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The effect of EMAT coil geometry on the Rayleigh wave frequency behaviour

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Thring, Claire B., Hill, Stephen, Dixon, Steve M. and Edwards, R. S. (Rachel S.) (2019) The effect of EMAT coil geometry on the Rayleigh wave frequency behaviour. Ultrasonics, 99 . 105945. doi:10.1016/j.ultras.2019.06.007

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Official URL: https://doi.org/10.1016/j.ultras.2019.06.007

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Abstract

Understanding of optimal signal generation and frequency content for electromagnetic acoustic transducers (EMATs) is key to improving their design and signal to noise ratio. Linear and meander coil designs are fairly well understood, but other designs such as racetrack or focused coils have recently been proposed. Multiple transmission racetrack coil EMATs, with focused and unfocused designs, were constructed. The optimum driving frequency for maximum detected signal was found to range between 1.1 and 1.4 MHz on aluminium for a 1.5 mm width coil. A simple analytical model based on the instantaneous velocity of a wave predicts a maximum signal at 1.44 MHz. Modelling the detection coil as a spatial square wave agrees with this, and predicts a general relation of f =0.761v/L between the optimum frequency f , the wave velocity v, and the coil width L. A time domain model of the detection coil predicts a 1.4-1.5 MHz peak for continuous wave excitation, with a frequency that decreases as the length of the wavepacket is decreased, consistent with the experimental data. Linear coil modelling using the same technique is shown to be consistent with previous work, with improving detection at lower wave frequencies, and signal minima at every integer multiple of the wavelength. Finite Element Analysis (FEA) is used to model the effects of the spatial width of the racetrack generation coil and focused geometry, and no significant difference is found between the focused and the unfocused EMAT response. This highlights the importance of designing the EMAT coil for the correct lift-off and desired frequency of operation. [Abstract copyright: Copyright © 2019 Elsevier B.V. All rights reserved.]

Item Type: Journal Article
Subjects: Q Science > QC Physics
Q Science > QE Geology
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Faculty of Science > Physics
SWORD Depositor: Library Publications Router
Library of Congress Subject Headings (LCSH): Electroacoustic transducers , Rayleigh waves , Acoustic emission testing, Nondestructive testing, Magnetic testing , Frequencies of oscillating systems
Journal or Publication Title: Ultrasonics
Publisher: Elsevier Science BV
ISSN: 0041-624X
Official Date: November 2019
Dates:
DateEvent
November 2019Published
12 June 2019Available
10 June 2019Accepted
Volume: 99
Article Number: 105945
DOI: 10.1016/j.ultras.2019.06.007
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
UNSPECIFIED[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
UNSPECIFIEDUniversity of Warwickhttp://dx.doi.org/10.13039/501100000741

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