Abstract
In order to improve the transduction efficiency of electromagnetic acoustic transducer (EMAT) for steel plates inspection, the constitutive equation of magnetostrictive material was theoretically derived and simplified while the magnetostrictive force is parallel to the material surface. Based on the multiphysics field FEM, the effects of such excitation parameters as current, frequency, and pulse number in AC coils on magnetostrictive strain were mainly simulated, and the influence of the coil with different winding shapes on magnetostrictive strain was also analyzed. The simulation and experimental results indicate that magnetostrictive strain increases with a continuously increasing excitation current density, but it decreases with the increase of the frequency and pulse number of AC currents. Moreover, on condition that loop length and AC currents are held constant, spiral type coils have higher transduction efficiency than homocentric squares and figure-of-eight coils.
Highlights
Since the electromagnetic acoustic transducer (EMAT) guided-wave technique can overcome such limitations as low-efficiency and high-cost of some conventional NDT techniques and realize the noncontact, long distance, and quick inspection, it shows some significant advantages for large-scale components inspection
[2] and analyzed the influences of alternating magnetic field generated by AC current on the precision of EMAT [3, 4]
The EMAT transduction mechanism is different with different materials; for example, the approach only relies on Lorentz force for nonferromagnetic materials, and magnetostrictive force plays leading role in generation of electromagnetic acoustic wave for ferromagnetic materials
Summary
Since the EMAT guided-wave technique can overcome such limitations as low-efficiency and high-cost of some conventional NDT techniques and realize the noncontact, long distance, and quick inspection, it shows some significant advantages for large-scale components inspection. By coupling the alternating magnetic field in AC coils and the bias magnetic field provided by permanent magnets, an ultrasonic guided-wave is generated in the steel plate via the magnetostrictive effect. Jian et al studied the liftoff effect of EMAT by establishing coil equivalent circuit [2] and analyzed the influences of alternating magnetic field generated by AC current on the precision of EMAT [3, 4]. Yang et al simulated generation mechanism of the electromagnetic acoustic wave in aluminum plates and analyzed its propagation characteristics [5]. With the high-efficiency numerical method being used widely, the FEM based on multiphysics field coupling has become a very useful technique to simulate the magnetostrictive effect. The simulation results are verified by experiments with the help of a self-developed EMAT guided-wave system
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