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Study Advances Film Measurement

Thursday, July 14, 2016

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Terahertz technology is already in use or in development for applications including security and medical imagery, but a new study indicates it could be used to give incredibly accurate readings of paint film thickness.

Terahertz (THz) radiation—electromagnetic waves on a band somewhere between microwave and infrared radiation—has been studied for decades, but only in recent years have scientists begun to discover how to harness it. THz waves can penetrate certain solid, opaque materials, making the technology promising for uses like seeing through luggage.

Auto parts being painted
© / GregorBister

The authors note that the terahertz technology could be especially useful in applications like automotive coatings, with complex, multi-layer coating systems.

A team from the University of Kaiserslautem and Fraunhofer Institute for Physical Measurement Techniques, also in Kaiserslautem, has published a paper in the July 12 issue of Applied Physics Letters, describing how pulses of THz radiation can be used to measure specific layers of coatings.

The authors note that this technology could be especially useful in applications like automotive coatings, with complex, multi-layer coating systems. At this time, automotive coatings are generally measured using sensors that utilize magnetism, eddy currents or ultrasonic technology.

How It Works

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, the research team explains, 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—the idea has been brought up by several researchers over the past 10 years—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 holds 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 study notes that the method’s accuracy is usually less than 1 micron, and the method works on metal, carbon-fiber-reinforced polymers and dielectric substrates.

The Authors

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.

“Our approach presents a framework that takes into consideration real industrial challenges such as the effect of wet-on-wet spray in the painting process,” explained Beigang, the study's lead researcher. “This is important because the multi-layer car coating process is complex, and a new approach is needed to improve vehicle paint quality control."


Tagged categories: Asia Pacific; Coating/Film Thickness; Colleges and Universities; EMEA (Europe, Middle East and Africa); Latin America; North America; Quality Control; Research; Thickness gauge

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