Active thermography is based on the evaluation of a previously excited heat flow in the tested component and its disturbance by hidden defects.

The heat flow is generated with a heat pulse or through sinusoidal modulation. Testing is carried out with an IR-camera, followed by a mathematical analysis of the measured sequence to extract the information necessary for reliable defect detection. The applications of thermographic methods to measure defects (or porosity) quantitatively and to assess parts with a complex 3D-structure still hold unsolved problems. Induction thermography is a special kind of active thermography for the characterisation of metals.

 

In induction thermography the excitation is done by means of a HF-field and eddy currents are subsequently induced19. Since eddy currents are influenced by the presence of cracks, the latter can in principle be detected thermographically.