Tailoring Electromagnetic Loss Pathways in Hybrid Graphene-COOH/Fe3O4 Coatings via Thickness-Ratio Engineering and Multilayer Ordering

Achieving broadband microwave absorption (RL < −10 dB) across the combined X and Ku bands (8–18 GHz) with minimal coating thickness remains a significant challenge for electromagnetic interference (EMI) shielding. This study systematically investigates the design of hybrid Graphene-COOH/Fe 3 O 4 absorbers by treating layer ordering and thickness partitioning as primary optimization variables. Using full-wave simulations driven by frequencydispersive material parameters derived from experimental measurements, we demonstrate that stacking order is non-interchangeable; placing Fe 3 O 4 at the incident interface minimizes surface reflection, allowing effective wave entry. An optimized bilayer configuration (ttot = 4.0 mm) achieves significant bandwidth but remains limited by a single impedance transition. To overcome this, we propose a quadlayer architecture (ttot = 4.1 mm) that utilizes a staged impedance-and-loss budget to distribute dissipation across multiple interfaces. Depth-resolved power-loss density analysis reveals that this staged architecture serializes magnetic and dielectric loss mechanisms, significantly enhancing angular robustness and extending the continuous absorption bandwidth compared to the bilayer baseline. These findings establish architecture-driven design rules for realizing thin, high-performance absorbers in the 8–18 GHz frequency window. • Broadband microwave absorption targeted across 8–18 GHz at minimal thickness. • Layer ordering strongly influences impedance entry and loss-pathway continuity. • Optimised bilayer achieves RL ≤ −10 dB with 4.0 mm total thickness. • Quadlayer architecture distributes impedance–loss budget to extend bandwidth.