Study on the lift-off effect of EMAT

Non-contact inspection is the main advantage of the electromagnetic acoustic transducer (EMAT). However, it lowers the transduction efficiency between ultrasonic energy and electromagnetic energy. The lift-off of the transducer has a close relationship with transmitting and receiving ultrasonic signals, because it reduces the magnitude of the alternating magnetic field in the specimen. The distribution and intensity of the alternating magnetic field at different lift-off values are simulated in ANSOFT. The relationship between the lift-off and received signals is analyzed through experiments. Results show that the suitable lift-off value for this specific EMAT system should be around 2 mm, considering both sensitivity and stability of the transducer.