Improved Sensitivity in Microwave Assessment of Moisture Absorption in Polymeric Filaments Used in Additive Manufacturing

Polymer-based additive manufacturing (AM) has gained widespread utility, where rapidly producing complex parts is of interest. However, there are still many challenges that limit broader industrial adoption, which are related to the real-time and in-line inspection of the process. In a previous investigation a near-field microwave nondestructive testing (NDT) technique was developed for detecting and evaluating moisture absorption in polymeric filaments used in AM. This method involved loading an open-ended rectangular waveguide (OERW) with an optimally designed dielectric slab to make an extended dielectric-loaded waveguide (EDLW) probe. The dielectric insertion served to confine the electric field distribution in a smaller region compared to the OERW probe. This investigation improves upon that method by reducing the opening dimension of the waveguide aperture into a small slit improving measurement sensitivity and spatial resolution. Numerical electromagnetic (EM) simulations within the Ka-band (26.5-40 GHz) frequency range were conducted using CST Studio Suite and validated by conducting several relevant experiments.