5. Ultrasonic Transducers
A Green's function calculation of the far field radiation patterns of EMAT's is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green's function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT's and horizontally polarized shear waves as radiated by the latter.
Pardee, William J. and Thompson, R. B., "Half-Space Radiation by EMAT's" (1980). Proceedings of the DARPA/AFML Review of Progress in Quantitative NDE, July 1978–September 1979. 26.