• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.46-53
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• 2000

Magnetostrictive sensors which can be used effectively to detect flaws in pipe were fabricated. The optimal conditions to obtain the maximum generation efficiency of the ultrasonic wave were established. In case of the used steel pipe the optimal magnetic field was $250{\sim}350Oe$ and the coil width of 15mm showed the best efficiency for generating a wave with the frequency of 180 kHz. In the best condition, the wave can propagate further than 50m without serious attenuation. The amplitude of the ultrasonic wave reflected from artificial flaw had a good linear relationship to the cross-sectional area of the flaw.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2008.04a
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• pp.205-208
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• 2008

This paper propose a advanced technique for exciting and receiving the guided torsional wave to detect flaws in pipe systems. There are some difficulties in selecting and exciting of modes by using the nickel strip attached on pipe systems, such as qualification of residual magnetic field and multi-exciting of the unwanted modes etc. In order to there difficulties we propose the new sensor, so called Crossed-coils sensor. We will prove that it is possible to select the modes to be excited and to find a optimal excitation condition for torsional mode by using the proposed sensor.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.6
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• pp.856-862
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• 2008

This paper propose a advanced technique for exciting and receiving the guided torsional wave to detect flaws in pipe systems. There are some difficulties in selecting and exciting of modes by using the nickel strip attached on pipe systems, such as qualification of residual magnetic field and multi-exciting of the unwanted modes etc. In order to there difficulties we propose the new sensor, so called Crossed-coils sensor. We will prove that it is possible to select the modes to be excited and to find a optimal excitation condition for torsional mode by using the proposed sensor.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.1
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• pp.81-89
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• 1999

The fabrication process for miniaturizing the Electronic Article Surveillance (EAS) sensor was studied using micromachining technique. Two types of sensor structure, free standing membrane type and diving beard type, were proposed and researched for establishing the fabrication process. The membrane type structure was easy to change the sensor shape but had the limitation for miniaturizing, because the size of the sensor depends on the silicon substrate thickness. The diving board type structure has the advantage of miniaturization and of free motion. Since the elastic modulus is not trio high, SiN film is expected to be adequate for the supporting membrane of magnetic sensor. The selectivity of $H_2O_2$for sputtered W with respect to Fe-B-Si, which was studded for magnetic sensor materials, was high enough to be removed after using as a protection layer. Therefore, the diving board type process using the silicon nitride film for the supporter of the sensor material and the sputtered W for protection layer is expected to be useful fur miniaturizing the Electronic Article Surveillance (EAS) sensor.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.3
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• pp.395-400
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• 2013

In this paper, we introduce the implementation of high accurate level sensor system using the pulse wave type magnetostriction sensor. When a current pulse flows along the waveguide, the magnetic field also propagates towards the end of waveguide. When this magnetic field just passes the position of the magnet for level detection, the resultant magnetic field by these two magnetic fields makes a torsional reflected signal. This is used to calculate the time difference between a interrogation pulse wave and this torsional reflected signal. The key elements and characteristics were investigated to implement level sensor system based on this principle. We introduce a method to calculate the speed of ultrasonic reflected signal and how to make a model of sensing coil. In particular, we experiment with the characteristics of the torsional reflected signal according to the changes of the interrogation voltage and displacement. To make high accurate level sensor system, two methods were compared. One is to use the comparator and time counter, the other is STFT(Short Time FFT) which is capable of the time-frequency analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.636-642
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• 2014

The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and to estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. The reflection coefficients are calculated using the modal energies of the separated mode. Results from experimental results on a carbon steel pipe are presented, which show that the accurate and quantitative defect characterization could become enabled using the proposed technique.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.4
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• pp.324-331
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• 2014

The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet transform based on the maximum likelihood estimation, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. Simulation results on a carbon steel pipe are presented, which show the accurate mode separation and more discernible time-frequency representation could become enabled using the proposed technique.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.46-51
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• 2010

A torsional guided wave was applied to detect a defect in petrochemical pipes. Phase and group velocity dispersion curves for the longitudinal and torsional modes of the inspected pipe were presented for the theoretical analysis. It was found through mode shape analysis that there was mode conversion when torsional wave is incident at an asymmetric defect. An artificial notch was fabricated in the pipe and the detectability was examined from the distance 2m of the end of the pipe by using magnetostrictive sensors. The relativities between the amplitude of the reflected signal and the size of the defect was examined. It was shown that the T(0,1) mode could be used for the long range inspection for the petrochemical pipes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.841-848
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• 2010

Previous experimental results show that the magnetostrictive transducer has the peculiar characteristic with relation to their reversible magnetization and its practical usage will be hindered by this phenomena. In this paper, the idea of anhysteretization is adopted in order to solve this problem. The experimental results reveal that the anhysteretization can get rid of the extraordinary phenomena which are occurred by the change of biasing magnetic field. The effects of two important parameters, which are the amplitude and the decaying time of this process, on the anhysteretization are investigated experimentally. Finally the best operating condition is proposed in order to maximize the sensitivity under the anhysteretization.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.198-199
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• 2002

연자성 재료는 투자율이 높고, 큰 포화자속 밀도를 갖는 재료로서 외부자계에 용이하게 자화되며, 그 용도를 살펴보면 전기에너지 변환, 자기기록. 변압기, 변성기, 각종 코아, 모터, 자기센서, 전ㆍ자계차폐재등 많은 전자기기에 이용되고 있다. 따라서 연자성재료는 기본적으로 결정자기이방성과 자왜가 작아야 한다. 한편 전기, 전자기의 경량화 및 고효율화를 위하여서는 포화자속밀도의 극대화, 고주파영역에서의 우수한 연자기 특성 및 저에너지 손실을 갖는 재료개발이 요구된다. (중략)