1, UES Inc, Beavercreek, Ohio, United States
3, Texas A&M University, College Station, Texas, United States
4, University of Dayton Research Institute, Dayton, Ohio, United States
Additive approaches for radio frequency (RF) applications such as direct-writing antennas and transmission lines are of interest for producing conformal, deployable, and low cost solutions. However, the variability in print geometry and the heterogeneity in ink conductivity present a challenge to reliable RF device fabrication. To address these issues, we performed a statistical analysis of the variation of a print geometry as a function of print path parameters and characterized the RF properties of the Ag ink as a function of frequency, post-processing, and under finite deformation. To characterize the geometric variability of the print, we used an X band (~8-12 GHz) frequency selective surface (FSS) based on 4 mm diameter Archimedean spirals. The FSS design required over a thousand spirals per specimen, which we individually imaged and analyzed for arm length, thickness and vertex variability. We utilized a conductive ink consisting of a polyurethane matrix loaded with 3-5 um diameter Ag flakes, creating a strain-dependent percolating network. While the ink may be composed of high conductivity particles, the surface roughness and internal rearrangement of the conductive percolating networks can strongly affect the ink’s RF behavior. Free space RF measurements of the FSS demonstrated that geometric and conductivity variations could not only reduce filtering performance, but also shift and broaden the filtered frequency regime. Collectively, these results highlight the importance of tailoring print parameters and ink processing for RF applications where performance becomes more sensitive to the limitations of additive manufacturing.