Short-Pulse Terahertz System for Layer Thickness Measurement
When measuring layer thickness in industrial environments, there are often sources of interference that cause vibrations and oscillations and thus falsify the measurement results. These interference signals are generated in the production environment, for example, by presses, punches, moving forklifts and trucks. In addition, during time-of-flight measurements, the robot arm vibrates slightly when it stops, which is also problematic. The Fraunhofer ITWM has developed a solution which, despite these sources of interference, enables non-contact and non-destructive reliable measurements: the short-pulse terahertz system.
In analogy to ultrasonic measurements, short terahertz light pulses are sent to the sample, with the difference that no coupling medium such as gel or water is required for terahertz measurements. Light pulses are reflected at each interface – the transitions between different layers such as paint and metal. These echo signals, arriving one after the other, provide information about the sequence and spacing of the layers. The measurements are then evaluated by comparison with a simulated measurement signal. The system has proven its worth in the final inspection of car coatings.