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Pavel Pashkov

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EMAT (Electro-Magnetic Acoustic Transducer)

EMAT (Electro-Magnetic Acoustic Transducer)












General Information

EMAT is the abbreviation for Electromagnetic Acoustic Transducer. An EMAT is a non-destructive ultrasonic testing device, which has overcome many of the issues faced by the more conventional piezo probes.

An EMAT transducer consists of a case with a socket, an induction coil, a protective cover, a magnetic flux concentrator and a permanent magnet. Alternate current feeds the induction coil, causing electromagnetic oscillations, which, in turn, induce eddy currents on the surface of the test object. Eddy current interferes with the permanent magnetic field, creating ultrasonic waves directly on the surface of the test object. These waves propagate in the test object, reflecting and deflecting from the walls back to the EMAT coil. The picture created by the ultrasonic activity shows up flaws and defects within the test object.

One of the key advantages of the EMAT is that the ultrasonic waves are generated into material and received from it without direct contact between the UT-probe and the material, without a couplant.

As the ultrasound source is the surface of the test object itself, tilting the probe or changing the gap between the coil and plate do not affect the acoustic field or the direction in which the ultrasonic waves are generated. This is a huge advantage of an EMAT over a conventional piezo-probe. 

An EMAT is the only device that is able to transmit and receive transversal (shear) waves in this way. Waves transmitted by an EMAT allow much higher resolution and sensitivity to flaws than the longitudinal waves produced by piezo probes. 

This all makes EMAT an extremely effective instrument for non-contact ultrasonic examination of plates, strips, pipes, bars, billets and etc.


Main Advantages of the EMAT-based Ultrasonic Testing Systems:

- Ease of operation: EMATs are robust, non-contact ultrasonic probes, which do not need

  adjusting or calibrating;

- Ease of maintenance: the probes do not need servicing, nor do they change their

  physical properties during the testing procedure;

- Low operation costs: the probes do not require a couplant in order to transmit and

  receive ultrasonic waves;

- EMAT is relatively insensitive to the surface conditions of the material. As waves

  are generated directly on the surface of the test object; the angle of wave generation

  does not depend on the  inclination of the probe;

- Less personnel training required for EMAT testing as compared to

  conventional technologies;

- Heat resistant: Tests can be conducted at a temperature range of -40ºС to +650ºС;

- Background noise elimination: immunity that is unattainable for piezo-probes;

- Environmentally-friendly: As water is not need in the testing procedure, several thousand

  litres of high quality   water can be saved a year;

- High productivity: Tests can be run with up to 10 m/s speed;

- Kind to electronics: No water evaporation means that sensitive electronics are protected;

- EMAT is able to transmit and receive all type of waves applicable for

  conventional piezo-probes.






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