Influence of Coil Parameters on Rayleigh Waves Excited by Meander-Line Coil EMATs - Intelligent Computing for Sustainable Energy and Environment - page 95

In early researches, the influence of the dynamic magnetic field generated by
the excitation current was ignored. With the development of electronics, the
excitation current becomes larger and larger, and the dynamic magnetic field
plays an unignorable role in generating ultrasounds. Some researchers have es-
tablished Rayleigh wave EMAT models considering the influence of the dynamic
magnetic field [11-13]. Two Lorentz forces are calculated, including the Lorentz
force due to the static magnetic field and the Lorentz force due to the dynamic
magnetic field. The relationship between Rayleigh wave displacements generated
by these two Lorentz forces individually and the excitation current are calculated
for spiral coil EMATs [11, 12] and meander-line coil EMATs [13] operating on
the Lorentz force mechanism.
In industrial application, EMATs consisting of a meander-line coil and a
static magnetic field are widely applied to generate and detect Rayleigh waves.
Meander-line coils are designed with different lengths, widths and spacing inter-
vals. These parameters will affect Rayleigh waves generated by these two Lorentz
forces.
In this paper, finite element method and analytical solutions are combined to
calculate Rayleigh waves generated by meander-line coil EMATs working on the
Lorentz force mechanism. Based on this method, the influence of coil parameters
on generating Rayleigh waves are compared and analyzed.

2 Modeling Method

Electromagnetic acoustic transducers mainly consist of three parts: a coil, a
static magnetic field and a sample under test. The working process of an EMAT
operating on Lorentz force mechanism is illustrated in Fig.1.

Z

Straight wire

B s

J 0

X

B d
F s
F d

J E

Y

Aluminum plate

Fig. 1. Lorentz force mechanism in aluminum plate

I 0 passes through the coil, the current density
J 0 will generate a dynamic magnetic field

When an alternating current

B d in the surrounding air and the
aluminum plate, and the dynamic magnetic field will induce an eddy current J E