Characteristic analysis of electromagnetic acoustic transducers for helical shear horizontal wave based on magnetostrictive effect.

The electromagnetic ultrasound detection technology provides an efficient method to inspect the structural health status. For the pipeline structure, the guided ultrasonic wave propagating along the axial direction has been the focus of the current research. However, the helical wave owns the advantage of obtaining the defect information in extra angles and has not been explored sufficiently. In this work, a transducer with a sector configuration is designed for generating helical shear horizontal waves in a pipeline. The magnetostrictive effect is analyzed, and the model is built in the finite element simulation software of COMSOL Multiphysics. The electromagnetic field and displacement distribution are studied. To evaluate the performance of the transducer, the half divergence angle is defined to measure the acoustic beam and evaluate the capacity in generating helical waves. Corresponding experiments are also implemented to analyze the influencing factors in the structural design of the transducer. The results indicate that the pulse cycle affects the half divergence angle slightly. The compromise should be considered when designing the central angle of the transducer because it influences the signal amplitude and further imaging resolution in a contradictory way.