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Optimization of the bias magnetic field of shear wave EMATs

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Title: Optimization of the bias magnetic field of shear wave EMATs
Authors: Isla, J
Cegla, FB
Item Type: Journal Article
Abstract: The main advantage of electromagnetic acoustic transducers (EMATs) over piezoelectric transducers is that no direct contact with the specimen under test is required. Therefore, EMATs can be used to test through coating layers. However, they produce weaker signals, and hence, their design has to be optimized. This paper focuses on the design of a Lorentz force shear wave EMAT and its application in thickness gaging; special emphasis is placed on the optimization of the design elements that correspond to the bias magnetic field of the EMAT. A configuration that consists of several magnets axisymmetrically arranged around a ferromagnetic core with like poles facing the core was found to give the best results. By using this configuration, magnetic flux densities in excess of 3 T were obtained in the surface of a specimen; the maximum value achieved by a single magnet under similar conditions is roughly 1.2 T. If the diameter of an EMAT ultrasonic aperture is 10 mm, the proposed configuration produces signals roughly 20 dB greater than a single magnet, while for a given overall EMAT volume, signals were greater than 3-6 dB. Linear and radial shear wave polarizations were also compared; a higher mode purity and signal intensity were obtained with the linear polarization.
Issue Date: 1-Aug-2016
Date of Acceptance: 21-Apr-2016
URI: http://hdl.handle.net/10044/1/31275
DOI: 10.1109/TUFFC.2016.2558467
ISSN: 0885-3010
Publisher: Institute of Electrical and Electronics Engineers
Start Page: 1148
End Page: 1160
Journal / Book Title: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control
Volume: 63
Issue: 8
Copyright Statement: This work is licensed under a Creative Commons Attribution 3.0 License. For more information, see http://creativecommons.org/licenses/by/3.0/
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/K033565/1
Keywords: Science & Technology
Engineering, Electrical & Electronic
Electromagnetic-acoustic transducer (EMAT)
non-destructive evaluation (NDE)
ultrasonic transducers
02 Physical Sciences
09 Engineering
Publication Status: Published
Online Publication Date: 2016-04-27
Appears in Collections:Mechanical Engineering
Faculty of Engineering