• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.53-59
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• 2016

Ultrasonic nonlinear evaluation is generally utilized for detection of not only defects but also microdamage such as corrosion and plastic deformation. Nonlinearity is determined by the amplitude ratio of primary wave second harmonic wave, and the results of its comparison are used for evaluation. Owing to the experimental features, the experimental nonlinearity result contains system nonlinearity and material nonlinearity. System nonlinearity is that which is unwanted by the user; hence, it acts as an error and interrupts analysis. In this study, a bulk wave mixing technique is implemented in order to minimize the system nonlinearity and obtain the reliable analysis results. The biggest advantage of this technique is that experimental nonlinearity contains less system nonlinearity than that for the conventional nonlinear ultrasonic technique. Theoretical and experimental verifications are performed in this study. By comparing the results of the bulk wave mixing technique with those of the conventional technique, the strengths, weaknesses, and application validity of the bulk wave mixing technique are determined.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.11
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• pp.919-925
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• 2016

In this study, the Lamb wave mixing technique, which is basised on advanced research on the nonlinear bulk wave mixing technique, is applied for corrosion detection. To demonstrate the validity of the Lamb wave mixing technique, an experiment was performed with normal and corroded specimens. Comparison group in an experimentation are selected to mode and frequency with dominant in-plane displacement and out-of-plane displacement of Lamb waves. The results showed that the Lamb wave mixing technique can monitor corrosion defects, and it has a trend similar to that of the conventional Lamb wave technique. It was confirmed that the dominant displacement and mode matching the theory were generated. Flaw detectability is determined depending on displacement ratio instead of using the measurement method and mode selection.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.7
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• pp.217-225
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• 2000

Scanning Acoustic Microscope (SAM) is used as an important nondestructive test tool in semiconductor reliability evaluation and failure analysis. However, inspections of chip attach adhesive interface fer thin chip has proven difficulty as the reflected signals from the chip top and bottom are superimposed. In this paper, in order to overcome this difficulty, a new signal processing method based on the deconvolution technique combined with the wavelet transform is proposed. The wavelet transform complements a disability of deconvolution technique of which performance largely decreases when the waveform of target signal is not identical to that of reference signal. Performances of the proposed method are demonstrated by through computer simulations using model signal and experiments for the fabricated semiconductor samples, and satisfactory results are obtained.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.134-142
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• 2016

In this paper, a method synthesizing speech signal using the 40 kHz ultrasonic signals reflected from the articulatory muscles was introduced and performance was evaluated. When the ultrasound signals are radiated to articulating face, the Doppler effects caused by movements of lips, jaw, and chin observed. The signals that have different frequencies from that of the transmitted signals are found in the received signals. These ADS (Acoustic-Doppler Signals) were used for estimating of the speech parameters in this study. Prior to synthesizing speech signal, a quantitative correlation analysis between ADS and speech signals was carried out on each frequency bin. According to the results, the feasibility of the ADS-based speech synthesis was validated. ADS-to-speech transformation was achieved by the joint Gaussian mixture model-based conversion rules. The experimental results from the 5 subjects showed that filter bank energy and LPC (Linear Predictive Coefficient) cepstrum coefficients are the optimal features for ADS, and speech, respectively. In the subjective evaluation where synthesized speech signals were obtained using the excitation sources extracted from original speech signals, it was confirmed that the ADS-to-speech conversion method yielded 72.2 % average recognition rates.

• Journal of Energy Engineering
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• v.3 no.1
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• pp.54-61
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• 1994

계단형태의 고온발생장치로서, 고온의 흐름을 형성하고 난류유동이 없이 일정한 혼합기류를 만들 수 있는 2단격막구조 충격파관 장치를 이용하여, 혼합을 동반하지 않는 분무의 착화과정에 관한 실험을 수행하였다. 본 실험에서는 충격파관 속에 하향으로 설치된 초음파 분무기에 의해 자유낙하 상태에 있는 예혼합 분무주를 만들어서 반사충격파에 의해 순간적으로 단열압축시켜서 착화 현상을 관찰하였다. 고온영역과 저온영역에서 얻어진 활성화에너지는 큰 차이가 나며 본 연구에서 얻은 착화지연의 실험결과는 통상의 분무착화 실험인 전기로법, 급속압축기법, 고온기류속에 연료를 분사하는 방법과 다른 현상을 보였다. 그 대표적인 결과에 대한 예로는 착화지연에 대한 압력 의존성과 연료분사율의 영향이 일반적인 분무의 결과에 비해 적게 나타났다.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.138-149
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• 2000

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi mode conversion of guided wave scattering problems. Time dependent wave forms are obtained through the inverse Fourier transformation of the numerical solutions in the frequency domain. 3D BEM program development is underway to model more practical ultrasonic wave signals. Some encouraging numerical results have recently been obtained in comparison with the analytical solutions for wave propagation in a bar subjected to time harmonic longitudinal excitation. It is expected that the presented modeling techniques for elastic wave propagation and scattering can be applied to establish quantitative nondestructive evaluation techniques in various ways.

• Journal of Conservation Science
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• v.29 no.1
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• pp.35-45
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• 2013

The Clay Statues of Donggwanwangmyo Shrine (Treasure No. 142) are highly damaged physical weathering which are crack, exfoliation. Pigment of surface are discolored by chemical weathering like dust. The result of ultrasonic velocity measurement, low velocity zone was measured the lowest part of Woojanggun Statue. Deficiency condition of pigment layer was evaluated quantitatively through infrared Thermography. As a result, exfoliation part was detected at high temperature. Making techniques of the Clay statues were identified by gamma rays, infrared TV, SEM. All Clay Statues were founded on wood base and joints of wood were fixed using thin iron wires. After wood base was twisted a straw rope, it was made by clay. Clay was blended with rice straw to prevention of crack and exfoliation. The upper side of clay layer was coated with Hanji(Korean handmade paper) and cotton in order to isolate the pigment layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.9
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• pp.815-820
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• 2016

An elastic polymer (e.g., PDMS) blended with EFG particles is a promising conductive composite for fabricating soft sensors that can detect an object's deformation up to or more than 50%. Here, we develop large-strain, sprayable soft sensors using a mixture of PDMS and EFG particles, which are used as a host elastomer and electrically conductive particles, respectively. A solution for a conductive composite mixture is prepared by the microwave-assisted graphite exfoliation, followed by ultrasonication-induced fragmentation of the exfoliated graphite and ultrasonic blending of PDMS and EFG. Using the prepared solutions for composite and pure PDMS, 1-, 2-, and 3-axis soft sensors are fabricated by airbrush stencil technique where composite mixture and pure PDMS are materials for sensing and insulating layers, respectively. We characterize the soft strain sensors after investigating the effect of PDMS/EFG wt% on mechanical compliance and electrical conductance of the conductive composite.

• Journal of Korea Water Resources Association
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• v.55 no.1
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• pp.43-57
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• 2022

Advances in measurement techniques have reduced measurement costs and enhanced safety resulting in less uncertainty. For example, an acoustic doppler current profiler (ADCP) based suspended sediment concentration (SSC) measurement technique is being accepted as an alternative to the conventional data collection method. In Korean rivers, horizontal ADCPs (H-ADCPs) are mounted on the automatic discharge monitoring stations, where SSC can be measured using the backscatter of ADCPs. However, automatic discharge monitoring stations and sediment monitoring stations do not always coincide which hinders the application of the new techniques that are not feasible to some stations. This work presents and analyzes H-ADCP-SSC models for 9 discharge monitoring stations in Korean rivers. In application of the Gaussian mixture model (GMM) to sediment-related variables (catchment area, particle size distributions of suspended sediment and bed material, water discharge-sediment discharge curves) from 44 sediment monitoring stations, it is revealed that those characteristics can distinguish sediment monitoring stations regionally. Linking the two results, we propose a protocol determining the H-ADCP-SSC model where no H-ADCP-SSC model is available.

• Investigative Magnetic Resonance Imaging
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• v.5 no.1
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• pp.49-56
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• 2001

Purpose : To evaluate value of superparamagnetic iron oxide (SPIO) as a negative oral contrast agent in MR cholangiopancreatography (MRCP). Materials and methods : Forty-eight patients with suspected biliary tract or pancreatic diseases and six healthy volunteers were enrolled in this study. All MR images were obtained using a 1.5 T MR unit. MR-CP using fat-suppressed half-Fourier acquisition single-shot turbo spin echo (HASTE) and turbo spin echo (TSE) techniques were performed and reconstructed with maximal intensity projection (MIP). To determine the most optimal concentration of SPIO to obliterate the high signal intensity of water, a phantom experiment was conducted with various concentrations of SPIO-water mixture. Two radiologists evaluated pre- and postcontrast MRCPS. The contrast enhancement was assessed on the basis of loss of signal intensity in the stomach and duodenum. Results : In the phantom experiment, a significant increase of percentage of signal intensity loss (PSIL) occurred in concentration of 22.4 ugFe/ml (Feridex1 ml diluted with water 500 ml). Postcontrast MRCP showed an improved image quality compared with precontrast images. The rate of improvement in the diagnosis of diseases of the common bile duct and pancreatic duct was 25% (12/48). Conclusion : In patients with suspected biliary tract and pancreatic diseases, the SPIO is useful as a negative oral contrast agent for MRCP and provides an improvement of image quality.