EMAT and Applications

EMAT or Electro Magnetic Acoustic Transducer is an Ultrasonic Testing (UT) technique. An EMAT induces ultrasonic waves into a test object with two interacting magnetic fields. A relatively high frequency (RF) field generated by electrical coils interacts with a low frequency or static field generated by magnets to generate a Lorentz force in a manner similar to an electric motor. Because of the Lorentz force molecules start vibrating and which in turn creates ultrasonic waves. This ultrasonic waves travels through the material and in a reciprocal process, the interaction of elastic waves in the presence of a magnetic field induces currents in the receiving EMAT coil circuit.

Applications

In-service inspection is possible.
No couplant is needed, Dry inspection.
Non-contact method. Proximity is preferred.
High speed of inspection.
Curvature of the work surface has less effect on the results.
High temperature and low temperature inspection.
Less sensitive to surface condition. It can inspect through coatings and are not affected by pollutants, oxidation, or roughness.
Easier for sensor deployment. Snell’s law of refraction does not apply, and the angle of the sensor does not affect the direction of propagation.
Easier to generate SH-type waves.

Advantages

High Temperature Thickness Gauging.
Boiler Water/Furnace Wall Tube Inspection.
Corrosion and erosion measurement.
Pipeline in-service inspection.
Flaw detection, such as, inclusions, de-laminations and disbond.
Acoustic velocity measurement.
Anisotropy and stress measurement.
Material characterization.
Easier to generate SH-type waves.