• 수산해양기술연구
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• 제19권2호
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• pp.93-98
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• 1983

When detecting underwater targets using echo sounder, the echo signals varies with the angular displacement of the transducer due to ship's motion. Then, the effect of the angular which effects the capability of the echo sounder must be investigated in relation to the detection of fish concentration, particularly, the abundance estimation of fish. In this pater, as the basic research to investigate the effect of the ship's motion when estimating the fish stocks by acoustic methods, the authors was theoritically considered the variations in the values of the two way directivity function of transducer in the direction of the targets which caused by the angular motion of transducer. Here, the effects of the movement of target and ship's running are neglected. At the same time, the data was applied to estimate the angular shift of the detectable area of echo sounder due to transducer displacement. From the results analyzed, we found that the angular shift of the detectable area due to ship's motion increases both as the roll angle increases and as the beamwidth becomes narrower, varies with the depth.

• E2M - 전기 전자와 첨단 소재
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• 제9권10호
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• pp.1053-1059
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• 1996

The pulse-echo response of the piezoceramics PZT-polymer 3-3 type composite transducers with various PVA additions were investigated. The PZT powder was prepared by the molten salt synthesis method. The porous PZT specimens will be used as a filler to make 3-3 type comosite were prepared from a mixture of PZT and polyvinylalcohol(PVA) sphere by utilizing BURPS(Bumout Plastic Sphere) technique. It was shown that the transmitting and receiving sensitivity of 3-3 type piezoelectric composite transducers could be improved than that of solid PZT transducers. The reason is that 3-3 type piezoelectric composite have low dielectric constant, density and acoustic impedance. The distance between transducer and reflector was in good agreement with the distance calculated from the longitudinal velocity of the specimens and receiving time observed pulse-echo responses on the ultrasonic transducer analyzer.

• Smart Structures and Systems
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• 제24권4호
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• pp.435-446
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• 2019

The existing piezoelectric spherical transducers with fixed prescribed dynamic characteristics limit their application in scenarios with multi-frequency or frequency variation requirement. To address this issue, this work proposes an improved design of piezoelectric spherical transducers using the resistance tuning method. Two piezoceramic shells are the functional elements with one for actuation and the other for tuning through the variation of load resistance. The theoretical model of the proposed design is given based on our previous work. The effects of the resistance, the middle surface radius and the thickness of the epoxy adhesive layer on the dynamic characteristics of the transducer are explored by numerical analysis. The numerical results show that the multi-frequency characteristics of the transducer can be obtained by tuning the resistance, and its electromechanical coupling coefficient can be optimized by a matching resistance. The proposed design and derived theoretical solution are validated by comparing with the literature given special examples as well as an experimental study. The present study demonstrates the feasibility of using the proposed design to realize the multi-frequency characteristics, which is helpful to improve the performance of piezoelectric spherical transducers used in underwater acoustic detection, hydrophones, and the spherical smart aggregate (SSA) used in civil structural health monitoring, enhancing their operation at the multiple working frequencies to meet different application requirements.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.401-402
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• 2010

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 추계학술발표대회논문집 제23권 2호
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• pp.429-432
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• 2004

Nonlinear acoustic responses of water-saturated sediments are very important to understand nonlinear phenomena of gassy ocean sediments. Especially, the second harmonic, the sum and the difference frequency acoustic waves in water-saturated sediments can provide practical criteria to estimate the nonlinear parameter of gassy sediments. In this paper, the difference frequency acoustic wave in water-saturated sandy sediment was observed in a water tank experiment with a pulse transmission technique. Its pressure level was 12 dB higher than the background noise level at a maximum undistorted driving pressure of source acoustic transducer. The experimental results were compared with a theoretical estimation of the parametric acoustic array. The nonlinear parameter of water-saturated sandy sediment was also estimated as 73 with their comparison. This value can be utilized as the background information to estimate gas void fraction in the water-saturated gassy sandy sediment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.1870-1872
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• 2005

In this study, an ultrasonic level limit sensor with a new structure utilizing the acoustic impedance matching is proposed to be able to check it out a change of water-level. 2 PZT resonators with the same property are bonded directly on the polyethylene plate. One resonator is for transmitter as an ultrasonic transducer, the other one is for receiver. In this case, a polyethylene plate will operate as an acoustic guider to transmit a transverse wave between 2 PZT resonators in air. While in the water, a polyethylene plate having a similar acoustic impedance with the water will be emitted an acoustic energy into the water as a longitudinal wave. According to this mechanism, there was a wide difference of acoustic signal output between underwater and in air. As a summary, this proposed level limit sensor could be used as a strong candidate with low cost and more stable one.

• 비파괴검사학회지
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• 제33권1호
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• pp.54-62
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• 2013

본 연구는 비접촉 무전원 표면탄성파(surface acoustic wave, SAW) 온도센서를 개발하기 위하여 수행되었다. 단일전극 구조의 IDT(inter-digital transducer)와 434 MHz의 공진주파수를 가지는 SAW 소자를 $128^{\circ}$ rot-X $LiNbO_3$ 압전기판위에 반도체 공정으로 제작하였다. SAW 온도센서의 음향 반사판에 따른 반사 신호의 특성을 분석하기 위하여 다양한 형태의 음향 반사판을 제작하여 표면탄성파 신호의 반사특성을 분석한 결과 빗살형 전극형태의 반사판이 가장 양호한 반사특성을 나타내었다. SAW 온도센서를 구동하기 위한 신호를 송신하고 온도에 따른 SAW 센서의 출력신호를 수신하기 위하여 다이폴 안테나와 마이크로프로세서에 기반한 무선 송수신 시스템을 제작하였다. $40{\sim}80^{\circ}C$의 온도 범위에서 개발된 SAW 온도센서와 무선 송수신 시스템을 평가한 결과 온도증가에 따라 SAW 온도센서의 공진 주파수가 선형적으로 감소하였으며 결정계수가 0.99 이상으로 정확한 무선 온도측정이 가능한 것으로 나타났다.

• 한국생산제조학회지
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• 제23권1호
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• pp.27-31
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• 2014

This paper describes a tomographic imaging technique for evaluating the thickness reduction of a plate-like structure using a noncontact sensor network based on an electromagnetic acoustic transducer that generates shear horizontal plate waves. Because this technique is based on the effect of mode cutoff and time of flight of guided waves caused by a change in thickness, the tomographic image provides information on the presence of defects in the structure. To verify the performance of the method, artificial defects with various thickness reduction ratios were machined in an aluminum plate, and the tomographic imaging results are reported. The results show that the generated tomographic image displays the thickness reductions and can identify their locations. Therefore, the proposed technique has good potential as a tool for health monitoring of the integrity of plate-like structures.

• 비파괴검사학회지
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• 제17권4호
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• pp.278-284
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• 1997

EMAT는 비접촉으로 초음파를 송수신 할 수 있는 탐촉자로서 시험체와 탐촉자간의 접촉을 위한 매개 물질이 필요치 않으므로, 움직이고 있는 물체에 초음파탐상법을 적용하고자 하는 분야와 초음파의 속도를 정밀하게 측정하고자 하는 분야에 주로 응용된다. 구체적으로는 길이가 긴 튜브류의 결함 탐상, 용접중인 재료의 용접상태 감시, 기차바퀴 및 레일의 결함 탐상, 고온상태인 재료의 결함 탐상 등이 비접촉 특성을 이용하여 적용될 수 있는 분야이며, 재료의 집합조직 및 소성이방성의 측정, 재료의 미세조직 및 기계적 강도의 예측, 그리고 잔류응력의 측정 등이 정밀한 초음파속도 및 감쇠의 측정으로부터 적용될 수 있는 분야이다. EMAT가 일반적인 접촉식초음파탐상법에 비하여 특별한 분야에의 응용에 큰 장점을 가지고 있지만, 낮은 에너지 전환효율, 넓은 불감영역, 그리고 사용주파수의 한계 등의 문제를 가지고 있기 때문에 기존의 접촉식 방법의 적용이 용이한 분야에의 적용은 필요하지 않다. 그러나 특별한 목적과 용도에의 적용 필요성이 생길 경우에는 적절한 연구를 통하여 알맞은 탐촉자를 제작하고 탐상 방법을 개발함으로서 본래의 목적에 알맞은 탐상이 수행될 수 있다.

• Nuclear Engineering and Technology
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• 제47권2호
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• pp.196-203
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• 2015

The aim of this work is to demonstrate a method for exciting and receiving torsional and longitudinal mode guided waves with an electromagnetic acoustic transducer (EMAT) ring array. First of all, a three-dimensional guided wave simulator is developed in order to numerically analyze the propagation of the guided wave. The finite difference time domain method is used for the simulator. Second, two guided wave testing systems using an EMAT ring array are provided: one is for torsional mode (T-mode) guided wave and the other is for longitudinal mode (L-mode). The EMATs used in the both systems are the same in design. A method to generate and receive the T- and L-mode guided waves with the same EMAT is proposed. Finally, experimental and numerical results are compared and discussed. The results of experiments and simulation agree well, showing the potential of the EMAT ring array as a mode controllable guided wave transmitter and receiver.