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Building 3-D physical
whole model
Building 3-D physical
DMF model
Mesh
discretization
Mesh
discretization
Building 3-D finite element
whole model
Building 3-D finite element
DMF model
Finite element
calculation
Finite element
calculation
Distribution of composite
force
Lorentz force distribution
due to dynamic field
f
L
f
d
Lorentz force distribution
due to static field
Analytical
calculation
f
s
Analytical
calculation
Sound field of Rayleith
wave due to
f
d
Sound field of Rayleigh
wave due to
f
s
Fig. 2.
3-D modeling process of Rayleigh wave EMATs
The Lorentz force distribution depends on the EMAT configuration, including
the coil and the magnet configuration. Some parameters of the coil affects the
Lorentz force distribution, such as wire number
N
C
,width
W
C
,length
L
C
and
thickness
T
C
, spacing interval between wires
a
, lift-off distance between the coil
and the aluminum plate
G
, and excitation current amplitude
A
I
. For meander-
line coil EMATs, cuboid magnets are mainly adopted to generate Rayleigh waves,
so the magnet width
W
M
,length
L
M
and thickness
T
M
should be considered.
Structural parameters of meander-line coil EMATs are illustrated in Fig. 3.
In early research [18], we found that the wire width is the key parameter af-
fecting Rayleigh waves generated by meander-line coil EMATs. The parameter
values of meander-line coil EMAT are chosen according to the practical appli-
cation, and the working frequency is 500 kHz. In aluminum, the Rayleigh wave
velocity is about 2930 m/s, so the spacing intervals between neighboring wires
are 2.93 mm. The coil has 12 wires and each wire has a length of 35 mm, and a
thickness of 0.035 mm. The lift-off distance between the coil and the aluminum
plate is 0.1 mm. Only the part of aluminum plate where the electrical-acoustic
energy conversion takes place is modeled and its size is 50 mm
×
50 mm
×
1.58
10
−
8
mm. The resistivity of the aluminum is 2
.
6
m. The mostly used Nd-Fe-B
is taken as permanent magnet, whose remnant magnetism is 1.21 T.
×
Ω
·
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