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Rayleigh wave sound field (normalized)
80
1
0.8
0.6
0
0.4
0.2
-80
0
0
100
200
300
400
500
Y (mm)
Fig. 4.
Calculated Rayleigh wave sound field distribution on aluminum plate surface.
The maximum Rayleigh wave vibration amplitude is normalized.
It was reported that for a spiral coil EMAT, the Lorentz force due to the
dynamic magnetic field
F
d
generates Rayleigh waves more eciently than that
due to the static magnetic field when the p-p amplitude of the excitation current
is about 300 A [11, 12]. However, for a meander-line coil EMAT, this excitation
current is 528.9 A [13]. This difference shows that the EMAT configuration
affects the Lorentz force distribution and also the generated Rayleigh wave dis-
tribution. It is interesting to study the influence of Lorentz forces due to static
and dynamic magnetic fields for commonly used meander-line coil EMATs with
different parameters.
First, the current amplitude is set to be constant. The current amplitude
is 100 A. The relationships between the divergence angle and vibration ampli-
tude of Rayleigh waves and the ratio of wire width to spacing interval between
neighboring wires (RWWSI) is shown in Fig. 5 and Fig. 6.
(a)
(b)
4.8
6.25
4.6
6.2
4.4
4.2
6.15
4.0
6.1
3.8
6.05
3.6
3.4
6.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
RWWSI
RWWSI
Fig. 5.
Relationship between the Rayleigh wave divergence angle and the RWWSI.
Rayleigh waves are generated by Lorentz forces (a) due to the dynamic magnetic field
and (b) due to the static magnetic field respectively.
Fig. 5 indicates that the divergence angle of Rayleigh wave generated by
Lorentz force due to the dynamic magnetic field keeps invariable when the
RWWSI is less than 0.5, whereas that due to the static magnetic field reaches
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