• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.549-555
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• 2003

The objective of かis study is to investigate the feasibility of piezoelectric transducers as a damage detection system for civil infrastructures. There have been considerable amount of efforts by the modal analysis community to localize damage and evaluate its severity without looking at a reliable way to excite the structure. The detection of damages by modal analysis and similar vibration techniques depends upon the knowledge and estimation of various modal parameters. In addition to the associated difficulties, such low-frequency dynamic response based techniques fail to detect incipient damages. Smart piezoelectric ceramic (PZT) transducers which act as both actuators and sensors in a self-analyzing manner are emerging to be effective in non-parametric health monitoring of structural systems. In this paper, we present the results of an experimental study for the detection of damages using smart PZT transducers on the steel plate. The method of extracting the impedance characteristics of the PZT transducer, which is electro-mechanically coupled to the host structure, is adopted for damage detection. Two damages are simulated and assessed by the bonded PZT transducers for characterization. The experimental results verified the efficacy of the proposed approach and provided a demonstration of good robustness at the realistic steel structures, emphasizing the great potential for developing an automated in situ structural health monitoring system for application to large civil infrastructures without the need to blow the modal parameters.

• Smart Structures and Systems
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• v.26 no.6
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• pp.735-751
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• 2020

Identification of structure parameters is crucial in Structural Health Monitoring (SHM) context for activities such as model validation, damage assessment and signal processing of structure response. In this paper, guided waves generated by piezoelectric transducers are used for in-situ and non-destructive structural parameter estimation based on Bayesian approach. As Bayesian approach needs iterative process, which is computationally expensive, this paper proposes a method in which an analytical model is selected and developed in order to decrease computational time and complexity of modeling. An experimental set-up is implemented to estimate three target elastic and geometrical parameters: Young's modulus, Poisson ratio and thickness of aluminum and steel plates. Experimental and simulated data are combined in a Bayesian framework for parameter identification. A significant accuracy is achieved regarding estimation of target parameters with maximum error of 8, 11 and 17 percent respectively. Moreover, the limitation of analytical model concerning boundary reflections is addressed and managed experimentally. Pulse excitation is selected as it can excite the structure in a wide frequency range contrary to conventional tone burst excitation. The results show that the proposed non-destructive method can be used in service for estimation of material and geometrical properties of structure in industrial applications.

• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.54-58
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• 1990

홀 결모양(single mode) 광섬유로 조절가능한 곬진 짝짓게(tunable directional couplr)를 제작해 이중 공진 고리 간섭계(double resonant ing interferometer)를 구성했다. 이중 공진 고기 간섭계에 PZT(piezoelectric transducer)와 스피커를 각각 부착해서 위상 변조(phase modulation)를 동시에 시켜 나오는 출력 신호가 전산 시늉(computer simulation)을 통해 얻은 결과와 일치함을 보았으며, 이 출력 신호를 FFT(Fast Fourier Transformation)를 써서 분석했다. 이 결과로부터 동시에 두 가지 외부 변화를 감지할 수 있는지를 조사했다.

• 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.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.160-167
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• 1996

A new pathlength deviation detection technique which is composed of michelson interferometer is described and verified experimentally. The technique uses a sub-threshold biased visible laser diode of 20$\mu$m coherence length as a low-coherent light source. And for zeroth-order fringe(which is the largest among fringes) identification we used a piezoelectric transducer with a large modulation smplitude, which enables without the need of constant velocity scanning, to distinguish reflection surfaces separated by more than 10$\mu$m with a resolution of less than half-wavelength.

• 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.

• Journal of KSNVE
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• v.6 no.6
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• pp.749-754
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• 1996

In this paper, a design method of matching layers is presented for the sandwich type broad band underwater acoustic vibrators. The characteristic impedances of matching layers are determined to be matched to the characteristic impedance of head mass material. For the dynamic characteristic analysis of the sandwich type transducers, one dimensional FEM technique is also introduced. A test vibrator with the quarter wave matching layers has been designed to verify the proposed method. And the wide band characteristics of the input impedance and transmitting voltage response (TVR) are investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1012-1016
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• 1996

This paper presents an automatic calibration technique for piezoelectic low pressure transducer, which is useful to measure a pressure within 500 psi. This system with automatic calibration function and error correction algorithm generates standard dynamic pressure for the calibration of sensor. With the compensation for the offset voltage and the pressure error, the accuracy and the usefulness of the proposed scheme is validated.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.11
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• pp.88-98
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• 1993

In this paper, the effective permittivity in the piezoelectric material is numerically obtained and greens function is derived from that. It is shown that the admittance and the transfer function of an interdigital transducer is represented by electrostatic charge distribution using Quasi-static approximation. To prove the validity of the quasi-static approximation, numerical results for the uniform IDT of a filter mounted on 128 $^{\circ}$ rotated Y-cut X-propagating Lithium Niobate are compared with the measured ones.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.1
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• pp.37-43
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• 1998

This article describes the application of a coupled finite element-boundary element method to obtain the steady-state response of a sonar transducer. The particular structure considered is a flooded piezoelectric spherical shell. The sonar shell is simulated to be driven by electrical charges applied onto inner and outer surfaces of the shell. It is shown that at relatively low input frequency a beam pattern which is almost close to omnidirection can be obtained. The coupled FE-BE method is described in detail.