Generation of Rayleigh waves using a phased electromagnetic acoustic transducer (EMAT) array

This work presents a phased electromagnetic acoustic transducer (EMAT) array method for enhanced Rayleigh wave generation. The EMAT array was formed of a 1-D linear coil array, where each coil was treated as a separate ultrasonic element for generation, with each having individual driving control. By delaying the coils sequentially, constructive interference of Rayleigh waves can be obtained to give an increased signal to noise ratio. By controlling the delays further, the array can be optimised to generate a chosen wavelength, making the system more adaptable in practical use. The lift-off performance of the phased array system is also introduced, explaining a shift in frequency observed as lift-off of the EMAT above the sample was increased. The frequency shift implies that compensation is needed in practical use to ensure that a correct frequency is obtained.