Simple synthesis of hollow CoFe carbon fiber composites with enhanced heterogeneous interfaces and impedance matching for broadband microwave absorption

One-dimensional (1D) carbon nanofibers with unique three-dimensional (3D) network structure and high electrical conductivity are an important microwave absorbing material. However, due to poor impedance matching and single loss mechanism, its effective absorption bandwidth (EAB) is limited. Therefore, in this work, a porous hollow carbon fiber is designed using coaxial electrostatic spinning, and the magnetic component CoFe alloy is introduced during high temperature sintering to prepare porous CoFe hollow carbon fiber composite (CF@HCF). Its unique 1D nanostructure and 3D interconnected structure facilitates multiple reflection losses of electromagnetic waves within the material. In addition, the presence of porous and hollow structures increases heterogeneous interfaces and surface area. The introduction of magnetic components on carbon fibers not only increases the magnetic loss, but also forms a variety of heterogeneous interfaces. In addition, the porous hollow structure improves the spatial efficiency and porosity of the composites, thus optimizing impedance matching. The results indicate that, at a filler ratio of 25 wt%, the EAB reaches 7.04 GHz, with a minimum reflection loss (RL min ) of −50.04 dB under a matching thickness of 2.4 mm. In addition, to extend practical applications, CF@HCF composite membrane with excellent flexibility was prepared using PDMS encapsulation technology, and the sample also shows an average electromagnetic shielding performance of >30 dB. Besides, the radar cross section (RCS) values are below −10 dB m², demonstrating the material's significant radar wave attenuation capability and practical application potential. This work provides some perspectives on the preparation of hollow carbon fiber magnetic powder composites, and lays the foundation for the application of magnetic carbon-based composites.