Double-layer electromagnetic shielding materials with microcellular structure for strong absorption and low reflection

Given the rapid development in information and communication technologies, there is a pressing need for efficient, broadband, and lightweight shielding materials that emphasize electromagnetic (EM) wave absorption. Traditional single-layer material faces challenges such as limited absorption and secondary reflective pollution. To address the issues, we constructed a double-layer composite structure composed of a microcellular absorption layer comprised of multi-walled carbon nanotube (MWCNT)/flake iron powder (Fe)/poly (vinylidene fluoride) (PVDF) and a highly conductive solid MWCNT/PVDF (20/80 vol.%) layer. By controlling the composition of MWCNT/Fe in PVDF and the void fraction (VF) using supercritical carbon dioxide foaming, the impedance matching and the EM attenuation capability of the absorption layer were effectively adjusted. A reflection loss (RL) as low as −60 dB and an effective absorption bandwidth of 3.44 GHz were obtained for MWCNT/Fe/PVDF (5/10/85 vol.%) with a VF of 75 %. By combining the absorption and shielding layers, an average total shielding effectiveness of 41.75 dB and reflectivity of 0.12 across the X-band were achieved with a thickness of only 3 mm. The employment of metallic magnetic micro-particles improves impedance matching due to their high saturation magnetization and ease of integration with the dielectric material MWCNT. The combination of the microcellular structure and the highly conductive layer allowed for the decoupling of impedance matching, attenuation, and shielding, resulting in an “absorption-reflection-reabsorption” pathway for dissipating EM energy. The heterogeneously structured double-layer composite with excellent shielding efficiency and low reflection characteristics presents a promising strategy for developing next-generation high-performance, absorption-dominant EM interference shielding materials.