Thring, C. B., Fan, Yichao and Edwards, R. S. (Rachel S.) (2016) Focused Rayleigh wave EMAT for characterisation of surface-breaking defects. NDT & E International, 81 . pp. 20-27. doi:10.1016/j.ndteint.2016.03.002 ISSN 0963-8695.

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Abstract

Developments towards higher resolution and the ability to detect small defects are bringing a step-change in non-destructive testing. This paper presents a new method for increasing resolution, using a focused electromagnetic acoustic transducer (EMAT) optimised to generate Rayleigh waves at 2 MHz. This high frequency allows detection of mm-depth defects, and the focusing allows sizing of much shorter defects than is possible when using standard EMATs. The focusing behaviour and the aperture angle effect are analysed using laser vibrometry and finite element modeling, showing that a reduced aperture shifts the focal point from the designed value and increases the focal depth. The dual-EMAT has excellent signal to noise ratio (up to 30 dB) and has been used in single shot mode to image a variety of surface-breaking defects, including detecting and positioning a pair of real defects in an aluminium billet sample, and a machined defect of 2 mm length, 0.2 mm width, and 1.5 mm depth, giving an upper limit on the defect length of 2.1 +- 0.5 mm. The results can be used to design an EMAT with optimised focal behaviour for defect detection.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Ultrasonics, Rayleigh waves
Journal or Publication Title:	NDT & E International
Publisher:	Elsevier Sci Ltd.
ISSN:	0963-8695
Official Date:	July 2016
Dates:	Date Event July 2016 Published 12 March 2016 Available 11 March 2016 Accepted 16 December 2015 Submitted
Volume:	81
Number of Pages:	8
Page Range:	pp. 20-27
DOI:	10.1016/j.ndteint.2016.03.002
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Date of first compliant deposit:	6 May 2016
Date of first compliant Open Access:	12 March 2017
Funder:	Engineering and Physical Sciences Research Council (EPSRC), University of Warwick

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