.9-13
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• 2005

The aggregation of red blood cells (RBCs) is a major determinant of blood flow resistance passing through various veins. Available techniques for measuring RBC aggregation often require pretreating and washing after each measurement, which is not optimal for day-to-day clinical use. A laser reflection technique has been combined with a vibration-aided disaggregation mechanism, which shows significant advances in aggregometer design, operation and data analysis. The essential features of this design are in its simplicity and a disposable element that is in contact with the blood sample. Using extremely small quantities of blood, the RBCs subjected to vibrations can be quickly and completely disaggregated. This is followed by measuring the backscattered light intensity. The measurements with the present sensor were compared with those of a commercial aggregometer and a strong correlation was found between them. The newly-developed optical aggregometer can measure the RBC aggregability difference between young and old cell suspension with ease and accuracy.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.124-128
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• 1999

We report microwave properties of high-T$_c$ superconducting (HTS) microstrip antennas without impedance matching circuits, where the impedance mismatching is obvious under the critical temperature (T$_c$). The superconducting thin films used in this report were YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on MgO substrates produced by pulse laser deposition (PLD) technique. At around T$_c$, 86 K the reflection coefficient rapidly drops, and the standing wave ratio (SWR) becomes almost unity, and the characteristic impedance based on the Smith chart is nearly 50 ${\Omega}$. The reflection coefficient and the SWR of the HTS microstrip antenna were - 62.52 dB and 1.0015, respectively, at the resonant frequency of 11.812 CHz at 86 K.

• Journal of Internet Computing and Services
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• v.9 no.3
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• pp.69-77
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• 2008

An algorithm for tracking the trace of structured light is proposed to obtain depth information accurately. The technique is based on the fact that the pixel location of light in an image has a unique association with the object depth. However, sometimes the projected light is dim or invisible due to the absorption and reflection on the surface of the object. A dynamic programming approach is proposed to solve such a problem. In this paper, necessary mathematics for implementing the algorithm is presented and the projected laser light is tracked utilizing a dynamic programming technique. Advantage is that the trace remains integrity while many parts of the laser beam are dim or invisible. Experimental results as well as the 3-D restoration are reported.