Correlation of printing faults with the RF characteristics of coplanar waveguides (CPWs) printed on nonwoven textiles

Printing high-resolution microwave passive devices directly on textile surfaces presents many challenges due to the high surface roughness and porosity of textile materials. This paper explains in detail physical and electromagnetic characterization of screen-printed coplanar waveguides (CPWs) on nonwoven textiles with a surface roughness of approximately ∼18 μm. Three different screen mesh counts (mesh opening unit) are used to screen print CPWs with five different resolutions. A screen printable silver paste is used as a conductive ink during the screen printing process. The difference in screen mesh counts affects the line resolution, thickness, conformity, and overall power transferring capacity of printed CPWs. A print resolution of 220 μm as the gap between the parallel lines of CPWs is achieved in this work without any surface modification of textile media. The surface roughness of the printed silver track is very similar to the base fabric (18 μm) when the screen with 305 mesh-count is selected for printing. Additionally, the thickness of the ink on the fabric is most conformal and lowest (23.4 μm) for the similar selection of screen mesh count. Fabricated CPWs are characterized for signals from 0.5 GHz to 10 GHz and compared to electromagnetic 3D simulation results. This paper also identifies minute printing faults in the 3D structure of the printed CPWs and correlates that with the scattering parameters of the transmission lines. Simulated and experimental data prove that a well-designed and process optimized printed nonwoven-based CPW works well (i.e. below 3 dB of insertion loss) for frequencies ranging from 0.5 GHz to 7 GHz.