Development of an array pickup electromagnetic acoustic transducer and application to surface wave visualization

Abstract

Visualization of surface wave based on signal and imaging processing schemes is an efficient way to enhance the detectability of ultrasonic testing for inspection of surface or near surface small defect in layered structures such as the thermal barrier coating (TBC) system. A full wave field measurement is necessary to get information for visualization of the ultrasonic wave. In this paper, a non-contact, array pickup electromagnetic acoustic transducer (EMAT) with 32 receiving coils and a phased array EMAT system are developed for efficient measurement of full information of surface wave field. Based on the multiple channel EMAT signals at different scanning position, a dynamic visualization algorithm is developed to image the propagation, reflection and scattering wave caused by defect and structure edges. The validities of the array pickup EMAT and the dynamic visualization algorithm are demonstrated by using both simulated and measured surface wave signals for a prototype array EMAT and an aluminum plate with small hole defect.