Experimental-numerical Determination of the Lorentz and Magnetostriction Mechanism in the Periodic Permanent Magnet Electromagnetic Acoustic Transducer on Steel

This thesis determines the relative strength of magnetostriction to Lorentz within the Periodic Permanent Magnet Electromagnetic Acoustic Transducer (PPM EMAT) on steel, which is designed to induce only the Lorentz mechanism. As both mechanisms operate at the same frequency and wavelength, the ratio between Lorentz and magnetostriction is determined through an experimental-numerical method. Another EMAT, which only induces magnetostriction, is constructed to operate at the same wavelength and frequency. In addition, it replicates the magnetic conditions underneath the PPM EMAT that cause magnetostriction. A series of experiments are conducted with both EMATs in a pitch-catch configuration, finding that magnetostriction is significant only at the transmitter. A magnetostriction model is developed specifically for the PPM EMAT, and 3D Finite Element simulations predict EMAT performance. It is found that magnetostriction reduces the output of the PPM EMAT transmitter output by an average of 29% across multiple input current tests.M.A.S