Relative ability of wedge coupled piezoelectric and meander coil EMAT probes to generate single mode Lamb waves
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Published version
Author(s)
Cawley, P
Khalili, Pouyan
Type
Journal Article
Abstract
Ultrasonic guided waves are used extensively when checking for defects in petrochemical and other industries and are mostly generated using piezoelectric transducers on an angled wedge or EMATs in different configurations. Low frequency inspection allows for long distance propagation but it is best suited for detecting relatively large defects, while at higher frequencies, the presence of multiple wave modes limit defect detectability, so achieving practical single Lamb mode excitation via careful transduction is very beneficial. This paper investigates the relative ability of angled piezoelectric and meander coil EMAT probes to produce single mode transduction in the medium (~1 to 5 MHz-mm) and high (> 5 MHz-mm) frequency-thickness regions of the dispersion curves. The nature of each transducer is studied analytically by simulating the corresponding surface forces, followed by the use of a Fourier transform in time and space (2-D FFT) to highlight the excitation region in wavenumber-frequency space. With angled wedge excitation there is a linear relationship between the excitation frequency and the wavenumber which means the excitation tends to track typical dispersion curves, allowing for easier pure mode generation. In contrast, the EMAT controls frequency and wavenumber separately which makes it more difficult to generate a pure mode when dispersion curves are close together; however, by narrowing the frequency bandwidth via a large number of cycles in the excitation signal, pure mode generation via an EMAT was shown to be possible even in areas of closely spaced modes. As example cases, analytical results, backed up by experiments, showed that signals dominated by the A0 mode at 1.5 MHz-mm and also the A1 mode at 18 MHz-mm can be generated with both angled piezoelectric and EMAT probes.
Date Issued
2018-04-01
Date Acceptance
2018-01-27
Citation
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2018, 65 (4), pp.648-656
ISSN
0885-3010
Publisher
Institute of Electrical and Electronics Engineers
Start Page
648
End Page
656
Journal / Book Title
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control
Volume
65
Issue
4
Copyright Statement
© 2018 The Author(s). This work is licensed under a Creative Commons Attribution 3.0 License. For more information, see http://creativecommons.org/licenses/by/3.0/
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
Grant Number
EP/J01284X/1
EP/L022125/1
Subjects
Science & Technology
Technology
Acoustics
Engineering, Electrical & Electronic
Engineering
Electromagnetic acoustic transducer (EMAT)
fast Fourier transform (FFT)
guided waves
higher order mode cluster (HOMC)
modal decomposition
mode selectivity
INTERDIGITAL PVDF TRANSDUCERS
AXISYMMETRICAL GUIDED-WAVES
MAGNETOSTRICTIVE TRANSDUCER
COMB TRANSDUCERS
SHM APPLICATIONS
PIPE INSPECTION
A(0) MODE
DESIGN
EXCITATION
DEFECTS
02 Physical Sciences
09 Engineering
Publication Status
Published
Date Publish Online
2018-02-02