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Monitoring of air voids at plastic-metal interfaces by terahertz radiation

May 12, 2020

Pałka, Norbert, Andrzej Rybak, Tomasz Jakubowski, Marek Florkowski, Marcin Kowalski, Przemysław Zagrajek, Marek Życzkowski, Wiesław Ciurapiński, Leon Jodłowski, and Michał Walczakowski. “Monitoring of air voids at plastic-metal interfaces by terahertz radiation.” Infrared Physics & Technology 104 (2020): 103119.


The time domain spectroscopy (TDS) setup in a reflection configuration was exploited for non-destructive measurements of four samples with a 10-mm (approx.) leaf-shaped air void at the interface between the plastic and metal structures. We identified and measured the material parameters of the samples required for precise determination of the voids’ thicknesses in the range of 125–500 μm. For high resolution measurements we selected the reflection TDS setup with a short focal length and developed a method for the accurate calculation of the incidence angle. We used a deconvolution-based method for thickness monitoring of voids and discussed its limitations. The two-dimensional thickness, amplitude and binary maps were exploited for imaging of the void areas. We also showed that the multiplication of the deconvolved and binarised maps can provide relevant information about the real thickness of the layer and the presence of the void in the single image. The correlation coefficient between the real and TDS measured shapes of the leaf in the range 0.8–0.9 suggests a good perspective for this technique in industrial applications.