A Uniform Transversely Polarized Shear Horizontal Electromagnetic Acoustic Transducer for Stress Measurement

Electromagnetic acoustic transducer (EMAT) is preferred in non-destructive stress measurement of metallic materials, because of its non-contact characteristic. However, splitting and overlapping of echo signal can be received when anisotropic material is tested with shear horizontal (SH) wave due to birefringence, which may introduce errors in stress measurement. In this paper, a uniform transversely polarized SH wave EMAT is proposed to reduce the effect of birefringence. Method to evaluate the selectivity for the polarization direction of SH wave is provided, in which a pitch-catch configuration of a proposed EMAT and an omnidirectional polarized EMAT is arranged. Comparisons with traditional transversely polarized EMAT are made on an orthotropic plate. Experimental results show that the newly designed EMAT is uniform transversely polarized as used as the transmitter, and has great selectivity as used as the receiver. Using the proposed EMAT, a stress measurement is performed. The error of stress measurement is within ± 5 MPa.