For short ranges, as bulk waves or as lamb waves, EMATs offer adequate sensitivity with the important benefit of not requiring ultrasound liquid couplant or direct contact with the test surface. Test surfaces can also be quite rough without loss of sensitivity, as long as the EMAT coils are close enough to the surface to induce eddy currents. This normally requires a gap of less than 0.5mm. Another advantage of EMATs over PZT transducers arises where curvature reduces the amount of contact between a flat PZT element and the surface when testing pipes. The EMAT efficiency does not rely on this, since the performance can tolerate a degree of so-called lift-off between coils and surface.
The primary aim of including an EMAT to complement the measurements performed with the LRUT collar is to provide a method of evaluating with precision the indication detected by the LRUT. This means moving the EMAT sensors to the position of the indicator in order to scan with the EMAT.
Prototype PPM type EMATs were investigated in the original SubCTest project, commercial solutions for that are already available and will be used to develop the new scanning proposed in this project.