Non-destructive testing (NDT) is a new subject that studies the physical and geometric properties of the tested materials and workpieces, monitors the macro cracks, inclusions and other defects, evaluates the changes of chemical composition, internal structure and mechanical properties, and then evaluates their adaptability without damaging the tested materials and workpieces. It has been widely recognized by industries. Eddy current testing technology provides a low-cost rapid large-scale inspection method with the advantage of zero-contact, so eddy current NDT method has become very important and widely used for testing/evaluation of the surface or near surface quality of conductive materials.
Pulsed eddy current testing is a new eddy current non-destructive testing technology developing rapidly in recent years. Wide frequency spectrum and the ability to detect different-depth flaws on the surface or near surface of the specimen with only one single scan, make it a research hotspot in the field of non-destructive testing.
Pulsed eddy current testing uses a repetitive broadband pulse excitating coil to induce instant eddy current on the tested sample through the instantaneous current generated in the coil. Under the effect of the excitation current, a rapidly attenuating pulsed magnetic field will be generated in the coil. The instantaneous eddy current and the rapidly decaying magnetic pulse will propagate in the material together to form a decaying induction field. The testing coil will output a series of voltage and time signals. Because the generated pulse is composed of a wide band spectrum, the responsing signal contains important depth information, which provides an important basis for the quantitative evaluation of materials.