Application of modified complementary-coded excitation method in EMAT detection

Traditional binary complementary sequences generally depend on two encoding and decoding cycles to realize pulse compression, which tends to introduce detection errors and limit detection speed. To address these limitations, this paper proposes a single-coded excitation method based on the complementary A code, replacing the conventional dual excitation of A and B codes. The method was evaluated using a finite element model of a spiral coil electromagnetic acoustic transducer (EMAT) and thickness measurement experiments on ZG40Cr steel, with 16-bit Golay and 16-bit G-LFM signals employed as excitations. Simulations and experimental results demonstrated that the single-code excitation approach overcomes the drawbacks of dual excitation while maintaining a comparable signal-to-noise ratio (SNR) gain. Moreover, the pulse compression performance of Tone-burst, 13-bit Barker, 16-bit Golay, 20-bit complementary, and combined coded signals were compared under varying EMAT lift-offs. The results indicated that the proposed method achieves effective decoding under various noise levels, with the 16-bit Golay code yielding the highest SNR. It was also observed that the combined coded signal reduces the main lobe width by approximately 50% compared to phase-coded signals.