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Laser/EMAT-Array System for Non-Destructive Evaluation.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Laser/EMAT-Array System for Non-Destructive Evaluation./
作者:	Dutton, Benjamin.
面頁冊數:	1 online resource (246 pages)
附註:	Source: Dissertations Abstracts International, Volume: 80-07, Section: C.
Contained By:	Dissertations Abstracts International80-07C.
標題:	Chemical engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13805149click for full text (PQDT)
ISBN:	9780438735040

Laser/EMAT-Array System for Non-Destructive Evaluation.
Dutton, Benjamin.

Laser/EMAT-Array System for Non-Destructive Evaluation. - 1 online resource (246 pages)

Source: Dissertations Abstracts International, Volume: 80-07, Section: C.

Thesis (Ph.D.)--The University of Manchester (United Kingdom), 2007.

Includes bibliographical references

A novel laser/EMAT-array system has been developed using a unique magnetic field enhancement design to boost the pickup signal from the EMAT. It offers a non-contact non-destructive evaluation (NDE) system using ultrasound for both generation and detection. The potential of a laser/EMAT system is first demonstrated in a material characterization measurement performed on nuclear graphite samples with various levels of oxidation. Longitudinal velocity measurements were used to estimate Young's modulus for graphite samples with parallel and perpendicular microstructures, where velocity variations were detected for these two types of microstructures. More interestingly, velocity variations were also detected when samples were rotated about their cylindrical axis. This may be the first time that an acoustic birefringence effect has been observed in porous graphite. After creating 3D theoretical models of several magnetic configurations, a configuration with an enhanced magnetic flux density was applied to EMATs sensitive to in-plane (IP) or out-of-plane (OP) ultrasound vibration. This magnetic flux density enhancement resulted in improved EMAT performance. Enhanced IP EMAT characteristics were compared to a previous IP EMAT, where SNRs were 16.5 and 8.3 and resonance frequencies were 17.5 MHz and 8.0 MHz respectively. Similar enhancements were applied to develop an OP EMAT, where in-vivo tissue measurements were carried out. Although ultrasound waveforms were positively detected when the sensor was in contact with sample, it is shown that measurements were not detected by the known EMAT mechanism since predicted voltage levels for tissue were -4 orders of magnitude below noise levels. Signals were thought to have been detected by ultrasound induced mechanical vibrations of the EMAT coil. Instrumentation for an OP EMAT-array was developed using 8 EMAT elements, based on enhanced EMAT design. Sensitivity and calibration measurements were taken to assess array performance, and were compared to a previous single EMAT. Displacement sensitivities of an EMAT-array and a single EMAT were 1.25 mV nm-1 and 0.99 mV nm-1 respectively. Additionally, the minimum detectable displacements for an EMAT-array and a single EMAT were 52 pm and 71 pm respectively. From crosstalk and noise level measurements, it was noted that detected signals were affected more by noise than by crosstalk by -12 dB. The array system proved to be a successful tool in a number of applications. Due to high precision (better than 99%) velocity measurements, anisotropy in metals was examined. In a separate application, detected Lamb waveform variations were used to indicate areas where delamination occurred in a plasma coated nickel alloy. Ultimately, the laser/EMAT-array system generated real-time B-scans in a transmission mode, and real-time B-scans and C-scans in a reflection mode.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9780438735040Subjects--Topical Terms:

560457
Chemical engineering.
Subjects--Index Terms:

Electromagnetic acoustic transducerIndex Terms--Genre/Form:

542853
Electronic books.

Laser/EMAT-Array System for Non-Destructive Evaluation.
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520 $a A novel laser/EMAT-array system has been developed using a unique magnetic field enhancement design to boost the pickup signal from the EMAT. It offers a non-contact non-destructive evaluation (NDE) system using ultrasound for both generation and detection. The potential of a laser/EMAT system is first demonstrated in a material characterization measurement performed on nuclear graphite samples with various levels of oxidation. Longitudinal velocity measurements were used to estimate Young's modulus for graphite samples with parallel and perpendicular microstructures, where velocity variations were detected for these two types of microstructures. More interestingly, velocity variations were also detected when samples were rotated about their cylindrical axis. This may be the first time that an acoustic birefringence effect has been observed in porous graphite. After creating 3D theoretical models of several magnetic configurations, a configuration with an enhanced magnetic flux density was applied to EMATs sensitive to in-plane (IP) or out-of-plane (OP) ultrasound vibration. This magnetic flux density enhancement resulted in improved EMAT performance. Enhanced IP EMAT characteristics were compared to a previous IP EMAT, where SNRs were 16.5 and 8.3 and resonance frequencies were 17.5 MHz and 8.0 MHz respectively. Similar enhancements were applied to develop an OP EMAT, where in-vivo tissue measurements were carried out. Although ultrasound waveforms were positively detected when the sensor was in contact with sample, it is shown that measurements were not detected by the known EMAT mechanism since predicted voltage levels for tissue were -4 orders of magnitude below noise levels. Signals were thought to have been detected by ultrasound induced mechanical vibrations of the EMAT coil. Instrumentation for an OP EMAT-array was developed using 8 EMAT elements, based on enhanced EMAT design. Sensitivity and calibration measurements were taken to assess array performance, and were compared to a previous single EMAT. Displacement sensitivities of an EMAT-array and a single EMAT were 1.25 mV nm-1 and 0.99 mV nm-1 respectively. Additionally, the minimum detectable displacements for an EMAT-array and a single EMAT were 52 pm and 71 pm respectively. From crosstalk and noise level measurements, it was noted that detected signals were affected more by noise than by crosstalk by -12 dB. The array system proved to be a successful tool in a number of applications. Due to high precision (better than 99%) velocity measurements, anisotropy in metals was examined. In a separate application, detected Lamb waveform variations were used to indicate areas where delamination occurred in a plasma coated nickel alloy. Ultimately, the laser/EMAT-array system generated real-time B-scans in a transmission mode, and real-time B-scans and C-scans in a reflection mode.
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