• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.41-45
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• 2006

The fabrication process of fiber placement system of carbon fiber reinforced plastic (CFRP) requires real time process control and reliable inspection to ensure quality by preventing defects such as delamination and void. Therefore, novel non-contact inspection technique is required during the non-destructive evaluation in a fiber placement system. For the inspection of delamination in CFRP, various methods to receive laser-generated ultrasound were applied by using piezoelectric transducer, air-coupled transducer, wavelet transform and scanning laser ultrasonic technique. Laser-generated ultrasound was received with a conventional piezoelectric sensor in contacting manner. Then signal characteristics due to defects were analyzed to find a factor for detecting defects. Air-coupled transducer was used for reception of laser-generated guided wave using linear slit array in order to generate high frequency guided wave. And line scan technique was used to confirm the capability of on-line application. The high frequency component of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. Nevertheless, it was failed to receive high frequency guided wave in using air-coupled transducer. The first peak of the frequency spectrum under 100kHz in the delamination region is higher than in the sound region. By using this feature, the line scanned frequency data were acquired in fully non-contact generation and reception of ultrasound. This method was proved as useful technique for detecting delamination in CFRP.

• Smart Structures and Systems
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• 제14권3호
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• pp.267-284
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• 2014

This paper aims to present the analytical solutions of 2-2 cement based piezoelectric transducers in series electrically based on the theory of piezo-elastic dynamics. The solutions of two different kinds of 2-2 cement based piezoelectric transducers under external harmonic load are obtained by using the displacement method. The effects of electrical connection of piezoelectric layers, loading frequency, thickness and distance of piezoelectric layers on the characteristics of the transducers are discussed. Comparisons with other related experimental investigations are also given, and good agreement is found. The proposed 2-2 cement based piezoelectric transducers have a great potential application in monitoring structural health in civil engineering and capturing mechanical energy or monitoring train-running safety in railway system and traffic safety in road system.

• Composites Research
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• 제20권3호
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• pp.31-36
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• 2007

본 연구는 압전 변환기를 이용하여 탄소/에폭시 복합재료 보의 초기 균열 길이에 대한 정량적인 예측방법을 제시하였다. 구조물의 손상에 대한 비파괴평가기술에 대한 관심은 증가하고 있다. 본 연구에서는 시간-주파수 영역에서 웨이블렛 변환에 기초한 신호처리기술로 손상 유무와 손상평가를 위한 방법을 제시하였다. 한 쌍의 피에조 재료를 이용하여 탄소/에폭시 복합재료 보의 동적응답을 제안한 신호처리 기술로 협대역 가진하에서 연구하였다.

• 한국해양공학회지
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• 제22권2호
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• pp.65-71
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• 2008

Recently, many researches in relation to data transmission with faster speed and greater volume, many researches have been carried out on sonar systems for underwater communication. According to these researches, an acoustic transducer for underwater communication requires wide bandwidth properties. In domestic researches for underwater communication sonar, an operating frequency in the range of $20{\sim}40\;kHz$ is used. In this paper, we propose anon-resonance type acoustic transducer for underwater communication. The TVR (transmitting voltage response) characteristics increased linearly as the frequency increased, and the RVS (receiving voltage sensitivity) characteristics were constant as the frequency increased. Traditional techniques for wide bandwidth transducershave a limit and a transmission loss difference at lower and higher frequency operating ranges. In this paper, the new transducer proposed decreased the transmission loss under some conditions. It was optimized with the FE analysis tool (ATILA) and evaluated using the TVR and the RVS characteristics in the range of $10{\sim}90\;kHz$. The value of TVR was 138 dB at 20 kHz and 148 dB at 40 kHz, and the differences was 12 dB. The value of RVS was $195{\pm}2\;dB$ and nearly constant. From theseresults, it is certain that the developed transducers can be used for an underwater communication network in the 1.3 km range with both a 20 kHz bandwidth and 30 kHz center frequency.

• Smart Structures and Systems
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• 제22권4호
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• pp.369-382
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• 2018

Novel design of interdigitated electrodes capable of increasing the performance of piezoelectric transducers are proposed. The new electrodes' geometry improve the electromechanical coupling by offering an enhanced adaptation of the electric field to the interdigitated electrode configuration. The proposed analysis is based on finite element modeling and takes into account local polarization effect. It is shown that the proposed electrodes considerably increase the strain generation compared to flat electrode arrangement used for Macro Fiber Composite (MFC) and Active Fiber Composite (AFC) actuators. Also, electric field singularities are reduced allowing better reliability of the transducer against electric failure.

• Smart Structures and Systems
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• 제30권4호
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• pp.371-383
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• 2022

A novel impact localization method is presented based on impact induced elastic waves in sensorized composite structure subjected to temperature fluctuations. In real practices, environmental and operational conditions influence the acquired signals and consequently make the feature (particularly Time of Arrival (TOA)) extraction process, complicated and troublesome. To overcome this complication, a robust TOA estimation method is proposed based on the times in which the absolute amplitude of the signal reaches to a specific amplitude value. The presented method requires prior knowledge about the normalized wave velocity in different directions of propagation. To this aim, a finite element model of the plate was built in ABAQUS/CAE. The impact location is then highlighted by calculating an error value at different points of the structure. The efficiency of the developed impact localization technique is experimentally evaluated by dropping steel balls with different energies on a carbon fiber composite plate with different temperatures. It is demonstrated that the developed technique is able to localize impacts with different energies even in the presence of noise and temperature fluctuations.

• Composites Research
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• 제28권4호
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• pp.148-154
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• 2015

구조건전성 모니터링은 구조물에 발생된 손상을 조기에 감지 및 적절한 유지보수를 통해 재정적 혹은 인명 피해를 방지하기 위해 실시된다. 대부분의 능동센싱 기반 구조건전성 모니터링에서는 많은 수의 압전체(piezoelectric transducer) 센서와 구동기(actuator)를 필요로 한다. 구조건전성 모니터링 시 사용된 압전센서에 결합이 존재하는 경우, 구조물의 상태진단에 문제가 발생할 수 있다. 본 연구에서는 신뢰성 있는 구조건전성 모니터링 결과를 위해 임피던스 기반 센서 자가 진단법을 사용하여 다수 센서의 결함을 탐지하였다. 또한 사용된 접착제와 센서의 정보가 충분치 못한 경우, 사용된 센서로부터 측정된 데이터만을 토대로 센서결함 진단을 위한 알고리즘을 소개하였다. 알고리즘이 적용 가능한 온도 범위를 실험적으로 분석함으로써 개발된 기법이 실제 환경에서 응용이 가능함을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1537-1539
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• 1998

In this study, 3-D underwater object restoration using ultrasonic transducer fabricated with PZT-Polymer 1-3 type composite are presented. Using the acquired underwater object data 16${\times}$16 pixels. Modified SCL neural networks using the 16${\times}$16 low resolution image was used for underwater object restoration of 32${\times}$32 high resolution Image.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.303-306
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• 1999

In this study, the piezoelectric ceramics PZT powder was synthesized by Wet-Dry combination method. The flexible 1-3-0 type composites were fabricated with piezoceramic PZT and Eccogel polymer matrix embedded 3rd phase. This paper represents the acoustic properties with various 3rd phase wt.%. The acoustic impedance of 1-3-0 type composites was lower than that of single phase PZT ceramics. The pulse-echo response of transducer fabricated with 1-3-0 type composites was better than solid PZT transducer.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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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.