Nondestructive testing (NDT) and condition monitoring (CM) are vitally important in many branches of manufacturing because they make it possible to test products for quality and safety without causing damage. Many techniques have been developed for the purpose. Terahertz (THz) is a new addition to the toolbox of NDT and CM.
THz is an optical non-contact technique that can be implemented inline or offline. It employs non-ionizing far-infrared wavelengths between 100 and 1000 micron to sense material properties, detect faults and visualize structures. It is similar to X-ray in its operation, but unlike X-ray it is safe because it uses low-energy beams. The range of wavelengths is similar to ultrasound, but unlike ultrasound it is optical, non-contact and does not require immersion in a medium. THz can be employed to examine a wide variety of products. Most insulating materials are transparent or semi-transparent to THz and can be examined by THz beams in transmission or reflection, revealing their dielectric properties and internal structures.