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It is usually considered that the wavelength of guided waves propagating in plates is equal to the double spacing interval of the meander-line coil of electromagnetic acoustic transducers (EMATs). However, the actual value of the wavelength might deviate from the double spacing. This paper takes Shear Horizontal (SH) waves for instance to study the relationship between the wavelength deviation and the parameters of EMATs. It is shown that the wavelength deviation occurs when the operating point of EMATs does not locate on the dispersion curves of a certain SH mode. A wavelength measurement method is proposed to evaluate the deviation by the time-frequency analysis of detected wave signals. Experiments are set up to study the phenomenon of wavelength deviation and verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Currently, the finite element method (FEM) and analytical calculation are widely employed for the modeling of electromagnetic acoustic transducers (EMATs). However, it takes long time for finite element calculation. Previous analytical models for bulk wave EMATs are generally considered separately and incompletely, and expressions of radiated wave fields contain infinite integrations and multiple singular points, which result in complex numerical computation. A complete model containing the Lorentz force and radiated wave field calculation for the EMAT with a spiral coil and a NdFeB permanent magnet is established. By introducing a current loop instead of the permanent magnet and adopting the truncated region eigenfunction expansion (TREE) method, the distributions of static and dynamic magnetic fields and their generated Lorentz forces are calculated. A series expansion method is proposed for the computation of radiated wave fields, which replaces the integration by series operation and avoids the solutions of singular points effectively. The Lorentz forces and radiated wave fields of a typical transducer are computed. The validity of the model is verified by FEM and experiments. Their good agreements verify the accuracy and validity of the model. [ABSTRACT FROM AUTHOR]