TeraView Brings New Techniques to the Study of Industrial Coatings
TeraView,which is commercialising active terahertz technology, now brings techniques developed for medicine and pharmaceutical products to non-destructive testing for coatings, studies of adhesion.
“First, we have to distinguish between active and passive terahertz, ” explains Professor Sir Michael Pepper, Scientific Director for TeraView. “In the passive case the terahertz emitted by objects measured has no industrial relevance, unlike the active case, which measures the response to illumination by terahertz generated in our equipment.”
Terahertz radiation is situated between the microwave and infra-red and until recently was not utilised in any significant way. However the situation changed when TeraView (founded 2001 in Cambridge UK), showed that it was possible to image a human tooth with more detail than X-Rays. Using a successive sequence of pulses, the non-ionising technology, with its 3-dimensional reconstructions and depth resolution better than 10-3 cms, could also differentiate cancer from healthy tissue now in clinical trials.
“The basis for the action of terahertz is that it acts rather like high frequency radar,” Pepper adds. “The radiation is reflected each time there is a change in material. The time of arrival is measured and then various algorithms complete the picture by developing 3D fine feature images and precise material identifications.”
How does this pertain to industrial coatings?
Terahertz can measure thickness across a substrate precisely and it can also obtain the density of the coating. Unlike ultrasonics, the probe is not in contact with the sample and no preparation of the sample is required. It is totally non-invasive.
Delamination of coatings are also detectable using terahertz. If two surfaces have bonded effectively, there is a graded region where one passes into the other, either utilising adhesives or else by chemical bonding. The amplitude of the terahertz reflection and the line shape can be used to obtain the strength of the bond and assess whether delamination has occurred locally or whether it is likely to occur.
The technology has considerable relevance to composite coating materials, where layers are deposited sequentially. Terahertz can detect if a defect is present, including foreign inclusions, impurities, stresses on film formation.
Because the measurements of coating films are real time (a single pixel, taking about 20 milliseconds), measurements can be taken during the coating process to give an accurate picture of what is taking place in a deposition chamber or similar equipment.
These are just a few examples of the remarkable scope and power of terahertz imaging.