Numerical Design Optimization of an EMAT for A0 Lamb Wave Generation in Steel Plates

An electromagnetic acoustic transducer (EMAT) for A0 Lamb wave generation on steel plates is developed to operate at 0.50 MHz-mm. A key objective of the development is to maximize the excitation and reception of the A0 mode, while minimizing those of the S0 mode. The chosen EMAT design consists of an induction coil and a permanent magnet. A finite element (FE) model of the EMAT is developed, coupling the electromagnetic and elastodynamic phenomena. An optimization process using a genetic algorithm is implemented, employing the magnet diameter and liftoff distance from the plate as design parameters and using the FE model to calculate the fitness. The optimal design suggested by the optimization process is physically implemented and the experimental measurements are compared to the FE simulation results. In a further step, the variations of the design parameters are studied numerically and the proposed EMAT design exhibits a robust behavior to small changes of the design parameters.