Electromagnetic Wave Absorption Characteristics of Patterned BaTiO₃/BaZnCoFe₁₆O₂₇ Bilayers with Controlled Layer Thickness and Pattern Geometry

This study explores the electromagnetic (EM) wave absorption behavior of a bilayer structure comprising BaZnCoFe₁₆O₂₇-epoxy (BZCFO) and BaTiO₃-epoxy (BT). BZCFO exhibits magnetic loss via ferromagnetic resonance (FMR) originating from BaZnCoFe₁₆O₂₇ particles, while BT provides high permittivity and dielectric loss due to the ferroelectric nature of BaTiO₃ particles. The composite samples were prepared by individually mixing the synthesized single-phase powders of BaZnCoFe₁₆O₂₇ and BaTiO₃ with 10 wt% epoxy. The complex permittivity and permeability of each layer were experimentally determined and applied in HFSS simulations across the 0.1–18 GHz frequency range. To ensure the accuracy of the simulation, the reflection loss (RL) results of the single-layer BZCFO structure were compared with experimental measurements and calculations based on transmission line theory. Based on this, various bilayer configurations were examined by adjusting the thicknesses of BZCFO (tBZCFO) and BT (tBT), and applying different BT layer patterns: non-patterned, cross-shaped, and square island types. The non-patterned bilayer exhibited lower performance than the optimized single BZCFO layer, with increased tBT causing reduced absorption due to stronger reflection. In contrast, the cross-shaped pattern exhibited enhanced broadband absorption when tBT = 0.2 mm, tBZCFO = 2.25 mm, and the pattern width was 1.0 mm, achieving an absorption bandwidth (Δf) of 12.51 GHz where RL remained below –10 dB. In the case of the square island pattern, an excellent absorption bandwidth of Δf > 12 GHz was achieved when the BT squares had a side length of 0.75 mm and covered approximately 2–14% of the BZCFO surface. These results highlight the potential of tailored dielectric–magnetic bilayers with patterned structures for broadband EM wave absorption and shielding applications.