Design of Permanent Magnet Electromagnetic Acoustic-Wave Transducers (EMATs)

Electromagnetic acoustic-wave transducers (EMATs) provide a means of generating and detecting shear and compressional acoustic waves of known amplitude in conductors by electromagnetic instead of mechanical coupling to the material under study. An EMAT consists of a coil to generate eddy currents in the conductor and a magnetic field to provide coupling between the eddy currents and the metal lattice. Most work to date has been on EMATs utilizing either large permanent magnets or electromagnets. Here we describe a simple but very practical model for a rare-earth cobalt permanent magnet EMAT. This model is analyzed in detail and compared with measurements of the performance of a compact (250 gram) EMAT.