Developing microwave absorbing composites with lightweight and wide absorption bands is an essential direction for electromagnetic wave stealth and shielding application. In this article, PAN/PMMA blend fibers and sheath-core blend fibers with PAN/PMMA as the sheath and PMMA as the core were spun by uniaxial and coaxial electrostatic spinning, respectively. Porous carbon nanofiber (PCNF) and hollow porous carbon nanofiber (HPCNF) were obtained after pre-oxidation and carbonization of the corresponding two precursor fibers. The microwave absorption composite samples with PCNF and HPCNF as absorbents and paraffin as matrix were prepared, respectively. Their electromagnetic parameters were investigated by the reflective-transmission network parameter method. The microwave absorption properties of the corresponding composites were calculated based on a model for a single-layer planewave absorber from electromagnetic parameters. The results showed diversity between the microwave absorbing performance of the composites filled with PCNF and HPCNF. HPCNF performs better than PCNF as an absorbent; that is, the lowest reflection loss of composite filled with HPCNF is -20.26 dB and the effective bandwidth (lower than -10 dB) is to 4.56 GHz, while the lowest reflection loss of a composite filled with PCNF is -13.70 dB, and the effective bandwidth (lower than -10 dB) is 2.68 GHz when the absorbent content is 7%, and the thickness is 3 mm. Much lower reflection loss and a wider absorption band could be expected from HPCNF. The presence of a hollow structure in HPCNF, which may increase the degree of polarization and provide more interfaces for the interference phase extinction of reflected electromagnetic waves, might help to improve the attenuation of electromagnetic waves and broaden the absorption band.
Keywords: composite; hollow porous carbon nanofiber (HPCNF); microwave absorption; reflection loss.