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Enhancement of the unidirectional radiation pattern of shear horizontal ultrasonic waves generated by side-shifted periodic permanent magnets electromagnetic acoustic transducers with multiple rows of magnets

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Martinho, Lucas M., Kubrusly, Alan C., Kang, Lei and Dixon, Steve M. (2022) Enhancement of the unidirectional radiation pattern of shear horizontal ultrasonic waves generated by side-shifted periodic permanent magnets electromagnetic acoustic transducers with multiple rows of magnets. IEEE Sensors Journal, 22 (8). pp. 7637-7644. doi:10.1109/JSEN.2022.3156849 ISSN 1530-437X.

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Official URL: http://dx.doi.org/10.1109/JSEN.2022.3156849

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Abstract

Shear horizontal (SH) guided waves are widely used in non-destructive evaluation and can be generated by permanent magnet electromagnetic acoustic transducer (PPM EMATs). PPM EMATs generate SH waves that propagate either forwards and backwards. This is often an undesirable characteristic. Unidirectional generation can be achieved by the interference mechanism produced by two independent sources. This, however, is non-feasible for the conventional PPM EMATs due to the arrangement of PPM array and racetrack coil. Recently, we presented a design of an SH EMAT with side-shifted PPM arrays that generates SH waves nominally in a single direction. Due to the shift of the produced wavefronts from each array, that design produced side-lobes in the backward semi-plane. In this paper, we enhance the unidirectional generation of SH waves with side-shifted PPM EMATs by evaluating the effect of the separation between individual arrays as well as the number of rows of magnets in each array. An analytical model is used to calculate the radiation pattern. The amplitude of the backward side-lobes decreases either with increasing the number of magnets rows or decreasing the lateral gap between rows. This behaviour is explained by the amount of wavefront misalignment introduced by each design. Increasing the number of magnets rows also increases the directivity and the energy of the forward generated waves. Twelve different configurations were fabricated, with a reasonably short wavelength of 12 mm, and experimentally evaluated, agreeing with the theoretically calculated radiation pattern. The magnitude of the backward side-lobes was roughly halved when compared with the original design.

Item Type: Journal Article
Divisions: Faculty of Science, Engineering and Medicine > Science > Physics
Journal or Publication Title: IEEE Sensors Journal
Publisher: Institute of Electrical and Electronic Engineers
ISSN: 1530-437X
Official Date: 15 April 2022
Dates:
DateEvent
15 April 2022Published
3 March 2022Available
1 March 2022Accepted
Volume: 22
Number: 8
Page Range: pp. 7637-7644
DOI: 10.1109/JSEN.2022.3156849
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access

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