Shearography and active thermography have received considerable industrial acceptance for nondestructive testing &
evaluation (NDT&E). They are applicable to all materials: metal, non-metal, composites materials and even biological
tissues. The principles and the methods of testing of these two techniques are reviewed, and their advantages and
limitations are being compared. Both are optical techniques enjoying the advantages of full-field, non-contact and hence
very high inspection speed. A fundamental difference between them is the mechanism of detecting flaws. Shearography
is an interference optical technique which measures surface deformation and reveals flaws by looking for flaw-induced
deformation anomalies. Active thermography is a surface thermal radiation measuring technique; it used thermal
radiation properties to measure the distribution of surface temperature of the object. It detects flaws by the flaw's
anomalous heat transfer response. The methods of testing are also different. While shearography requires application of
stresses to produce deformation, active thermography needs a controllable thermal radiation excitation to change the
surface temperature. Both shearography and active thermography can detect surface and sub-surface flaws, unless the
flaw is too remote from the surface.
Different excitation methods, such as sonic, induction, flash heating, for the techniques are demonstrated together with
some NDT&E applications such as detection of cracks, debonds and other type of flaws.