Beyond reflection loss: True absorption-dominant EMI shielding mechanisms in MWCNT–magnetite thermoplastic composites

Electromagnetic (EM) pollution arising from modern wireless systems has intensified the demand for lightweight, durable, and high-performance absorption-dominant shielding materials. Most reported electromagnetic shielding materials are based on thermosets and exhibit limited impedance matching, thereby restricting their applicability in next-generation wearable technologies. In this study, thermoplastic polyethersulfone (PES) nanocomposites were fabricated using four filler architectures—MWCNTs, Fe₃O₄ nanoparticles, Fe₃O₄–MWCNT hybrids, and Fe₃O₄@MWCNT structures—to systematically compare their electromagnetic behavior and elucidate the underlying dielectric–magnetic mechanisms governing microwave attenuation. Because the samples were measured as unbacked and free-standing films, absorption was determined directly from A = 1 − R − T, rather than the classical RL(dB) expressions that assume metal-backed configurations. The complex permittivity and permeability were retrieved using the Nicolson–Ross–Weir method in the 8.2–18 GHz range. MWCNTs primarily enhanced the energy storage (ε′) and dielectric loss (ε″) through conduction and interfacial polarization, whereas Fe₃O₄ primarily reduced dielectric mismatch and enabled enhanced electromagnetic wave penetration by introducing magnetic loss contributions. The combined Fe₃O₄+MWCNT system (NC3) exhibited the most balanced dielectric–magnetic response. The optimum composition (50 wt% Fe₃O₄+ 5 wt% MWCNT) achieved ∼17–19% incident electromagnetic wave absorption in the X band and ∼19–22% in the Ku band, outperforming the MWCNT-only (NC1) and Fe₃O₄-only (NC2) nanocomposites. Overall, this study provides an absorption-dominant EMI shielding mechanism-oriented comparison of magnetic, dielectric, and hybrid fillers in a thermoplastic matrix, demonstrating the potential of PES-based nanocomposites for next-generation EMI shielding materials with high absorptivity applications.