Electro-Magnetic Acoustic Transducer (EMAT)
It is the sure technique when ultrasounds nor piezoelectric transducers can not be used, for different reasons: be it a very high temperature, couplant presence, or the material type.
An EMAT transducer is composed of a magnet and an electrical coil, and depends on the electromagnetic interaction in order to generate elastic waves. With the Lorentz Force and magnetostriction, the EMAT transducer and the metal testing surface interact and generate a sound wave into the material. The material to be inspected is, in fact, its own transducer. Since it is not possible to use coupling between the transducer and material, EMAT technology is particularly indicated for automatized inspections in difficult environments.