Affiliations: [a] Institute for Nondestructive Testing and Mechatronics
Engineering, Beihang University, Beijing 100191, China | [b] EddySun (XiaMen) Electronic Co. Ltd., Xiamen 361004,
China
Abstract: The conductive or ferromagnetic material with coating layer can be
tested by electromagnetic acoustic transducer (EMAT) without pre-treatment. The
electro-acoustic converting occurred on the surface of the specimens is mainly
concentrated within the skin depth of the eddy current. Thus, the
electromagnetic property of the material surface has great influence on the
efficiency of EMAT. The eddy current densities induced in the coating of
specimens and Lorentz force are calculated with finite element software ANSYS
when EMAT is applied to the 20 steel-based specimens coated with different
electrical conductivity materials. With shear wave EMAT, the specimens are
tested and the relationship between the amplitude of the first echo wave signal
and electrical conductivity of the coating is analysed. The theoretical
analysis and experimental results show that under the fixed excitation
condition, the higher the electrical conductivity of the coating material, the
larger the induced eddy current density and Lorentz force are; the increase of
the electrical conductivity of the coating is beneficial to the electromagnetic
acoustic excitation and the acquisition of higher voltage amplitudes of the
echo waves signals.
