Study on the lift-off effect of EMAT

Huang, Songling; Zhao, Wei; Zhang, Yongsheng; Wang, Shen

doi:10.1016/j.sna.2009.05.014

Cited by 69 publications

(41 citation statements)

References 10 publications

(1 reference statement)

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“…As expected, there is a decrease in signal amplitude and SNR with increasing lift-off, although not as distinctly as predicted. It is reported widely in the literature that signal amplitude decreases exponentially with increasing lift-off for EMATs [14], with lift-off values of around 1 mm exhibiting a significant effect on SNR. Although first back-wall echo SNR exhibits a decrease from 35.…”

Section: Sample Bmentioning

confidence: 94%

Shear wave EMAT thickness measurements of low carbon steel at 450 °C without cooling

Lunn¹,

Potter²,

Dixon³

2017

AIP Conference Proceedings

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Abstract. Performing high temperature online inspection without plant shutdown is highly desirable, yet, development of portable or permanently installed high temperature ultrasonic sensors, without the need for sample surface preparation, remains a key challenge. Low carbon steel pipelines operating at elevated temperatures often develop a magnetostrictive oxide coating (magnetite), which improves electromagnetic acoustic transducer (EMAT) efficiency below the Curie temperature of magnetite (575 ˚C), via a magnetostrictive mechanism. Coupling the inherent non-contacting nature of EMATs with the enhanced efficiency from a magnetite coating, we are able to continuously operate an uncoded EMAT at elevated temperatures without permanent installation or surface preparation. In this work, a high temperature shear wave EMAT utilizing a high field, high Curie point, permanent magnet has been developed to generate ultrasonic bulk thickness measurements on magnetite coated steel at temperatures of up to 450 ˚C, without cooling. Relatively high signal-to-noise ratios, in the region of 30 dB for single shot data, have been measured at 450 ˚C using this technique. The EMAT design and results from high temperature trials, including the performance with change in temperature, sample thickness and EMAT-sample lift-off, are presented here.

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Section: Sample Bmentioning

confidence: 94%

Shear wave EMAT thickness measurements of low carbon steel at 450 °C without cooling

Lunn¹,

Potter²,

Dixon³

2017

AIP Conference Proceedings

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show abstract

“…The maximum possible lift-off between the EMAT probe and material depends on the EMAT design, material properties, and the acoustic wave frequency [47]. Studies report that due to the requirement of a reasonable signal-to-noise ratio (SNR), the lift-off is typically restricted to below 3 mm [48].…”

Section: Guided Waves Using Ematsmentioning

confidence: 99%

A feasibility study on different NDT techniques used for testing bond quality in cold roll bonded Al-Sn alloy/steel bimetal strips

2017

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-This paper presents non-destructive testing (NDT) results for the detection of bond defects in aluminiumtin (Al-Sn) alloy/steel bimetal strips. Among all types of bimetal strip that are used in the automotive industry for plain journal engine bearings, Al-Sn alloys cold roll bonded (CRB) onto steel backing is the most common type. The difficulty to evaluate the metallurgical bond between the two dissimilar metals is a major industrial concern, which comprises the risk that bearings fail in the field. Considering the harsh performance requirements, 100% online non-destructive testing would be desirable to significantly reduce the business risk. Nowadays bimetal strip manufacturers still rely on destructive testing through different peel-off tests. This work offers the results from four independent NDT studies, using active thermography, shearography, ultrasound and guided wave electromagnetic acoustic transducers (EMATs) and samples with different artificially implanted defects, to explore the feasibility to qualitatively indicate the occurrence of bond defects. A destructive peel off test was used to correlate the NDT results with known bond quality. The studies were done under laboratory conditions, and in case of ultrasound also online under production conditions. During the ultrasound online test, the requirements that a NDT technique has to fulfil for online inspection of Al-Sn alloy/steel bimetal strip were established. For active thermography, shearography and guided wave EMAT techniques, it was theoretically analysed, if the laboratory test results could be transferred to testing under production conditions. As a result, guided waves using EMATs, among the four tested methods, are best suited for online inspection of Al-Sn alloy/steel bimetal strip. This research was carried out in collaboration with MAHLE Engine Systems UK Ltd., an Al-Sn alloy/steel bimetal strip manufacturer for the automotive industry.

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“…Huang et al [103] applied ANSOFT FEA software to study optimum lift-offs in an EMAT system producing US waves at 250 kHz, designed so that only a magnetostrictive contribution took place in the specimen. They concluded, that the lift-off of a receiver could be very small, but the lift-off of a transmitter should be around 2 mm to ensure the stability of the system.…”

Section: Emats (Electromagnetic Acoustic Transducers)mentioning

confidence: 99%

Finite Element Method Applied in Electromagnetic NDTE: A Review

Augustyniak

Usarek

2016

J Nondestruct Eval

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The paper contains an original comprehensive review of finite element analysis (FEA) applied by researchers to calibrate and improve existing and developing electromagnetic non-destructive testing and evaluation techniques, including but not limited to magnetic flux leakage (MFL), eddy current testing, electromagnetic-acoustic transducers (EMATs). Premium is put on the detection and modelling of magnetic field, as the vast majority of ENDT involves magnetic induction, either as a primary variable MFL or a complementary phenomenon (EC, EMATs). FEA is shown as a fit-for-purpose tool to design, understand and optimise ENDT systems, or a Reference for other modelling algorithms. The review intentionally omits the fundamentals of FEA and detailed principles of NDT. Strain-stress FEA applications in NDT, especially in ultrasonography and hole-drilling methodology, deserve as well a separate study.

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Study on the lift-off effect of EMAT

Cited by 69 publications

References 10 publications

Shear wave EMAT thickness measurements of low carbon steel at 450 °C without cooling

Shear wave EMAT thickness measurements of low carbon steel at 450 °C without cooling

A feasibility study on different NDT techniques used for testing bond quality in cold roll bonded Al-Sn alloy/steel bimetal strips

Finite Element Method Applied in Electromagnetic NDTE: A Review

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