Electromagnetic ultrasonic tomography of plate defects based on omnidirectional Lamb-wave EMATs

This paper presents the design method of omnidirectional Lamb-wave electromagnetic acoustic transducers (EMATs) for electromagnetic ultrasonic Lamb wave tomography technique. The 360 degrees radiated A0 mode Lamb wave is excited through the selection of the appropriate working point, which not only can realize large range detection of plate structure, but also be more convenient to extract feature of the echo. The travel time between the transmitting and receiving EMATs is measured through using crosshole scanning method. Then slowness image reconstruction is realized by using SIRT (Simultaneous Iterative Reconstruction Technique). The experimental result of imaging of a 1.5 mm deep artificial defect with a diameter of 26 mm in 2mm thick aluminum plate is obtained, according to which the defect can be found.