Terahertz imaging: a new non-destructive technique for the quality control of plastic weld joints

S. Wietzke; C. JÃ¶rdens; N. Krumbholz; B. Baudrit; M. Bastian; M. Koch

doi:10.2971/jeos.2007.07013

Journal of the European Optical Society - Rapid publications, Vol 2 (2007)

Terahertz imaging: a new non-destructive technique for the quality control of plastic weld joints

S. Wietzke, C. JÃ¶rdens, N. Krumbholz, B. Baudrit, M. Bastian, M. Koch

Abstract

We present the first investigation of plastic weld joints using terahertz waves. Terahertz time-domain spectroscopy clearly reveals contaminations like metal or sand within the weld joint of two high-density polyethylene sheets. Furthermore, areas can be identified where the welding process has failed and the parts to be joined are separated by a small air gap. We show that a three layer structure of polyethylene-air-polyethylene has a characteristic, frequency-dependent transmission behaviour. This allows for a distinction between welded and non-welded material as well as for the calculation of the air layer thickness from the relative transmission spectrum. Consequently, terahertz time-domain spectroscopy provides a promising new non-destructive and even contactless technique, which is desired by the plastics industry for detecting a variety of deviations from the ideal welding process.

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