Excitation of horizontally polarized shear elastic waves by electromagnetic transducers with periodic permanent magnets

Abstract

Theoretical and experimental results obtained with a new type of noncontact electromagnetic transducer are presented. The transducer differs from previous configurations in that a periodic permanent magnet and an axially wound coil are combined to produce a transversely directed periodic surface stress. It is demonstrated that this configuration can be used to generate horizontally polarized shear waves traveling along, or at a predetermined angle to, the surface of a thick metal object, horizontally polarized shear modes of a thin plate, or torsional waves in a tube. A model is presented for the radiation resistance of the transducer in semi-infinite samples and plates and supporting experiments are reported. Some advantages of this transducer in ultrasonic nondestructive evaluation of structural materials are summarized.