What is EMAT

What is EMAT?

What is EMAT? EMAT or Electro Magnetic Acoustic Transducer is an Ultrasonic Testing (UT) technique that generates the sound in the part inspected instead of the transducer.

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.

For ferromagnetic conductors, magnetostriction produces additional stresses that enhance the signals to much higher levels than could be obtained by the Lorentz force alone. Various types of waves can be generated using different combinations of RF coils and magnets.

Because the sound is generated in the part inspected instead of the transducer, EMATs have the following advantages over more conventional piezoelectric transducers:

  • Dry inspection. EMAT does not require couplant for transmitting sound, which makes it very well suited for inspection of very hot and very cold parts, and integration in automated environments.
  • Impervious to surface conditions. EMAT can inspect through coatings and are not affected by pollutants, oxidation, or roughness.
  • Easier sensor deployment. Not having wedges or couplant, Snell’s law of refraction does not apply, and the angle of the sensor does not affect the direction of propagation. This makes EMAT transducers easier to control and deploy.
  • Ability to generate SH modes. EMAT is the only practical means for generating shear waves with horizontal polarization (SH waves) without high mechanical pressure or low-density couplants that impede scanning of the part.

Wave Mode:

EMAT is capable of generating all wave modes used in ultrasonic testing, including some modes that are very difficult or impractical with conventional piezoelectric transducers. The table below provides a summary guide of the type of wave and technique available for different applications.

Wave Mode

Industry Standards & Quality Codes

As an ultrasonic technique EMAT can be used to meet ISO, AWS, API, MIL-STD and other international standards. Innerspec Technologies has already deployed systems designed to meet the following:.

  • API 5CT (ISO11960) and API 5L8 for tube and casing (OCTG).
  • EN10160 for plate.
  • MIL-STD 2154 for ultrasonic inspection of wrought metals.
  • CGA C-20 for high-pressure cylinder.