• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.21-27
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• 2005

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.454-455
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• 2018

The impedance of an underwater acoustic transducers constituting a multi-channel array structure could be changed in real time by various transmission modes. A power amplifier for driving the transducers usually use a voltage control method, so the transducer and power amplifier may be damaged by over-power due to changeable load conditions. Therefore, the drive controller of the power amplifier should have the function of limiting the power. This paper propose the new voltage control method for limiting the driving power of transducers with variable impedance characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.317-320
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• 1999

In this study, the piezoelectric ceramics PZT powder was synthesized by Wet-Dry combination method. And the flexible 1-3-0 type composites were fabricated with piezoceramic PZT and Eccogel polymer matrix embedded 3rd phase. Dielectric constant of 1-3-0 type composites was lower than that of single phase PZT ceramics. Thickness mode coupling factor k/sub t/ which was comparable with single phase PZT ceramics and mechanical quality factor Qm were about 0.65 and 6, respectively. These composites are considered as a good candidates for broad-band type transducer applications. The acoustic impedance of 1-3-0 type composites was lower than that of single phase PZT ceramics. Therefore, these composites would be better used for hydrophone applications.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.4
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• pp.159-164
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• 2003

In this paper, a three-dimensional finite element method and construction of equivalent-circuit for a linear ultrasonic motor are presented. The validity of three-dimensional finite element routine in this paper is experimentally confirmed by analyzing impedance of a piezoelectric transducer. Using this confirmed finite element routine, impedance and vibration mode of a linear ultrasonic motor are calculated. Elliptical motion of contact point between vibrator and rail of the linear ultrasonic motor is shown for determination of contact points. By using the finite element method and analytic equations, characteristics of the linear ultrasonic motor, such as thrust force, speed, losses, powers and efficiency, are calculated. The results are confirmed by experiment. Finally, equivalent circuit parameters of the linear ultrasonic motor are obtained using the three-dimensional finite element method and analytic equations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.4
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• pp.481-489
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• 1993

The charge distribution is calculated to analyze the quasi-static impedance of periodic interdigital transducer taking into account the effect of infinite neighboring electrodes. The charge distribution can be represented by the element factor and array factor. The radiation conductance, susceptance and static capacitance of the input and output IDT's with arbitrary voltages are obtained by the charge distribution. The impedance of apodized IDT, is analyzed by multi-track model in which IDT is represented by the parallel connection of the uniform tracks. The calculated input and output impedances are in good agreement with the experimental results.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.764-769
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• 1994

The impedance of an electro-acoustic transducer can be controlled by motional feedback, and the noise in a duct can be reduced actively by adjusting the impedance using an additional sound. In this paper, two approaches for active noise control using motional feedback (MFB) loudspeaker are described. First configuration uses an external sensor to pickup of source directly. In this configuration, the adaptation of controller is necessary to compensate the change of transfer function from noise source to control poing. The second configuration uses a new adaptive algorithm specialized for peridic noise. Because this configuration does not require any reference input and the error sensor couples very tightly with control loudspeaker, this MFB system itself is independent of the duct condition. No microphone are required in both configurations, so that a more reliable and stable active control system can be realized under severe conditions such as high pressure, high temperature, dust, flow and so on.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.91-95
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• 1992

개영역(open boundary) 내의 변환기에 대한 음장 특성은 경계 조건이 좌표계와 정합되는 특수한 경우 헤름홀쯔 방정식풀이로 그렇지 않은 복잡한 형태의 음장에 대해서는 경계적분법이나 근사해법으로 얻어진다. 그러나 최근 이러한 문제들은 발달된 컴퓨터의 계산능력으로 유한요소법이나 경계요소법을 이용한 수치해법으로 해결되고 있다. 본 연구에서는 경계조건 변화에 따른 원통형 압전변환기의 방사임피던스 및 지향특성을 유한요소법 및 하이브리드형 무한요소법을 이용하여 구하고 기존의 해석적 결과와 비교하여 수중용 변환기 제작의 설계에 대한 기초자료를 제공하고자 한다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1997.06a
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• pp.53-56
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• 1997

Tonpilz 압전변환기에 관하여 유한요소법을 사용하여 공기중의 동특성 해석과 수중의 방사임피던스를 해석하였다. 공기중에서 트랜스듀서의 구조를 변화시키면서 입력 어드미턴스 특성과 진동모드를 해석하여 압전변환기를 모델링하였다. 음향 윈도우를 압전변환기 전면에 부착한 후 유한요소법(FEM)에 의하여 매질의 영향을 고려한 입력어드미턴스 특성을 해석하였으며, 또한 방사임피던스 계산 루틴을 추가하여 무한 배플의 경계조건하에서 방사 임피던스를 해석하였다. 공기중과 수중에서의 해석을 통하여 Tonpilz 압전변환기 단일 소자의 구조 변경 및 기계 부재의 추가등에 따라 변동하는 변환기의 특성 및 방사 임피던스를 해석하므로서 평면 배열형 음향 트랜스듀서의 설계에 필요한 파라메터를 구할 수있다.

• The Journal of Information Technology
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• v.8 no.1
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• pp.43-50
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• 2005

Quantitative analysis for distribution of penetrating ultrasound in vivo is very important to determine the treatment region and method. In this paper, we constructed a simplified 2-D femoral region model that consists of skin-fat-muscle-bone layered system, and simulated the pressure distribution in the model in case of applying ultrasound using Finite Element Method(FEM). The ultrasound used in the simulation was assumed to be pulse wave and the pressure distribution was analyzed during only one period of pulse wave. In order to find the penetration depth, amplitude of pressure and sphere that ultrasound reaches in the model, we performed the simulation with varying the applied frequency, transducer size and amplitude of transducer's output. The result showed that applied frequency is inversely proportional to the penetration depth and amplitude of pressure but the amplitude of transducer's output is proportional to the amplitude of pressure in the model. Also, the sphere that ultrasound reaches was widened and the amplitude of pressure became larger as the transducer size became larger. This results were similar to that obtained from the previous model consisting of fat-muscle-bone layered system, but we observed that the pressure of ultrasound is decreased due to the decrements of pressure by the absorption coefficient of skin and the interference that depends on the reflection of ultrasound caused by the difference of acoustic impedance of skin and fat. Finally, we can infer that the model proposed in this study is closer to the realistic model than the previous ones. It shows that the results obtained from this study can be useful in designing the ultrasound treatment instrument or in setting up the treatment plan.

• Smart Structures and Systems
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• v.11 no.4
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• pp.349-364
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• 2013

Recently, researchers in the field of structural health monitoring (SHM) have been rigorously striving to replace the conventional NDE techniques with the smart material based SHM techniques, employing smart materials such as piezoelectric materials. For instance, the electromechanical impedance (EMI) technique employing piezo-impedance (lead zirconate titanate, PZT) transducer is known for its sensitivity in detecting local damage. For practical applications, various external factors such as fluctuations of temperature and loading, affecting the effectiveness of the EMI technique ought to be understood and compensated. This paper aims at investigating the damage monitoring capability of EMI technique in the presence of axial stress with fixed boundary condition. A compensation technique using effective frequency shift (EFS) by cross-correlation analysis was incorporated to compensate the effect of loading and boundary stiffening. Experimental tests were conducted by inducing damages on lab-sized aluminium beams in the presence of tensile and compressive forces. Two types of damages, crack propagation and bolts loosening were simulated. With EFS for compensation, both cross-correlation coefficient (CC) index and reduction in peak frequency were found to be efficient in characterizing damages in the presence of varying axial loading.