Thermal imaging becomes more and more important not only for contactless temperature distribution measurements (“passive” thermography) but also for active thermography (AT).

With AT the object of interest is stimulated by a defined external “event” which can be applied solitary or periodically. The thermal feedback of the object then is analyzed in relation to the external stimulus.

One of the methods is the thermal Lock-In technique which is a non-destructive-testing method (NDT) where a periodically stimulus is used.

With this presentation some examples for the thermal Lock-In technique will be presented for electronic and mechanical applications.

It will be shown that with this technique high spatial as well as high thermal resolutions of about 1mK can be reached which is below the current resolution of thermal imagers of about 15mK.