Flexible Polyimide Foams Coated with Graphene Nanoplatelets/Fe₃O₄ for Absorption-Dominated Electromagnetic Interference Shielding, Broad-Band Microwave Absorption, and Sensor Applications

With the rapid development of 5G communication technologies, the high-performance electromagnetic interference (EMI) shielding materials with less secondary reflection for electronic devices have become an urgent demand in recent years. In this study, flexible open-cell polyimide (PI) foams containing graphene nanoplatelets (GN)/Fe 3 O 4 coatings for absorption-dominated EMI shielding were fabricated. The result shows that the EMI shielding efficient (EMI SE) of composite foam PI/GN/Fe 3 O 4 (PF/GN/Fe 3 O 4 ) can achieve 60.6 dB with a thickness of 6.0 mm along with an absorption coefficient ( A ) of 0.4–0.6, indicating excellent EMI shielding and a low reflection property. Furthermore, the optimal reflection loss ( R L ) of PF/GN/Fe 3 O 4 with a low GN loading can be up to −35 dB at 5.0 mm and less than or equal to −10 dB in the whole X-band with a thickness of ≥4.5 mm. In addition, the prepared composite foam PI/GN (PF/GN) exhibits good electrical conductivity of 2.5 × 10 3 S/m and sensing stability. Notably, this research systematically studied the application performance of the composite foam in EMI shielding, electromagnetic wave (EW) absorption, and sensing monitoring. The prepared composite foam can be applied as “Green” EMI shielding materials for flexible electronic devices due to the remarkable EW absorption properties.