• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1591-1594
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• 1987

The Scanning Acoustic Microscope(SAM) is an image device which can display the small opaque material or the interior of solid. This paper showed the design of the acoustic lens which is an important factor of the Scanning Acoustic Microscope, and analyzed the performance of the acoustic lens. Finally, I experimented the image processing of the interior of solid through the Scanning Acoustic Microscope and the change of the acoustic image (resolution,contrast) by the change of F/number.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.555-556
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• 2014

In this paper, topology optimization of two-dimensional acoustic lenses is presented by using the phase field method. The objective of the optimization is to maximize the acoustic pressure at a specified domain inside the acoustic domain for a given frequency, and the constraint is imposed on the amount of the material of the acoustic lens. Topology optimization of two-dimensional acoustic lenses are obtained as the steady state of the phase transition described by the Allen-Cahn equation. The Helmholtz equation modeling the wave propagation is solved by using a finite element method. The effectiveness of the proposed method is verified by applying it for several two-dimensional acoustic lens system design problems.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.3
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• pp.116-123
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• 2023

A high intensity focuses ultrasound (HIFU) is one of the emerging technologies in the biomedical field. The piezoelectric HIFU transducer is a device that utilizes the thermal energy generated by high ultrasound energy. Recently an operating frequency of the HIFU transducer is to expand above a 7 MHz. In this study, the acoustic pressures and temperature distributions in the tissue that generated by the HIFU transducer at 10 MHz were calculated with the finite element method. In addition, the pressure focusing characteristics of the device were analyzed. The geometrical variables are the piezomaterial thickness, lens shape, water height, and film thickness. The results shown that the acoustic pressure increased and saturated gradually when the height/radius (H_L/R_L) ratio of the lens increased. Moreover, the focal area was gradually decreases with H_L/R_L ratio of the lens. In case of the optimized HIFU transducer, the maximum pressure and temperature were analyzed about 19 MPa and 65℃ respectively. And the -3 dB focused distances in the axial and lateral direction are around 2.3 mm and 0.23 mm respectively.

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.33-41
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• 2009

A multilevel acoustic Fresnel lens (MAFL) for the ultrasonic imaging transducer of which center frequency is approximately 5.MHz was newly designed and fabricated. The phase level of the lens was 64, and the focal length and the aperture width were 30.mm and 11.mm, respectively. The characteristics of impulse response, acoustic field and imaging performance of the transducer attached the lens were compared with the transducer attached a conventional refraction type acoustic lens (RAL). The results show that the center frequency, the loop sensitivity, and the focal depth of the MAFL transducer were higher or larger than those of the RAL transducer by approximately 0.2.MHz, 1.4.dB, and 2.mm, respectively. Consequently, it was shown that the brighter acoustic images with higher lateral resolution and the increased imaging performance for deep targets can be obtained by using the MAFL transducer.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.18-24
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• 2011

A multi-channel seismic reflection (MCS) survey was conducted in 2009 to explore the deep crustal structure of the Pacific Plate south of Hokkaido. The survey line happened to traverse a 250-km-wide Warm Core Ring (WCR), a current eddy that had been generated by the Kuroshio Extension. We attempted to use these MCS data to delineate the WCR fine structure. The survey line consists of two profiles: one with a shot interval of 200m and the other with a shot interval of 50 m. Records from the denser shot point line show much higher background noise than the records from the sparser shot point line. We identified the origin of this noise as acoustic reverberations between the sea surface, seafloor and subsurface discontinuities, from previous shots. Results showed that a prestack migration technique could enhance the signal buried in this background noise efficiently, if the sound speed information acquired from concurrent temperature measurements is available. The WCR is acoustically an assemblage of concave reflectors dipping inward, with steeper slopes (${\sim}2^{\circ}$) on th ocean side and gentler slopes (${\sim}1^{\circ}$) on the coastal side. Within the WCR, we recognised a 30-km-wide lens-shaped structure with reflectors on the perimeter.

• The Journal of the Korea Contents Association
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• v.10 no.6
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• pp.236-248
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• 2010

Through this thesis, I analyzed Coen brothers's directing style centering around Crime movies: Blood simple, Barton Fink, Fargo, The man who wasn't thers, No country for old man. About directing style of Coen brothers, plot is an epic depiction, habitual use of narration, refusal of happy ending. They concern subject matters about human original nature and tragedy by greed. And as motifs, they often use misunderstanding, crossing over, chase. Also they likes characters of ordinary people who is destroyed by greed. How about their technical style? They usually use steady-cam and wide lens in camera, and in his early crime movies he used expressionistic lights, but after that they usually used realistic natural lights. About sound, they likes more sound effects than music. Also they directed realistic acting and emphasized actor's personality. Coen brothers has been directed many crime movies and comedy films. But their unique directing style was particularly outstanding in the crime movies

• The Journal of the Korea Contents Association
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• v.12 no.5
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• pp.81-90
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• 2012

Since the Canon EOS 5D Mark II with which the Full HD video shooting is possible was launched in 2008, the utilization of the DSLR cameras has been increasing in the video production field. In this thesis, the shortages and advantages of the video functions that the 5D Mark II cameras have will be analysed and they will be compared with the RED cameras that are most widely used in the video production field today. Through this, the utilization of the DSLR camera in the film production field will be investigated. The DSLR camera has the advantage of having good clear picture since it uses the image sensor of big size, and of being able to utilize the various lenses of good quality, and is small in size and light in weight compared to the conventional HD cameras. Although, there are some limitations that there are parts to be improved such as the sound recording problems and development of various additional equipments, the excellent usage that the DLSR cameras have is presenting a new possibility for the film production.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.370-376
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• 2016

Corrosion on the surface of a structure can generate cracks or cause walls to thin. This can lead to fracturing, which can eventually lead to fatalities and property loss. In an effort to prevent this, laser imaging technology has been used over the last ten years to detect thin-plate structure, or relatively thin piping. The most common laser imaging was used to develop a new technology for inspecting and imaging a desired area in order to scan various structures for thin-plate structure and thin piping. However, this method builds images by measuring waves reflected from defects, and subsequently has a considerable time delay of a few milliseconds at each scanning point. In addition, the complexity of the system is high, due to additional required components, such as laser-focusing parts. This paper proposes a laser imaging method with an increased scanning speed, based on excitation and the measurement of standing waves in structures. The wavenumber of standing waves changes at sections with a geometrical discontinuity, such as thickness. Therefore, it is possible to detect defects in a structure by generating standing waves with a single frequency and scanning the waves at each point by with the laser scanning system. The proposed technique is demonstrated on a wall-thinned plate with a linear thickness variation.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.74-87
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• 2014

Analysis of multi-channel seismic reflection profiles collected from the Ulleung Basin reveals that the Quaternary sequence consists of four stratigraphic units separated by erosional unconformities. Individual stratigraphic unit includes eighteen mass transport deposits which are variable in geometric characteristics and spatial distribution. Each mass transport deposit on the seismic profile is acoustically characterized by chaotic or transparent seismic facies, and shows wedge or lens-shaped external geometry. The mass transport deposits, which comprise a succession of stacked wedges, mainly occur on the southern slope, and their thickness gradually decreases toward the basin plain. The time structure map of erosional unconformities shows that a tectonic-induced structural high and troughs toward the northwest and northeast are developed at the central part of the basin. Based on the isochron map, the mass transport deposits, originated from southern part of the study area, transported to the basin plain and can be divided into two groups by the structural high. Consequently, the mass transport deposits within the Quaternary sequence in the Ulleung Basin are largely controlled by the large amounts of sediment supply, dissociation of gas hydrate during the lowstands, and central structural high.

• Economic and Environmental Geology
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• v.38 no.6 s.175
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• pp.633-642
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• 2005

We present the sedimentary sequence and distribution pattern of the late Holocene muddy deposits in the northern East China Sea shelf using the high-resolution 'Chirp' profiles. The seismic sedimentary sequence overlying acoustic basement (basal reflector-B) can be divided into two depositional units (Unit 1 and 2) bounded by erosional bounding surface (mid reflector-M). The lower Unit 1 above basal reflector-H is characterized by the acoustically parallel to subparallel reflections and channel-fill facies. The upper Unit 2, up to 7 m in thickness, shows seismically semi-transparent seismic facies and lenticular body form. On the base of sequence stratigraphic concept, these two sediment units have developed during transgression and highstand period, respectively, since the last sea-level lowstand. The transgressive systems tract (Unit 1) lie directly on the sequence boundary (reflector B) that have farmed during the last glacial maximum. The transgressive systems tract in this study consists mostly of complex of delta, fluvial, and tidal deposits within the incised valley estuary system. The maximum flooding surface (reflector M) corresponding to the top surface of transgressive systems tract is obviously characterized by erosional depression. The highstand systems tract (Unit 2) above maximum flooding surface is made up of the mud patch filled with the erosional depression. The high-stand mud deposits showing a circle shape just like a typhoon symbol locates about 140 km off the south of Cheju Island with water depth of $60\~90m$. Coverage area and total sediment volume of the mud deposits are about $3,200km^2$ and $10.7\times10^9\;m^3$, respectively. The origin of the mud patch is interpreted as a result of accumulating suspended sediments derived from the paleo-Yellow and/or Yangtze Rivers. The circular distribution pattern of the mud patch appears to be largely controlled by the presence of cyclonic eddy in the northern East China Sea.