Optimized Design of Electromagnetic Acoustic Sensors for Surface Wave Polarization Measurements

Electromagnetic acoustic transducer (EMAT) has been widely exploited in the field of nondestructive testing due to its advantages of non-contact and designability. In this paper, a surface wave magnetic concentrate type polarization measurement EMAT (magnetic concentrate type polarization measurement, MC-PM-EMAT) is introduced. The sensor utilizes the magnetic field distribution characteristics of two magnetic concentrate type permanent magnet arrays combined with a linear singlecoil structure to enable independent measurements of the in-plane and out-of-plane displacement components of surface wave elliptical polarization. Firstly, the design method of MC-PM-EMAT was proposed, and the magnetic field distribution characteristics of this sensor were analyzed to verify the magnetic flux density enhancement. Secondly, a multi-physics field coupling simulation model of the MCPM-EMAT was established to investigate the measurement capability of the in-plane and out-of-plane displacements of the sensor, and the results show that the proposed MC-PM-EMAT boosts the measurement signals of the in-plane component by a factor of 6. 17 and the out-of-plane component by a factor of 2. 49, compared to that of the conventional type EMAT. Finally, MC-PM-EMAT was developed and the experimental measurement system of surface wave elliptical polarization was built to further experimentally verify the polarization measurement of MC-PM-EMAT. The proposed MC-PM-EMAT significantly improves the polarization measurement capability of surface waves and offers an important sensing test method for the characterization of mechanical properties and non-destructive testing of defects based on polarization characteristics.