A type of focused single-mode A0 Lamb wave EMAT for performance improvement

In this paper, a Halbach array periodic permanent magnet (HPPM) electromagnetic acoustic transducer (EMAT) was proposed for generating a stronger and purer A(0) mode Lamb wave (A(0) wave). Compared to conventional periodic permanent magnets (PPM), the HPPM generates a more intense and purer horizontal magnetic field, enhancing A(0) wave amplitude by 28% and suppressing the S-0 mode Lamb wave (S-0 wave) by 32%. Additionally, a focused A(0) wave EMAT (FHPPM-EMAT) with arc structure is proposed. The FHPPM-EMAT demonstrates excellent transduction efficiency and focusing capability. An orthogonal analysis was conducted to evaluate the factors affecting the transduction efficiency of the FHPPM-EMAT. With optimized parameters based on orthogonal analysis, the FHPPM-EMAT achieved a 93% increase in A(0) wave amplitude compared to the HPPM-EMAT. Furthermore, the size of the focal area is characterized by a horizontal focal width (H-d) and a vertical focal width (V-d) of only 36.21 mm and 10.45 mm, respectively.