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1.0
0.9
Due to static magnetic field
Due to dynamic magnetic field
0.8
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
2
3
4
5
6
7
8
9
10
Amplitude of excitation current (×100A)
Fig. 8. Relationship of Rayleigh wave vibration amplitude with excitation current am-
plitude for different RWWSI. The maximum Rayleigh wave vibration amplitude is
normalized.
The Lorentz force acting region is decomposed into many point forces, and
each point force has contribution to Rayleigh waves generated on the aluminum
plate. With the increase of the RWWSI, not only the Lorentz force amplitude
changes but also the force distribution changes. The interference between each
point force components differs. This may cause the Rayleigh wave vibration
amplitude is proportional to the reciprocal but not the inverse square of the
RWWSI. When the RWWSI is less than 0.5, the acting area of the Lorentz force
due to the dynamic magnetic field hardly changes, so the divergence angles keep
invariable. However, the acting area becomes larger when the RWWSI is larger
than 0.5, which causes the divergence angle becomes larger. In contrast, the
acting areas of the Lorentz force due to the static magnetic field changes linearly
with the increase of the RWWSI. When the RWWSI is 0.5, the interference of
each point Lorentz force component is most obvious and generates Rayleigh
waves with the minimum divergence angle.
Rayleigh waves generated by the 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 the Lorentz force due to the static
magnetic field, the RWWSI is recommended to be 0.5.
As has mentioned, the RWWSI has different influences on the Rayleigh waves
generated by Lorentz forces due to dynamic and static magnetic fields respectively.
So it is assumed the critical current mentioned in [13] will also be affected by the
RWWSI. The relationship between the Rayleigh wave vibration amplitude due to
static and dynamic magnetic fields respectively with the excitation current ampli-
tude are calculated as shown in Fig. 8. The critical current varies with the RWWSI
and changes sharply when the RWWSI increases. It is proved that ignoring the
contribution of the dynamic magnetic field is problematic [11-13]. The divergence
angles of Rayleigh waves keep invariable when the RWWSI changes.
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