Determine the refractive index of plastics as a function of temperature

SKZ researchers develop new measurement method using terahertz technology

Temperature-dependent refractive index of a plastic. (Graphic: Marcel Mayr, SKZ)

In plastics processing, plastics are first melted and then formed into the desired shape. As part of the quality control process, characteristics such as the wall thickness of pipes are measured in a non-contact, non-destructive manner using various measurement techniques such as radar or terahertz (THz) technology. The refractive index is a material-dependent parameter that describes the factor by which electromagnetic waves travel more slowly through a material.

Early detection of production defects

Since the refractive index is temperature dependent, measurement positions in the production line are selected where the product has cooled down sufficiently. This means that there is no temperature-dependent error when measuring wall thickness using refractive index. Researchers at the SKZ Plastics Center have developed a measurement method based on THz technology that makes it possible to determine the refractive index of plastics as a function of temperature. "This now makes it possible to determine geometries such as wall thickness at an earlier stage, which leads to earlier detection of production errors and thus directly saves resources and reduces rejects," explains Marcel Mayr, Senior Scientist at SKZ. This adds another application to the possible uses of THz technology.