Development of an Integrated EMAT With Longitudinal and Orthogonal Polarized Shear Waves for Plane Stress Measurement

The combined use of longitudinal and shear waves is an effective method for measuring plane stress. However, two piezoelectric ultrasound transducers are used separately in existing measurement methods, which affects the measurement efficiency and accuracy. The existing integrated electromagnetic acoustic transducer (EMAT) with longitudinal and shear waves is limited by the multidirectional polarization direction of shear waves, as well as the signal-to-noise ratio (SNR) of echoes, and cannot effectively measure plane stress. Hence, an integrated EMAT with longitudinal and orthogonal polarized shear waves is developed for measuring plane stress. An orthogonal Halbach array magnet is designed, and the vertical and horizontal magnetic fields with high intensity are generated in distinct designated areas. Compared with a single magnet, the absolute values of vertical and horizontal magnetic flux densities (MFDs) increase by 113% and 76%, respectively. The influence of four coils on wave is analyzed. Finally, an integrated EMAT with high-purity longitudinal and orthogonal polarized shear waves is developed. The SNR of ultrasonic waves has significantly increased compared with the conventional EMAT. Besides, a good linear relationship between stress and propagation velocities is obtained, which validates the advantages of the developed EMAT for stress measurement.