Design and fabrication of functionally graded Ba_0.6Sr_0.4TiO₃/ Polyetheretherketone composites with tailored dielectric properties via fused deposition modeling

This study presents a novel approach for fabricating Ba_0.6Sr_0.4TiO₃/Polyetheretherketone (BST/PEEK) composites with spatially graded dielectric properties using fused deposition modeling (FDM). To achieve localized property control, composites were engineered with gradient cylindrical cavities of varying diameters (1–4 mm). Experimental characterization demonstrated that the dielectric permittivity and its tunability under DC bias exhibited an inverse relationship with cavity size; permittivity decreased from 7.62 (1 mm cavities) to 5.45 (4 mm cavities), while tunability dropped from 18.71 % to 6.79 %. The effective medium theories (EMTs), including the Yamada model, Bruggeman model, Differential effective medium, etc., were successfully applied to predict the composite permittivity, showing strong agreement with experimental data (error <5 %). By strategically arranging these cavity designs, composites with pre-programmed permittivity gradients were realized. The potential of this tailored substrate was demonstrated through a tunable multi-frequency antenna, which achieved a shift in central operating frequency (2.7–10 %) under DC bias across 5G, satellite, and industrial IoT bands (3.0, 3.3, and 3.7 GHz). This work effectively integrates theoretical modeling with additive manufacturing for developing functionally graded composites for advanced RF and bioelectronic applications.