Anisotropic Microwave Properties of Some Aminated Carbon Fibers in the X-Band

In this work, we investigated the microwave properties of ethylenediamine (En)- and sulfonylethylenediamine (SuEn)-aminated carbon fibers (CFs) derived from polyacrylonitrile (PAN CFs) within the X-band frequency range (8–12 GHz). Microwave measurements revealed that both En- and SuEn-aminated PAN CFs exhibited higher attenuation constants than the unmodified PAN CFs, indicating greater internal energy dissipation of electromagnetic waves. Furthermore, the results demonstrated that attenuation is anisotropic, depending on the alignment of the CF axis relative to the polarization of the electric field of the incident electromagnetic wave. This anisotropic attenuation, combined with the presumably anisotropic characteristic impedance of the modified CFs, led to significantly direction-dependent transmission and reflection coefficients. Compared to the SuEn-aminated PAN CFs, the En-aminated PAN CFs showed the most promising performance, exhibiting both enhanced microwave losses and reduced reflection relative to the unmodified PAN CFs. The combination of these properties makes En-aminated PAN CFs particularly suitable for electromagnetic shielding applications, where effective wave absorption and minimal reflection are critical. These findings underscore the potential of chemically functionalized PAN CFs as advanced materials for electromagnetic interference shielding in applications ranging from military stealth technology to commercial electronic protection systems.