Eddy current non destructive testing

The operating principle of eddy current non destructive testing is based on the induction phenomena in conductive materials : when a alternative magnetic field reaches a electrically conductive mass, eddy currents appear in the mass.

French scientist Jean Bernard Léon Foucault has demonstrated the influence of eddy currents in many experiments which can be visited at the Conservatoire National des Arts et Métiers in Paris, France.

In non destructive testing, eddy currents can be used for probing the material: when they meet a void, crack or other defects inside the material, they change their path and their magnitude. Their behaviour gives precious information about the state of the material. So, there is no need to open the material to inspect it, but only to “light” the material with a magnetic field and “catch” the information about the induced eddy currents.

However, we can not measure directly the eddy currents. We can only measure the magnetic field they create. The non destructive testing with eddy currents consists of:

1.      Excite the material to be tested by a alternative magnetic field

2.      Measure the secondary magnetic field caused by eddy currents

3.      Analyse the properties of the measured magnetic field in order to determine the state of the tested material.