• Journal of Industrial Technology
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• v.25 no.B
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• pp.115-120
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• 2005

Impact seismic wave method is a method for non-destructive testing of concrete structure using of stress wave which is propagate and reflected from internal flaws within concrete structure and external surface. In this study, we performed frequency domain method using impact seismic wave test for safety diagnosis of civil engineering structure. And reflection method which is used for one-dimensional target such as tunnel lining and transmission method are compared with each other.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.411-416
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• 2006

The critical subject of transverse crack detection in a rail head is treated in this paper. Conventional bulk wave ultrasonic techniques oftenfail because of shelling and other surface imperfections that shield the defects that lie below the shelling. A guided wave inspection technique is introduced here that can send ultrasonic energy along the rail under the shelling with a capability of finding the deleterious transverse crack defects. Dispersion curves are generated via a semi analytical finite element technique along with a hybrid guided wave finite element technique to explore the most suitable modes and frequencies for finding these defects. Sensor design and experimental feasibility experiments are also reported.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.498-501
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• 2006

When an object or objects, rigid or flexible, presents in incident sound field, the sound wave is scattered. This, we call, is scattered sound field. It, of course, depends on the amplitude and the direction of the incident sound field as well as the geometry and the surface impedance of the scatterer(object). This paper addresses the way to measure scattered sound field by using arbitrary incident sound wave. This means that the method can decompose the scattered field from measured sound field with respect to any magnitudes and directions of incident plane-waves.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1110-1116
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• 2010

Void ratios are one of the key parameters for exact calculation of settlement of soft groundse. In the study, shear wave velocities of a soft ground were used to measure the field void ratio using bender elements sensors. The bender-element probes were installed in situ at the depths of 3, 5 and 8m on a pre-loading site near Incheon, Korea. During 90 days after installation, the changes of shear wave velocity and ground surface settlement were measured. The field void ratio was estimated from measured shear wave velocities. The void ratio estimated by the shear wave velocity measured by bender elements agrees well with the measured values in the field.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.628-629
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• 2009

A variety of technologies have already been developed to capture energy from the ocean waves, this one is simple to construct. Rather then looking at the surface waves, the technique used lets the waters current beneath the waves directly drive the rotors. The novel ocean wave energy convertor consists of savonius rotor which is mounted in the ocillating water column (OWC) chamber. This study investigates the performance of a 3 blade and 5 bladed savonius rotor under same wave condition using commercial CFD code. Initially the performance analysis of savonius type turbine have been carried out with conventional three bladed curved rotors. From the experieneces of the simulations, 5 bladed savonius rotor have been developed and studied. Performace caracteristics of the 5 bladed savonius rotor has been evaluated and the results obgtained are comopared with the conventional three bladed curved rotors.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.261-266
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• 2003

The presence of ultrasonic wave in the caustic etching process enhances the etching rate and results in finer and more homogeneous textured structure of the crystalline silicon surface. The silicon solar cell textured in the caustic solution at $60^{\circ}C$ with ultrasonic wave gives higher cell performance than the cell textured at $70^{\circ}C$ without ultrasonic wave. This result indicates a strong possibility of lowering the production cost of the silicon solar cell through saving the thermal budget or expensive chemical normally employed in the texturisation of the crystalline silicon.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.681-684
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• 2003

Piezoelectric motors have been successfully developed for various applications like autofocus drives in camera lenses and handling equipment for high-accuracy positioning. In this paper, the travelling-wave motor which used in the camera lense, using bending vibration of a ring was studied. The basic structure of the motor is same but we suggested a few parameters for considering their design. The parameter is different from sine and cosine region of the voltage of the ceramic surface, displacement according to the wave number difference, and the phase difference. Same size of ceramics and aluminium ring were used for the stator. As a result, the displacement is dependent on the wave number.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1101-1106
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• 2004

There are many difficulties to get the scattered field generated by obstacle which has arbitrary shape or irregular surface impedance by using analytic solution or numerical methods. In this study, we propose a method of which makes acoustic scattering holography that can predict the far-field scattered field based on nearfield measurements. This method provides the scattered fields of each wave-number components of incident fields. We express the relationship of wave-number components between incident fields and scattered fields using scattering matrix which is transfer matrix of wave-number components. Lastly, we prove the relation between wave-number components of incident and scattered field by experiments. The errors which are caused by measurements and decomposition methods are also analyzed.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.6
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• pp.398-406
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• 2015

This paper explored the results of experimental investigation on carbon fiber reinforced polymer (CFRP) composite sample with thermal wave technique. The thermal wave technique combines the advantages of both conventional thermal wave measurement and thermography using a commercial Infrared camera. The sample comprises the artificial inclusions of foreign material to simulate defects of different shape and size at different depths. Lock-in thermography is employed for the detection of defects. The temperature field of the front surface of sample was observed and analysed at several excitation frequencies ranging from 0.562 Hz down to 0.032 Hz. Four-point methodology was applied to extract the amplitude and phase of thermal wave's harmonic component. The phase images are analyzed to find qualitative and quantitative information about the defects.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.1
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• pp.30-35
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• 2004

We have carried out a basic experiment in order to develope a super high-resolution optical microscope which transcend the limitation of diffraction and the wavelength of lightwave. The image of this scope is composed by measuring the evanescent wave which is localized on the surface of the testing materials. A detecting probe was fabricated with a single mode optical fiber to be sharpened by the chemical etching, and drived by PZT. The standing wave of $0.33\mu\textrm{m}$ wavelength evanescent wave which was generated from the $0.78\mu\textrm{m}$-wavelength semiconductor laser was detected by the $0.5\mu\textrm{m}$-thickness optical fiber probe.