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The main disadvantage of electromagnetic acoustic transducers (EMATs) is their inefficiency in generating ultrasound. A new design of Rayleigh-wave EMAT is proposed with improved ultrasonic generation efficiency on non-ferromagnetic materials. The new EMAT's magnet is narrower than the meander-line coil used in the transducer and the coil itself has an uneven distribution of conductors. The principle of the new design is informed by finite element simulations, which show that the EMAT generates Rayleigh waves more efficiently by taking advantage of both horizontal and vertical magnetic fields of the magnet simultaneously. Experimental measurements verify that the maximum amplitude of the ultrasonic signal generated by the new design of EMAT working under a pulse-echo configuration has been enhanced by 90%, when compared to conventional designs. [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]

A three-dimensional model for Rayleigh wave electromagnetic acoustic transducers operating on the Lorentz force mechanism has been established by combining the finite element method and analytical calculation. Rayleigh waves generated by the Lorentz forces due to the static magnetic field and the dynamic magnetic field are calculated. The ratio of wire width to spacing interval (RWWSI) between neighbouring wires is chosen to study the coil parameter influence of Lorentz forces in generating Rayleigh waves. The vibration amplitude of Rayleigh waves due to the dynamic magnetic field is almost 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 the dynamic magnetic field remain invariable when the RWWSI is less than 0.5, and that due to static magnetic field reaches the minimum values and has 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. The accuracy of this method is verified by experiment. [ABSTRACT FROM PUBLISHER]