Multi-angle steering of a meander-line coil EMAT

EMATs are capable of both transmitting and receiving ultrasonic waves within ferromagnetic and conductive materials. Meander-Line Coil (MLC) EMATs can transmit not only Rayleigh waves across the material's surface but also compression and shear waves at an angle into the material. The frequency of the transmission signal controls the propagation angle of the shear waves, and this paper establishes the simulated and experimental results for an MLC EMAT's beam directivity across desired steering angles of 15-90°. These results show that: a maximum magnitude occurred at the 31° steering angle; a steering limit at the 48° steering angle; and the maximum reception angle attained was at 61.1°. The sum of two steering angles' transmission signals showed the EMAT capable of generating two distinct shear wave beams at different propagation angles simultaneously. Further simulated modelling of the EMAT in a Pulse-Echo (PE) setup confirmed not only that the two beams could detect defects present in the material, but that the detecting beam could be identified by filtering of the returning waves.