EMAT technology overview
The EMA transducer consists of a permanent magnet and an induction coil. A high-frequency current pulse flows through the induction coil leading to generation of eddy currents in the surface layer of the test object. Charged particles in the surface layer of the test object create a current opposite to the current in the induction coil, and Lorentz force, directed along the surface of the test object, acts on these particles in a constant magnetic field. As a result, mechanical displacements occur in the areas with eddy current and the acoustic wave is generated. Cracks, corrosion, and other defects disrupt the guided ultrasonic wave, causing a reflected echo signal. Based on the analysis of the reflected echo signal, we can judge about the state of the test object.Advantages of EMAT technology (as compared with the usual ultrasonic testing)
No need in contact fluid No need in surface grinding or polishing
No distortions of acoustic wave in the external environment (the wave is generated directly on the surface of the test object)
Wide range of frequencies and various types of waves (Lamb waves, Rayleigh waves, longitudinal waves, transverse waves with horizontal, vertical and radial polarization) enabling increase in the measured range and measurement accuracy and operation with complex geometric items
Not sensitive to inclination angle of the transducer relative to the surface of the test object
No need in sensor contact with the surface (a gap can be up to 10 mm)