• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.696-700
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• 2007

In case of dome-typed gymnastics training floor, since its form takes shape of the focus of sound, in the occasion when the finishing-material was used with the sandwich panel that prominent in reflexibility, and because the reverberation of sound in indoor is too loud, a smooth practice and teaching is very difficult. As this indoor gymnastics training floor, standing at its character, is required simultaneously the idea communication between the player and the coach, and the acoustic capability regarding to the clearness of music, besides the sport activity, the method to minimize the acoustic defect should be urgently contrived from the stages of design and beginning of construction. On this viewpoint, after investigation on the confidence of the surveyed value and the estimated value using acoustic simulation, and use of the changed finish-material, this thesis intends to design the dome-typed gymnastics training floor that secured the optimized acoustic condition. It is also considered that such result of the study could be utilized as the useful data that enables to improve the retrenchment effect of the construction cost as well as the acoustic performance, by means of the prediction control on the acoustic problem from the stage of design, for the occasion when the similar indoor sport gymnasium is planning to build for the near future.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.1
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• pp.53-60
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• 2010

This paper dealt with the acoustic detection of partial discharge (PD) in insulation oil for insulation diagnostics of oil immersed transformers. Electrode systems such as needle to plane, plane to plane, and floating were fabricated to simulate some defects in transformers. A wide band acoustic emission(AE) sensor with the frequency ranges of 100 kHz~1 MHz and a narrow band AE sensor with the resonant frequency of 140 kHz were used in the experiment. Also, a decoupler and an amplifier were designed to detect and amplify the acoustic signal only. The decoupler separates acoustic signal from DC source without any distortion, and the amplifier has the gain of 40 dB in frequency ranges of 11 kHz~4 MHz. In the experiment, frequency components and propagation characteristics of acoustic signal were analyzed, and an algorithm of positioning of PD occurrence by the time difference of arrival was proposed. From the results, the frequency components of the acoustic signal exist from 50 kHz to 200 kHz and the positioning error of PD calculated by three AE sensors was within 1%.

• Applied Microscopy
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• v.50
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• pp.25.1-25.11
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• 2020

Scanning acoustic microscopy (SAM) or Acoustic Micro Imaging (AMI) is a powerful, non-destructive technique that can detect hidden defects in elastic and biological samples as well as non-transparent hard materials. By monitoring the internal features of a sample in three-dimensional integration, this technique can efficiently find physical defects such as cracks, voids, and delamination with high sensitivity. In recent years, advanced techniques such as ultrasound impedance microscopy, ultrasound speed microscopy, and scanning acoustic gigahertz microscopy have been developed for applications in industries and in the medical field to provide additional information on the internal stress, viscoelastic, and anisotropic, or nonlinear properties. X-ray, magnetic resonance, and infrared techniques are the other competitive and widely used methods. However, they have their own advantages and limitations owing to their inherent properties such as different light sources and sensors. This paper provides an overview of the principle of SAM and presents a few results to demonstrate the applications of modern acoustic imaging technology. A variety of inspection modes, such as vertical, horizontal, and diagonal cross-sections have been presented by employing the focus pathway and image reconstruction algorithm. Images have been reconstructed from the reflected echoes resulting from the change in the acoustic impedance at the interface of the material layers or defects. The results described in this paper indicate that the novel acoustic technology can expand the scope of SAM as a versatile diagnostic tool requiring less time and having a high efficiency.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.40-52
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• 1998

Among the non-traditional machining methods, Abrasive waterjet machining process shows big promise in drilling difficult-to-machine materials due to its numerous advantages such as absence of heat affect zone and thermal distortion. Acoustic emission signal technique is used to understand about material removal mechanisms during abrasive waterjet drilling process. More information about the drilling process is derived through frequency decomposition of auto regressive moving average modeling representing acoustic emission signals.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.144-146
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• 1992

Surface acoustic wave(SAW) oscillator offers many attractive features for application to vapor sensors. The perturbation of SAW velocity by the hexafluoropropence plasma polymer thin film has been studied for relative humidity sensing. adsorption of moisture produces rapid aid changes in the properties of the film, resulting in a change in the velocity of surface acoustic waves and, hence, in the frequency of one SAW oscillator. The device used in our experiments have 55 MHZ SAW oscillator fabricated on a LiNbO substrate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.283-286
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• 2000

In this study, the acoustic transducer of a thin circular disc-type with PZT/Metal was manufactured. The piezoelectric transducer with 200kHz resonance frequency was designed by considering the sharp directivity and the sound pressure. The dielectric and piezoelectric properties of 0.5 weight percent $MnO_2$ and NiO doped $0.1Pb(Mg_{1/3}Nb_{2/3})O_3-0.45PbTiO_3-0.42PbZrO_3$ ceramics were investigated aiming at acoustic transducer applications. Also, the acoustic characteristics of a thin circular disc-type with metal-piezoceramics have been Investigated.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1044-1049
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• 2007

The construction of concrete slab track system is increased because the system has advantages which are maintenance free and so on, the other side, the system has weak points such as increase of the cost of the early stage construction and noise levels. The increment of noise is due to the reflection of generated noise on the slab tracks. Therefore the acoustic-absorptive materials are considered to reduce noise level. It has been made clear that acoustic-absorptive materials are effective for reducing the wheel/rail noise on slab tracks. The important performance of the acoustic-absorptive material is absorption rates and absorption rates are verified for the considered absorber elements using acoustic duct method. In addition, the required provisons for installing acoustic-absorptive block on slab tracks are considered.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.770-773
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• 2004

The transmission loss coefficient is very important acoustic property in parallel with absorption and acoustic impedance categorizing the acoustical materials, which can control the acoustical problems. At the same time, the transmission loss coefficient is a key parameter to choose the optimum material for the analysis of acoustical characteristics of material using SEA(Statistical Energy Analysis). In this paper, the acoustic transmission loss measurement system using 4-microphone TL tube is applied to the exhaust system, which is one of the most important acoustic control parameters in a car, based on the idea calculating the full transfer matrix. The theoretical background and measurement system are introduced, and finally the measurement results are verified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.35-38
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• 2003

In this paper, we investigated the electric and acoustic properties of piezoelectric composites, which were fabricated using polymer and piezoelectric ceramics, when the volume fraction of PZT varies. Practically, the shrinkage rate of polymer is an important factor in ultrasonic transducer fabrication. When 10 wt% filler A was added into polymer(Epofix), the lowest shrinkage was resulted. The electromechanical coupling factor($k_t$) of the fabricated piezoelectric composites showed its highest when the volume fraction PZT was 0.6. It decreased if the volume fraction was higher than the value. The relative permittivity and acoustic impedance of piezoelectric composites decreased linearly when PZT volume fraction was decreased. The lowest acoustic impedance was 3.2 when the volume fraction of PZT was 0.2.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.3
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• pp.118-123
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• 2019

The aim of this study investigates the feasibility of scanning acoustic microscope (SAM) with high frequency transducer for material degradation. The test specimen was prepared by artificial heat treatment of Co-base superalloy. The high frequency 200 MHz acoustic lens was used to generate the leaky surface acoustic wave (LSAW) on the test specimens. The matrix precipitates coarsened with thermal aging time, and then grow up to several tens of micrometers. The velocity of LSAW decreased with increasing aging time. Also, it has a good correlation between LSAW and hardness. Consequently, V(z) curve methods of SAM using high frequency transducer is useful tool to evaluate the heat treatment effects on microstructure.