Efficient detection of delamination in multilayered structures using ultrasonic guided wave EMATs

This paper presents an efficient method for the detection of delamination using a combined technology of ultrasonic guided wave and electromagnetic acoustic transducer (EMAT). The material for inspection studied in this paper is a three-layered brass/copper/brass metal composite for coin stocks. We first observed a cyclic behavior of wave sensitivity to delamination width in the experiment. This observation is then confirmed with finite element simulation. We found out that the cyclic behavior is related to the phase velocity of the converted wave modes in the two subsystems after delamination. To compensate for the cyclic behavior, two wave modes are used in an industrial inspection system to ensure effective detection of delamination in the composite sample. The inspection speed achieved with this EMAT inspection system is 1.8 m2/s.