Electromagnetic interference shielding anisotropy enhanced by CFRP laminated structures

Abstract Continuous carbon fiber reinforced polymers (CFRP) composites, particularly prepreg stacked composites, have anisotropic properties, including anisotropy of electrical conductivity and dielectric characteristics. These features lead to electromagnetic interference (EMI) shielding anisotropy of the CFRP. The coaxial transmission line method was used to test the EMI shielding of CFRP to clarify the EMI shielding anisotropy of CFRP. Moreover, the optimization of EMI shielding performance of CFRP by changing the composites’ structure were also investigated systematically. The anisotropy of EMI shielding was confirmed for the first time by the coaxial transmission line method. The results showed that a quasi-radial sample had the highest shielding effectiveness (25.8 dB) at 15 GHz, and the carbon fibers in this sample aligned in the direction of the electric field of electromagnetic waves. The orientation of fibers relative to the direction of electric field clearly affected the EMI shielding performance of the CFRP composites. The four-ply CFRP (0°/90°/0°/90°) with three cross-layers had the excellent shielding value of 28.9 dB at 15 GHz, that was far superior to that of a unidirectional CFRP (0°/0°/0°/0°) composite (SE = 18.6 dB), and it even outperformed an eight-ply unidirectional CFRP composite (SE = 22.6 dB). Laminated structures governed SE, and the number of cross-layers in the composites improved their EMI shielding performance. The shielding mechanisms of cross-layer CFRPs were also discussed and clarified based on both experimental and theoretical analysis. We believe that these findings could provide a scientific basis and potential in designing high-performance EMI shielding materials.