• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.581-584
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• 2000

Generally, it is known that many partial discharges are occurred in one voltage cycle. In this case, it is not easy to distinguish between ultrasonic signals caused by the partial discharge. We describes a pattern of the ultrasonic signal by the partial discharge in transformer. The test setup for ultrasonic signal measurement was to simulate a internal partial discharge by using a needle to plane electrodes. We compared the number of partial discharge and ultrasonic signal in one voltage cycle. The results showed that it was possible to distinguish between ultrasonic signals by analysing partial discharge detection method and ultrasonic signal on time domain.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.1
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• pp.33-38
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• 2003

This paper describes control principles of the piezoelectric ultrasonic motor which is operated by the ultrasonic vibration generated by the piezoelectric element. The piezoelectric ultrasonic motor has excellent characteristics such as compact size, noiseless motion, low speed, high torque and controllability, and has been recently applied for the practical utilization in industrial, consumer, medical and automotive fields. In this paper, the design of two-phase push-pull inverter for driving the piezoelectric ultrasonic motor is described, and a new control method of automatic resonant frequency tracking using PLL(Phase-Locked Loop) technique is mainly presented. the experimental results by this inverter system for driving the piezoelectric ultrasonic motor are illustrated herein. The inverter system with PLL technique improved the speed stability of the piezoelectric ultrasonic motor.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.670-676
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• 2014

The objective of this research is to utilize the ultrasonic method to analyze the property of partial discharge (PD) which is generated by the winding of the insulation stator in the generator. Therefore, a PD measurement system is built based on ultrasonic and virtual instruments. Three types of PD models (internal PD model, surface PD model and slot PD model) have been constructed. With the analysis of these experimental results, this research has identified the ultrasonic signals of the discharges which were produced by three types of PD models. This analysis shows the different features among these PD types. Both the time domain and frequency domain of the ultrasonic signals are obviously different. In addition, an experiment based on a large rotating machine has been done to analyze ultrasonic noises. The result indicates that the ultrasonic noises can be wiped off by the filters and algorithms. The application of this system is convenient for the detection of early signs of insulation failure, which is an effective method for diagnosis of insulation faults.

• Journal of the Korean Wood Science and Technology
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• v.25 no.3
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• pp.8-15
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• 1997

The ultrasonic velocity and dynamic MOE of acetylated bamboos were investigated using PUNDIT, a transit time measuring device for longitudinal ultrasonic propagation. Bamboo specimens were boiled in acetic anhydride for 2, 4 and 6 hours, and the maximum average WPG (Weight Percentage Gain) of 19% was obtained at 6 hours. The volumes of acetylated bamboos increase with boiling time and WPG, while as WPG increases their oven-dry densities generally increase with a concave around 5% WPG. This oven-dry density pattern likely influences the trends of ultrasonic velocity and dynamic MOE. which generally decrease with a convex around 5% WPG. It is postulated that during boiling extractives in a bamboo move and aggregate at its surfaces transiently, resulting in the increase of ultrasonic velocity and dynamic MOE. To explain the fact that ultrasonic velocity varies with WPG a simple model was proposed and some ultrasonic properties of a transmitted wave were examined.

• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1167-1174
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• 2022

Cast austenitic stainless steels (CASSs) are widely used as structural materials in the nuclear industry. The main drawback of CASSs is the reduction in fracture toughness due to long-term exposure to operating environment. Even though ultrasonic non-destructive testing has been conducted in major nuclear components and pipes, the detection of cracks is difficult due to the scattering and attenuation of ultrasonic waves by the coarse grains and the inhomogeneity of CASS materials. In this study, the ultrasonic signals measured in thermally aged CASS were discriminated for the first time with the simple ultrasonic technique (UT) and machine learning (ML) models. Several different ML models, specifically the K-nearest neighbors (KNN), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP) models, were used to classify the ultrasonic signals as thermal aging condition of CASS specimens. We identified that the ML models can predict the category of ultrasonic signals effectively according to the aging condition.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.5
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• pp.239-245
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• 2022

The purpose of this study is to evaluate the degree of microstructural change of materials using ultrasonic nonlinear parameters. For microstructure change, isothermal heat-treated ferritic 2.25Cr steel and low-cycle fatigue-damage copper alloy were prepared. The variation in ultrasonic nonlinearity was analyzed and evaluated through changes in hardness, ductile-brittle transition temperature, electron microscopy, and X-ray diffraction tests. Ultrasonic nonlinearity of 2.25Cr steel increased rapidly during the first 1,000 hours of deterioration and then gradually increased thereafter. The variation in non-linear parameters was shown to be coarsening of carbides and an increase in the volume fraction of stable M6C carbides during heat treatment. Due to the low-cycle fatigue deformation of oxygen-free copper, the dislocation that causes lattice deformation developed in the material, distorting the propagating ultrasonic waves, and causing an increase in the ultrasonic nonlinear parameters.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.4
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• pp.80-91
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• 2002

An on-line ultrasonic detector was developed to continuously monitor the ultrasonic signal due to partial discharge in transformer in service. The on-line ultrasonic detector has a band-pass filter designed to measure only the frequencies from 50 to 300[㎑] of ultrasonic signal, to remove electrical and mechanical noises from outside of the transformer, and tlle ultrasonic sensor contains a pre-amplifier with 60[dB] gain. The ultrasonic signal discrimination algorithm which discriminates the ultrasonic signal duration was developed to remove the ultrasonic signal due to OLTC operation having similar characteristics to those due to partial discharge. The reliability of the on-line ultrasonic detector developed in this study was convinced of measurement the ultrasonic signals from the model. transformer in laboratory and transformer in service.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.1
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• pp.63-73
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• 2010

This paper presents the optimal design method of an overlapped ultrasonic sensor ring for reduced positional uncertainty, and its application to the obstacle detection with improved resolution. Basically, it is assumed that a set of ultrasonic sensors are installed to form a circle at regular intervals with their beams overlapped. First, exploiting the overlapped beam pattern, the positional uncertainty inherent to an ultrasonic sensor is shown to be significantly reduced. Second, for an ideal ultrasonic sensor ring of zero radius, the effective beam width is defined to represent the positional uncertainty, and the optimal number of ultrasonic sensors required for minimal effective beam width is obtained. Third, for an actual ultrasonic sensor ring of nonzero radius, the design index is defined to represent the degree of positional uncertainty, and an optimal design of an overlapped ultrasonic sensor ring consisting of commercial ultrasonic sensors with low directivity is given. Fourth, given measured distances from ultrasonic sensors, the geometric method is described to compute the obstacle position with reference to the center of a mobile robot. Finally, through experiments using our overlapped ultrasonic sensor ring prototype, the validity and performance of the proposed method is demonstrated.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.3
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• pp.504-516
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• 1997

Ultrasonic instruments transfer electrical energy to mechanical energy resulting in vibration used for various dental treatments. If we could know the effect of ultrasonic instruments on the dental cements within the cast crown, we could take care when conducting periodontal surgery and when using the ultrasonic instrument to remove cast crown, it would be much more convenient. The purpose of this study was to compare the bond strength of several dental cements according to ultrasonic instrumentation time. In this study 4 types of cements were used to cement the specimens. they were treated with ultrasonic instrumentation for 0-5 minutes and the change in bond strength were statistically compared. The results were as followed. 1. The tensile bond strength of zinc phosphate cement decreased according to the increase in time of ultrasonic instrument and showed significant difference between 0 minutes and the others and between 1 minute and 2,3,4,5 minutes (p<0.05). 2. The tensile bond strength of polycarboxylate cement decreased according to the increase in time of ultrasonic instrument and showed significant difference between 5 minutes and the others and between 4 minutes and 0 minutes (p<0.05). 3. The tensile bond strength of zinc phosphate cement decreased according to the increase in time of ultrasonic instrument and showed significant difference between 5 minutes and the others (p<0.05). 4. The tensile strength of resin cements showed no statistically differences according to the ultrasonic instrumentation time. In conclusion, it is considered that zinc phosphate cements is most affected by ultrasonic instrumentations and resin cement is the least affected. When using ultrasonic instruments the result avove should be used as an index.

• Computers and Concrete
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• v.6 no.3
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• pp.225-234
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• 2009

Dredged silt from reservoirs in southern Taiwan was sintered to make lightweight aggregates (LWA), which were then used to produce lightweight aggregate concrete (LWAC).This study aimed to assess the compressive strength and homogeneity of LWAC using ultrasonic-echo sensing. Concrete specimens were prepared using aggregates of four different particle density, namely 800, 1100, 1300 and 2650 kg/$m^3$. The LWAC specimens were cylindrical and a square wall with core specimens drilled. Besides compressive strength test, ultrasonic-echo sensing was employed to examine the ultrasonic pulse velocity and homogeneity of the wall specimens and to explore the relationship between compressive strength and ultrasonic pulse velocity. Results show that LWA, due to its lower relative density, causes bloating, thus resulting in uneven distribution of aggregates and poor homogeneity. LWAC mixtures using LWA of particle density 1300 kg/$m^3$ show the most even distribution of aggregates and hence best homogeneity as well as highest compressive strength of 63.5 MPa. In addition, measurements obtained using ultrasonic-echo sensing and traditional ultrasonic method show little difference, supporting that ultrasonic-echo sensing can indeed perform non-destructive, fast and accurate assessment of LWAC homogeneity.