A low-loss and medium dielectric permittivity SrTiO₃/HIPS composite for rapid prototyping of next-generation microwave devices

Composite polymer/ceramic filaments for material extrusion-based fused filament fabrication (FFF) additive manufacturing, using strontium titanium oxide (SrTiO₃) ceramic fillers and high impact polystyrene (HIPS) thermoplastics were produced and their dielectric and physical properties characterised for the first time. Relative permittivity (ε_r), quality factor (Q × f) and dielectric loss (tanδ) were measured as a function of ceramic solids loading (vol%) at 5 GHz. ε_r = 4.6, Q × f = 38,378 GHz and dielectric loss tanδ = 0.001 were obtained for a SrTiO₃/HIPS ceramic polymer composite, with 15 vol% (46 wt%) solids loading. A Plackett–Burman design of experiments was used to optimize the printing process of the ST/HIPS composites. The results of this optimisation helped achieve 3D printed parts with near-full density (99 %) and ε_r = 5.3, tanδ = 0.001. The composite materials exhibit reduced dielectric losses compared with commercially available feedstocks for FFF that are currently used for functional prototyping in the radiofrequency and telecommunications industry.