• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.788-791
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• 2003

Optimal loudspeaker positions are important as much as the control algorithms and hardware performance in the active noise control system. This study is similar to the past researches on the optimal transducer locations but with a far field noise source having a plane wave characteristic and the noise coming through an opening such as a window in the enclosure. An optimization technique called simulated annealing algorithm is used to find a set of optimal loudspeaker positions from a larger possible loudspeaker positions. Loudspeakers are placed on the surface of opening at the wail. Using the measured acoustic transfer impedances and numerical simulations with the optimization technique, optimal positions we identified and compared. When a small number of loudspeakers are used, loudspeaker positions on the opening near the center seems to be the best place, but when a larger number of loudspeakers are used it was difficult to find simple patterns Un the optimal positions.

• 비파괴검사학회지
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• 제36권2호
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• pp.149-154
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• 2016

The use of nonlinear ultrasonics wave has been accepted as a promising tool for monitoring material states related to microstructural changes, as it has improved sensitivity compared to conventional non-destructive testing approaches. In this paper, third harmonic generation of shear horizontal guided waves propagating in an isotropic plate is investigated using the perturbation method and modal analysis approach. An experimental procedure is proposed to detect the third harmonics of shear horizontal guided waves by electromagnetic transducers. The strongly nonlinear response of shear horizontal guided waves is measured. The accumulative growth of relative acoustic nonlinear response with an increase of propagation distance is detected in this investigation. The experimental results agree with the theoretical prediction, and thus providing another indication of the feasibility of using higher harmonic generation of electromagnetic shear horizontal guided waves for material characterization.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.715-722
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• 2012

A structural health monitoring (SHM) technique for locating impact position in a composite plate is presented in this paper. The technique employs a single sensor and spatial focusing properties of time reversal (TR) and inverse filtering (IF). We first examine the focusing effect of back-propagated signal at the impact position and its surroundings through simulation. Impact experiments are then carried out and the localization images are found using the TR and IF signal processing, respectively. Both techniques provide accurate impact location results. Compared to existing techniques for locating impact or acoustic emission source, the proposed methods have the benefits of using a single sensor and not requiring knowledge of material properties and geometry of structures. Furthermore, it does not depend on a particular mode of dispersive Lamb waves that is frequently used in the SHM of plate-like structures.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.802-805
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• 1988

The objective of the present study was to manufacture the piezoelectric composites of Lead Zirconate Titanate (PZT) - polymer for applications such as ultrasonic medical diagnosis and hydrophone. The PZT rod-polymer composites have been prepared with 4.5 to 57 volume percent PZT using 1.5 mm rod, so the connectivity pattern of the two phase is 1-3 type. The electromechanical coupling factors of radial mode ($k_{p}$) and thickness mode ($k_{t}$) were nearly independent of the volume percent PZT, which were 0.3 and 0.65, respectively. The acoustic impedance of the piezoelectric composites was measured by the resonance technique in the frequency range 50 KHz-1.5 MHz, which was in the range of 3.8 - 60 Mrayl.

• 마이크로전자및패키징학회지
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• 제2권1호
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• pp.69-75
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• 1995

압전세라믹스를 제조하여 발음체 소자의 두께 직경등의 칫수 변화에 따른 압전발을 체 소자의 전기적 특성 및 압전세라믹스와 금속진동판의 상관관계를 조사하고 공명용 수지 case등을 고려하여 공진 주파수에서 효율좋은 음을 발생시킬수 있는 압전발음체를 설계하였 다. 본 실험에서 사용딘 압전세라믹스 (Pb0.95Sr0.05)(Zr0.53Ti0.47)O3+0.8wt%Nb2O5의 특성은 전 기기계 결합계수(KP)가 69%이며 기계적 품질계수(Qm)은 87 비유전율은 2100 tan$\delta$는 0.016이었다. 금속진동판의 공진주파수는 사용되는 재료의 stiffness와 관계가 있고 주파수 -impedance 특성은 재질의 음속, 밀도, Young율 등에 크게 의존하였다. 주파수 대역 2.0~ 2.2khz에서 공진시키기 위한 공명체의 설계에서 압전세라믹스의 외경과 두께가 각각 14mm, 0.1mm 이고 금속진동판의 그것이 각각 20mm, 0.1mmdlfEo 공명기는 방음공의 직경이 3.0mm, cavity의 직경이 18.5mm, cavity의 높이가 4.5mm의 구조로 설계되었을때가 최적조 건이었다.

• 한국음향학회지
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• 제15권1호
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• pp.40-45
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• 1996

이 논문에서는 최적의 빔패턴을 얻기 위한 비선형 최적 설계 기법을 제시하였다. 제시된 방법을 사용하여 진동체 사이의 자기 및 상호 방사 임피던스를 고려하여 최대 허용 부엽준위가 주어진 경우 빔폭이 최소화된 빔 패턴을 설계할 수 있다. 그리고 37개의 진동체가 X, Y 및 $45^{circ}$축에 대칭으로 배열된 평면 배열에 대해 제안된 기법을 적용한 결과 빔폭은 변화없이 상당히 낮은 부엽 준위를 얻었다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.194-196
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• 2005

Ultrasonic guided waves are gaining increasing attention for the inspection of platelike and rodlike structures. At the same time, inspection methods that do not require contact with the test piece are being developed for advanced applications. This paper capitalizes on recent advances in the areas of guided wave ultrasonics and noncontact ultrasonics to demonstrate a superior method for the nondestructive detection of thinning defects simulating hidden corrosion in thin aluminum plates. The proposed approach uses EMAT(electro-magnetic acoustic transducer) for the noncontact generation and detection of guided plate waves. Interesting features in the dispersive behavior of selected guided modes are used for the detection of plate thinning. It is shown that mode cutoff measurements provide a qualitative detection of thinning defects. Measurement of the mode group velocity can be also used to quantify of thinning depth.

• 전자공학회논문지A
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• 제32A권7호
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• pp.94-103
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• 1995

Thin film acoustooptic beam deflector in proton-exchanged Y-cut LiNbO$_{3}$ was fabricated and measured. The planar waveguide was fabricated by using the proton-exchanged and annealing method in Y0cut LiNbO$_{3}$. Interdigital transducer for SAW(surface acoustic wave) was made by the laser lithography. Using above method, the thin film acoustooptic beam deflector was constructed. Its SAW wavelength was 20.mu.m at 174MHz center frequency. The interaction length between guided optical wave and SAW was 2.16mm. The measured 3dB bandwidth was 17MHz using He-Ne laser. And 70% diffraction efficiency was obtained at 970mW RF driving power.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 전력전자학술대회
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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.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권5호
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• pp.263-266
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• 2006

An optical microphone was developed using a dual-core multi-mode fiber block and a membrane type micromirror. The fiber block serves as a compact optical head, and the micromirror as a reflective diaphragm. The micromirror is designed to be suspended through a silicon bar connected t a frame, allowing for displacement induced by acoustic waves. The optical head is implemented by integrating two multi-mode fibers in a single block, and used to transfer light signals between it and the diaphragm. For the assembled microphone, its static characteristics were observed to reveal the operating point defined as the optimum distance between the optical head and the diaphragm. And its dynamic response was tested to exhibit a frequency bandwidth of 3 kHz with the variation of $\sim5dB$.