Optimising ultrasonic wideband Rayleigh wave generation by pulsed electromagnetic coils

Transient ultrasonic Rayleigh wave generation by pulsed electromagnetic coils operating via the Lorentz force mechanism is investigated. Optimal coil design is calculated by considering the entire ultrasonic generation system including the pulse generator, coil shape and size, and the electromagnetic coupling between coil and metal sample. The study is carried out through theoretical modelling and comparison with experimental measurements taken using an 80 MHz bandwidth Michelson laser interferometer as a detector. The time dependent Lorentz force generated by the electromagnetic acoustic transducer (EMAT) is modelled using finite element calculations, and the resultant ultrasonic field is calculated using an efficient numerical algorithm. Excellent correlation is observed between the simulated waveforms and experimental measurements. This demonstrates how the approach reported here will greatly assist in optimising the design of generating EMAT for specific applications.