EMAT phased array: a feasibility study of surface crack detection
File(s)
Published version
Author(s)
Isla, J
Cegla, FB
Type
Journal Article
Abstract
Electromagnetic-acoustic transducers (EMATs) consist of a magnet and a coil. They are advantageous in some non-destructive evaluation (NDE) applications because no direct contact with the specimen is needed to send and receive ultrasonic waves. However, EMATs commonly require excitation peak powers greater than 1 kW and therefore the driving electronics and the EMAT coils have to be bulky. This has hindered the development of EMAT phased arrays with characteristics similar to those of conventional piezoelectric phased arrays. Phased arrays are widely used in NDE because they offer superior defect characterization in comparison to single-element transducers. In this paper, we report a series of novel techniques and design elements that make it possible to construct an EMAT phased array that performs similarly to conventional piezoelectric arrays used in NDE. One of the key enabling features is the use of coded excitation to reduce the excitation peak power to less than 4.8 W (24 Vpp and 200 mA) so that racetrack coils with dimensions can be employed. Moreover, these racetrack coils are laid out along their shortest dimension so that 1/3 of their area is overlapped. This helps to reduce the crosstalk between the coils, i.e., the array elements, to less than −15 dB. We show that an 8-element EMAT phased array operating at a central frequency of 1 MHz can be used to detect defects which have a width and a depth of 0.2 and 0.8 mm respectively and are located on the surface opposite to the array.
Date Issued
2017-07-01
Date Acceptance
2017-02-10
Citation
Ultrasonics, 2017, 78 (1), pp.1-9
ISSN
0041-624X
Publisher
Elsevier
Start Page
1
End Page
9
Journal / Book Title
Ultrasonics
Volume
78
Issue
1
Copyright Statement
© 2017 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://www.sciencedirect.com/science/article/pii/S0041624X16302785
Grant Number
EP/K033565/1
Subjects
Science & Technology
Technology
Life Sciences & Biomedicine
Acoustics
Radiology, Nuclear Medicine & Medical Imaging
EMAT
Ultrasonic arrays
Low-SNR
Coded sequences
Pulse-compression
NDE
Material inspection
ELECTROMAGNETIC ACOUSTIC TRANSDUCERS
ULTRASONIC ARRAY
NONDESTRUCTIVE EVALUATION
RAYLEIGH-WAVE
FULL-MATRIX
PROPAGATION
IMPROVEMENT
INSPECTION
DEFECTS
Coded sequences
EMAT
Low-SNR
Material inspection
NDE
Pulse-compression
Ultrasonic arrays
0203 Classical Physics
0912 Materials Engineering
0913 Mechanical Engineering
Acoustics
Publication Status
Published
Date Publish Online
2017-02-14