Mechanism of Detecting Ultrasonic Waves by an Electromagnetic Acoustic Transducer.

This paper investigates the mechanism of an electromagnetic acoustic transducer(EMAT). EMATs can generate and detect ultrasonic waves in a conductive specimen by noncontact electromagnetic coupling. This feature gives EMATs an advantage over conventional ultrasonic transducers : theoretical modeling and formulation based on elastodynamics and electromagnetics can be obtained. The process of detection by EMATs, however, has not been well studied theoretically so far. Thus, in this research, the process of detection by an EMAT as well as that of transmission has been analyzed numerically. Predicted signals of a receiver EMAT agree well with experimental results, which validates our numerical approach. Computed elasto-acoustic fields show us how ultrasonic waves propagate in the specimen, reflecting with mode conversion on the surface. Moreover, the mechanism of detection has been explained by using numerical results of electromagnetic field induced by ultrasonic waves. These results can be useful to establish a method of inverse flaw identification by EMATs in the field of nondestructive testing.