Characterisation of small defects using miniaturised EMAT system

Trushkevych, Oksana; Edwards, R. S.

doi:10.1016/j.ndteint.2019.102140

Cited by 19 publications

(10 citation statements)

References 23 publications

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“…The latter is not necessarily a drawback as the required bandwidth depends on the desired application, and a larger bandwidth can be beneficial in methods that rely on analysing several wavemodes [6] [15] [23]. Reducing the width of the wavefront (designs 2-4) allowed the use of smaller coils with fewer turns, which are expected to have a shorter "dead time" -the time during which the receiving electronics is saturated -thus allowing the generator and detector to be brought closer together, similar to the EMATs reported in [14]. The dead time depends on factors including the sample, transducer impedance, and external shielding, and reducing the coil size reduces the impedance.…”

Section: A Emat Design Considerationsmentioning

confidence: 99%

“…This may be useful in scenarios where sensitivity to a variety of wavemodes is required, such as when using mode conversions as indicative of a defect [6] [15] [24] [23]. Size miniaturisation of detectors can also offer the extra benefit of providing higher spatial resolution when scanning, in particular in the near field, and higher sensitivity to defects with small lateral dimensions [14] [25].…”

Section: A Emat Design Considerationsmentioning

confidence: 99%

“…We have recently produced miniaturised EMATs containing permanent magnets, generating and detecting Rayleigh waves for characterisation of surface-breaking defects on metals [14]. The miniaturisation had the benefits of reducing magnetic drag and overall weight, thus simplifying the inspection process, and in addition improving spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

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Miniaturised SH EMATs for Fast Robotic Screening of Wall Thinning in Steel Plates

et al. 2021

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Electromagnetic acoustic transducers (EMATs) are well suited to generating and detecting a variety of different ultrasonic wavemodes, without the need for couplant, and they can be operated through some coatings. EMATs can be used to generate shear horizontal (SH) waves, which show promise for fast screening of wall thinning and other defects. However, commercial SH-wave EMATs are not suitable for robotic implementation on ferritic steel due to the large magnetic drag force from the magnets. This paper describes the design and characterisation of miniaturised SH guided wave EMATs, which significantly reduce the magnetic drag and enable mounting onto a small crawler robot for sample scanning. The performance of the miniaturised EMATs is characterised and compared to a commercial EMAT. It is shown that signal to noise ratio is reduced, but remains within an acceptable range to use on steel. The bandwidth and directivity are increased, depending on the exact design used. Their ability to detect flat bottomed holes mimicking wall thinning is also tested.

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Section: A Emat Design Considerationsmentioning

confidence: 99%

Section: A Emat Design Considerationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Miniaturised SH EMATs for Fast Robotic Screening of Wall Thinning in Steel Plates

et al. 2021

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“…Rosli et al [27] then detected 1 mm deep and 1 mm wide angled defects by the same method, while Zhou and Xu [14] evidenced 0.1 mm deep normal surface defects by Lamb waves with λ = 6 mm scanning the defect by the source. In two separate analyses, Trushkevych and Edwards [28,29] finally demonstrated that normal surface cracks or thermal fatigue cracks with a depth comprised between 0.5 mm and 2 mm can be evidenced by Rayleigh or Lamb waves, both in coated and uncoated samples. Based on the reported literature review, it is hence derived that no in-depth analysis exists on non-contact detection in air of enhanced Rayleigh waves, and more specifically considering that the defect should be preferably scanned by the receiver rather than the emitter (as suggested by [25,30]).…”

Section: Introductionmentioning

confidence: 99%

Signal Enhancement in Surface Crack Detection with Gas-Coupled Laser Acoustic Detection

et al. 2021

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Ultrasonic signal enhancement resulting from constructive interference between direct Rayleigh waves and same waves reflected by a surface defect is exploited to increase crack identification capabilities of the Gas-Coupled Laser Acoustic Detection (GCLAD) non-contact detection technology. Highlights from simulations are provided regarding the interference phenomenon in the solid and its propagation in air, where GCLAD detection occurs. Experimental campaigns are preliminarily performed on a bar to evidence the effect of cracks on the GCLAD acquired signals. Then, a signal enhancement of +30% is reached on a plate, implying that defects are efficiently scanned by moving the GCLAD in proximity of the discontinuity. Since the GCLAD allows monitoring points of a piece belonging to the same line at once, its translation in one direction is sufficient to perform a two-dimensional scan, entailing reduction of inspection time and simple automation of the interrogation layout compared to other traditional or signal enhancement-based techniques.

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“…For successful implementation with a small crawler robot, however, reducing drag this way is not sufficient, and hence the EMATs used here are miniaturised. Miniaturisation has a second benefit of offering higher spatial resolution when scanning, and higher sensitivity to defects with small lateral dimensions [9].…”

Section: Introductionmentioning

confidence: 99%

Towards Guided Wave Robotic NDT Inspection: EMAT Size Matters

Trushkevych

Dixon

Tabatabaeipour

et al. 2019

2019 IEEE International Ultrasonics Symposium (IUS)

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The first steps towards fast robotic screening of wall thinning in the industrially relevant example of 10mm thick steel plates are reported. Electromagnetic acoustic transducers (EMATs) are used to generate and detect guided shear horizontal wavemodes, as these show promise for this type of inspection. EMATs are miniaturised to reduce magnetic drag on ferritic steels, and are designed to produce SH0 and SH1 wavemodes with 22mm wavelength, which is suitable for testing wall thinning in these samples. Miniaturisation and the resulting reduction of magnetic drag force allows the EMATs to be mounted on a small crawler robot which can then be used to scan the sample / structure.

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Characterisation of small defects using miniaturised EMAT system

Abstract: Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.

Cited by 19 publications

References 23 publications

Miniaturised SH EMATs for Fast Robotic Screening of Wall Thinning in Steel Plates

Miniaturised SH EMATs for Fast Robotic Screening of Wall Thinning in Steel Plates

Signal Enhancement in Surface Crack Detection with Gas-Coupled Laser Acoustic Detection

Towards Guided Wave Robotic NDT Inspection: EMAT Size Matters

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