Meta material unit-cell design and orientation effects in conductive fused filament formed polymer for EMI shielding effectiveness

Electromagnetic shielding performance in additively manufactured conductive polymers is strongly dependent on geometry; however, the influence of unit-cell orientation in meta-structures remains insufficiently quantified in microwave conditions. In this work, a polyhedral metamaterial unit cell is designed in conductive PLA–carbon black and fabricated as WR-90-compatible shielding inserts by periodic tiling in four orientations, namely Variants 1–4. Shielding effectiveness is measured experimentally over 8.2–12.4 GHz and benchmarked against full-wave electromagnetic simulations. Despite identical outer dimensions, the four variants exhibit distinctly different responses, ranging from ~ 20 to 70 dB. Notably, Variants 1 and 2 have nearly identical mass (< 2% difference) yet differ by ~ 25 dB across the band, demonstrating an orientation-dominated effect beyond material quantity. This behaviour indicates that orientation governs attenuation primarily through increased effective propagation path length and geometry-induced impedance modulation. Variant 2 provides the highest broadband shielding (~ 50–70 dB), whereas Variant 3 yields the lowest (~ 16–31 dB). Discrepancies between simulation and measurement are mainly due to uncertainties in the bulk material approximation and print-induced geometric deviations.