KAISERSLAUTERN, Germany—A new study indicates that Terahertz (THz) technology could be used to give incredibly accurate readings of paint film thickness. THz radiation, electromagnetic waves on a band somewhere between microwave and infrared radiation, can penetrate certain solid, opaque materials.
A team from the University of Kaiserslautern and Fraunhofer Institute for Physical Measurement Techniques, also in Kaiserslautern, has published a paper describing how pulses of THz radiation can be used to measure specific layers of coatings. The paper, “Highly Accurate Thickness Measurement of Multi-Layered Automotive Paints Using Terahertz Technology,” was authored by Soufiene Krimi, Jens Klier, Joachim Jonuscheit, George von Freymann, Ralph Urbansky, and René Beigang.
The authors note that this technology could be especially useful in applications like automotive coatings with complex, multilayer coating systems. At this time, automotive coatings are generally measured using sensors that utilize magnetism, eddy currents, or ultrasonic technology.
When THz pulses are applied to a surface, an echo comes back from the substrate as well as from each individual coating layer. Individual layers can be measured according to the time delay observed between the different pulse echoes.
The paper isn’t the first to look into the use of THz radiation to measure film thickness, but the new study’s contribution is to refine the algorithm by which the measurement is calculated, making the method much more accurate than in the past. The study states that film thickness can be measured down to less than 10 microns. In some cases, layers as thin as four microns can be measured. The method’s accuracy is usually less than 1 micron, and the method works on metal, carbon-fiber-reinforced polymers and dielectric substrates.