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5Conluon
To study the coil parameter influence on Rayleigh waves generated by meander-
line coil EMATs, 3-D models have been established by combination of FEM
and analytical solutions. Lorentz force distributions due to static and dynamic
magnetic fields can be calculated respectively by FEM. Rayleigh waves generated
by the Lorentz forces are obtained by analytical solutions.
The Rayleigh wave vibration amplitude and divergence angle have close rela-
tionship with the RWWSI. The vibration amplitude of Rayleigh waves generated
by Lorentz forces due to the dynamic magnetic field is almost proportional to
the reciprocal of the RWWSI, whereas that due to the static magnetic field de-
creases slowly when the RWWSI increases. The divergence angle of Rayleigh
waves generated by Lorentz forces due to the dynamic magnetic field keeps in-
variable when the RWWSI is less than 0.5, and that due to the static magnetic
field reach a minimum value when the RWWSI is 0.5.
Rayleigh waves generated by Lorentz force due to the dynamic magnetic field
have larger energy and better directivity when the RWWSI is smaller. Whereas
for Rayleigh waves generated by Lorentz force due to the static magnetic field,
theRWWSIisrecommendedtobe0.5.
The critical excitation current, at which Rayleigh wave displacements gener-
ated by Lorentz forces due to static and dynamic magnetic fields respectively
are equal, changes sharply with the increase of the RWWSI. When the RWWSI
is small, Lorentz forces due to the dynamic magnetic field will be more ecient
in generating Rayleigh waves at a low excitation current.
References
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Acoustic Transducer Signals From Rayleigh Wave Interaction at Surface Features.
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Scattered at a Surface Crack. Ultrasonics 44, e1131-e1134 (2006)
5. Hirao, M., Ogi, H.: EMATs for Science and Industry: Noncontacting Ultrasonic
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Rayleigh and Lamb Waves. IEEE Trans. Sonics and Ultrasonics SU-20(4), 340-346
(1973)
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servation Law Description of the Electromagnetic Acoustic Transduction Process.
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(2001)
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