Direction-enhanced guided wave transducer based on pulse compression technique

Ultrasonic guided waves are widely employed for structural health monitoring (SHM) as well as in nondestructive testing and evaluation (NDT&E). The 0th order shear horizontal (SH0) guided wave, known for its simple vibration mode and non-dispersive characteristics, simplifies the interpretation of detection signals. However, traditional transducers that generate and receive the SH0 guided wave bidirectionally pose challenges for defect localization. This paper introduces an electromagnetic acoustic transducer (EMAT) based on the pulse compression technique for directional enhancement. The direction-enhanced EMAT consists of a linear frequency modulation (LFM) excitation signal and periodic permanent magnets (PPMs) arranged in variable spacings and widths. An analytical model is developed to predict the received signals and analyze the pulse compression mechanism of the PPM EMAT. During the transmitting and receiving process, the PPMs align the phase of the broadband excitation signal to obtain a compressed and enhanced received signal. Additionally, the enhanced side can be controlled using different LFM excitation signals. Finally, the directional enhancement is validated through finite element simulations and experimental results. The proposed direction-enhanced guided wave transducer and its design methodology demonstrate significant potential for SHM and NDT&E in plates, shells, and pipelines.