• 한국소음진동공학회논문집
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• 제24권2호
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• pp.123-130
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• 2014

An ultrasonic magnetostrictive transducer-based phased-array system for imaging defects in plate structures is newly proposed. In that most ultrasonic phased array systems rely on piezoelectric transducers or electromagnetic acoustic transducers, this system has its own unique feature of employing magnetostrictive transducers. Interest in using a phased array system using magnetostrictive transducers has been recently reported for pipe inspection but no such system has been developed for plate inspection. In this investigation, we aim to propose a phased array system using OL-MPTs (Omnidirectional Lamb wave Magnetostrictive Patch Transducers) for plate inspection. The developed system consists of a multi-channel function generator, power amplifiers, preamplifiers and a data acquisition unit. In the process of its development, each of the units must be checked and in doing so, we suggest types of ultrasonic wave experiments that should be carried out. Finally, the phased system using a transducer array composed of eight OL-MPTs is newly configured and is applied for actual crack detection experiments.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.856-859
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• 2005

The OPMT(Orientation-adjustable Patch-type Magnetostrictive Transducer) was proposed as a tool for generating and measuring the ultrasonic Lamb wave in plate type structures. This sensor has a lot of new features compared to the traditional piezo-type ultrasonic transducers. As an example, it does not need any kind of wiring for lunching or measuring ultrasonic waves. But it has also definite limitation for practical usage as a nondestructive testing tool in that it cannot help rotating the direction of ultrasonic wave manually. The idea for 'scanning OPMT' is proposed in this respect. Two kinds of basic ideas for rotating the wave direction not manually but electrically are proposed. The fabrication of the transducer and the testing for Identifying the primary characteristics are done for one of the proposed transducers. The results says that there are the possibilities as a new tool for NDE in that the proposed transducer follows well the characteristics of the traditional OPMT. But there are also the 1imitations to overcome.

• 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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.423-427
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• 2004

In this work, we propose a new ultrasonic damage inspection method in plate structures. The proposed method employs an OPMT (Orientation-adjustable Patch-type Magnetostrictive Transducer) in order to make the ultrasonic waves focused on the specific target point. For experiments, virtual grid points were set up at every 50 mm in an aluminum plate and two OPMTs were used for inspection. If there exists a crack in a plate, the reflected Lamb wave from the crack is measured in addition to the direct waves from the transmitting transducer to the receiving transducer.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.776-783
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• 2020

As the refueling of a sodium-cooled fast reactor is conducted by rotating part of the reactor head without opening it, the monitoring of existing obstacles that can disturb the rotation of the reactor head is one of the most important issues. This paper deals with the ultrasonic ranging technique that directly monitors the existence of possible obstacles located in a lateral gap between the upper internal structure and the reactor core in a prototype generation IV sodium-cooled fast reactor (PGSFR). A 10 m long plate-type ultrasonic waveguide sensor, whose feasibility has been successfully demonstrated through preliminary tests, was employed for the ultrasonic ranging technique. The design of the sensor's wave radiating section was modified to improve the radiation performance, and the radiated field was investigated through beam profile measurements. A test facility simulating the lower part of the upper internal structure and the upper part of the reactor core with the same shapes and sizes as those in the PGSFR was newly constructed. Several under-water performance tests were then carried out at room temperature to investigate the applicability of the developed ranging technique using the plate-type ultrasonic waveguide sensor with the actual geometry of the PGSFR's internal structures.

• Smart Structures and Systems
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• 제4권3호
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• pp.291-304
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• 2008

Piezoelectric materials have been widely used in ultrasonic nondestructive testing (NDT). PZT ceramics can be used to receive and generate surface acoustic waves. It is a common application to attach PZT transducers to the surface of structures for detecting cracks in nondestructive testing. However, not until recently have piezoelectric polymers attracted more and more attention to be the material for interdigitated (IDT) surface and guided-wave transducers. In this paper, an interdigitated gold-on-polyvinylidene fluoride (PVDF) transducer for actuating and sensing Lamb waves has been introduced. A specific etching technology is employed for making the surface electrodes into a certain finger pattern, the spacings of which yield different single mode responses of Lamb waves. Experiments have been performed on steel and carbon fiber composite plates. Results from PVDF IDT sensors have been compared with those from PZT transducers for verification.

• 비파괴검사학회지
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• 제26권1호
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• pp.18-24
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• 2006

액체금속로 원자로 노심과 내부구조물 들은 불투명한 소듐 내에 잠겨 있어 육안검사를 수행할 수 없다. 액체금속로 내부구조물의 육안검사를 수행하기 위해서는 초음파를 이용한 소듐내부 가시화가 적용되어야 한다. 본 연구에서는 소듐내부 가시화에 적용하기 위한 판형 초음파 웨이브가이드 센서를 개발하였다. 웨이브가이드 센서에서의 판파 전파특성을 분석하고 판파 적용모드로 제0차 반대칭 $A_0$ 모드를 선정하였다 웨이브가이드 센서에 액체 웨지를 적용하여 $A_0$ 모드의 저주파수 분산 영역에서 판파가 발진되도록 하였으며 입사펄스의 주파수 변조에 의하여 초음파 빔 방사각을 변환시킬 수 있는 새로운 방법을 제안하였다 본 방법은 웨이브가이드 센서를 기계적으로 구동하지 않고 빔 방사각을 조정할 수 있어 기존 웨이브가이드 센서의 구동 제한성을 극복할 수 있게 해 준다. 웨이브가이드 센서의 빔 방사각 변환 특성을 실험적으로 검증하였으며, 수중 C-스캔 시험을 수행하여 웨이브가이드 센서의 소듐내부 가시화 적용 가능성을 확인하였다.

• 비파괴검사학회지
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• 제33권3호
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• pp.264-269
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• 2013

Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.

• 비파괴검사학회지
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• 제28권4호
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• pp.364-371
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• 2008

소듐냉각고속로 원자로 내부구조물의 소듐내부가시화를 위한 새로운 웨이브가이드 초음파센서를 개발하였다. 소듐냉각고속로에 적용할 수 있는 웨이브가이드 초음파센서 어셈블리의 구조 설계 개념을 제시하고 그 적용 타당성을 평가하였다. 길이가 10 m인 웨이브가이드 초음파센서 어셈블리를 제작하고 성능평가 시험을 수행하였다. $A_0$ 모드 판파의 장거리 전파 성능을 확인하였으며, 수중 C-스캔 분해능 성능시험을 수행하여 웨이브가이드 초음파센서의 적용 가능성을 실험적으로 검증하였다.

• 한국음향학회지
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• 제22권1호
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• pp.61-68
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• 2003

유도초음파는 얇은 판재와 다층재료를 평가하는데 널리 사용되는데, 이를 정량적으로 이용하기 위해서는 위상 및 군속도의 분산 곡선은 필수적이다. 본 연구에서는 누수 램파의 후방복사 신호를 측정하기 위한 측정장치를 개발하였다. 시험편을 회전시켜서 입사각을 변화시켰으며, 2차원 평면에서 움직이면서 입사 위치를 바꾸었다. 광대역 초음파 탐촉자를 사용하여 탄성판에서 발생하는 누수 램파 후방복사 신호를 측정하였다. 입사각으로부터 위상속도가 결정되며, 이에 해당하는 램파의 특정모드가 판재 내에 강하게 발생되고, 이 램파는 시험편의 앞뒤로 진행하면서 물속으로 에너지를 방출한다. 동일한 탐촉자를 사용하여 누수 램파의 후방복사 신호를 검출하고, 이 신호의 주파수 성분은 분산곡선에 대한 정보를 지닌다. 입사각도와 수신된 파형의 주파수 분석을 통하여 램파의 위상속도 분산곡선을 구하였다. 또한 특정한 입사각에서 입사점을 변화시키면서 초음파 신호의 시간대역 이동으로부터 군속도를 측정하였다.