Effect of static bias magnetic field on electromagnetic acoustic transducer sensitivity

Static bias magnetic field is the main factor which affects the electro-acoustic converting efficiency of electromagnetic acoustic transducer(EMAT). To improve the sensitivity of the transducer, magnetic induction intensity produced from permanent magnet in EMAT is calculated by ANSYS and the distribution of eddy current density on the permanent magnet surface is obtained to guide the optimization of EMAT with experimentation. The results show that the received signal amplitude increases, as well as the disturbance of coil when the space between permanent magnet and coil decreases; an optimum value is obtained when the space has a proper value. The sensitivity of EMAT is affected by the thickness of permanent magnet, with the increasing of thickness, the magnetic induction intensity increases as well but the gradient gradually becomes small. The application of poly magnetic plate contributes to concentrating the magnetic induction intensity and improving the signal-to-noise ratio of echo signal.