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 in a manner similar to an electric motor.

This disturbance is transferred to the lattice of the material, producing an elastic wave. In a reciprocal process, the interaction of elastic waves in the presence of a magnetic field induces currents in the receiving EMAT coil circuit.

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. EMATs do not require couplant for transmitting sound, which makes them very well suited for inspection of hot parts, and integrated in automated environments.
  • Impervious to surface conditions. EMATs can inspect through coatings and are not affected by pollutants, oxidation or roughness.
  • Easier probe deployment. Not having wedges or couplant, Snell's law of refraction does not apply, and the angle of the probe does not affect the direction of propagation. This makes them easier to control and deploy, especially in automated environments.

Wave Modes

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.

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.

EMAT is also specifically referenced in the following ASTM guides:

  • ASTM E1774-96 Standard Guide for Electromagnetic Acoustic Transducers (EMATs).
  • ASTM E1816-96 Standard Practice for Ultrasonic Examinations Using Electromagnetic Acoustic Transducer (EMAT) Technology.
  • ASTM E1962-98 Standard Test Methods for Ultrasonic Surface Examinations Using Electromagnetic Acoustic Transducer (EMAT) Technology.

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