Influence of Coil Parameters on Rayleigh Waves Excited by Meander-Line Coil EMATs - Intelligent Computing for Sustainable Energy and Environment - page 94

Influence of Coil Parameters on Rayleigh Waves
Excited by Meander-Line Coil EMATs
Shujuan Wang, Zhichao Li, Lei Kang, and Guofu Zhai
School of Electrical Engineering and Automation, Harbin Institute of Technology,
150001, Harbin, P.R. China
[e-mail], [e-mail]
Abstract. A 3-D model for Rayleigh wave EMATs operating on the
Lorentz force mechanism has been established. Rayleigh waves genera-
ted by two Lorentz forces are calculated respectively. The ratio of wire
width to spacing interval between neighboring wires (RWWSI) is chosen
to study the coil parameter influence of Lorentz forces. The vibration
amplitude of Rayleigh waves due to the dynamic magnetic field is al-
most proportional to the reciprocal of the RWWSI, whereas that due
to the static magnetic field decreases slowly with the increase of the
RWWSI. The divergence angles of Rayleigh waves due to dynamic mag-
netic field keep invariable when the RWWSI is less than 0.5, and that
due to static magnetic field reach the minimum values and have better
detectability when the RWWSI is 0.5. The critical excitation current,
at which Rayleigh waves due to static and dynamic magnetic fields are
equal, changes sharply when the RWWSI differs.
Keywords: Rayleigh wave, EMATs, Lorentz forces, RWWSI.
1 Introduction
In the field of non-destructive detection and non-destructive evaluation, Rayleigh
waves are widely applied in detection of surface and sub-surface slots and defects
[1-4]. There are various non-contact technologies for generating and detecting
Rayleigh waves and the frequently used are lasers and electromagnetic acoustic
transducers (EMATs) [1-4]. Independence of couplant opens up a wide variety
of applications for EMATs [5], such as inspections at high speed or at high tem-
peratures, which are unavailable to conventional piezoelectric transducer (PT)
techniques.
The main disadvantage of EMATs is their low eciency of generation and
detection. Comparing with PT techniques, electromagnetic acoustic signals are
extremely weak. In [1, 2], EMATs are designed as detectors of ultrasound be-
cause of their better detection performance than generation. Several theoretical
models and experimental work have been done to study the coupling mechanism
of EMATs [6-13]. Some work has been published on optimizing the design of
EMATs for Rayleigh wave generation [11-13].