Construction of Hollow Carbon Nanofibers with Graphene Nanorods as Nano-Antennas for Lower-Frequency Microwave Absorption

Abstract

Electromagnetic (EM) wave absorbers at a lower-frequency region (2−8 GHz) require higher attenuation ability to achieve efficient absorption. However, the impedance match condition and attenuation ability are usually inversely related. Herein, one-dimensional hollow carbon nanofibers with graphene nanorods are prepared based on coaxial electrospinning technology. The morphology of graphene nanorods can be controlled by the annealing process. As the annealing time increased from 2 to 8 h, graphene nanospheres grew into graphene nanorods, which were catalyzed by Co catalysts derived from ZIF-67 nanoparticles. These nanorods can play the role of nano-antennas, which can guide EM waves into materials to enhance impedance match conditions. As a result, the carbon nanofibers with graphene nanorods possess a larger impedance match area with higher attenuation ability. The minimum reflection loss reaches −57.1 dB at a thickness of 4.6 mm, and the effective absorption bandwidth can cover almost both the S and C bands (2.4−8 GHz). This work contributes a meaningful perspective into the modulation of microwave absorption performance in the lower-frequency range.

Carbon vacancies regulation strategy for boosting the high-temperature microwave absorption performance of (Co0.2Mo0.2V0.2Nb0.2Ta0.2)Cx high-entropy carbides

“…S6, ESI†). 54,55 It can be seen that both the conductivity loss and polarization loss capacities tend to increase with increasing temperature. Therefore, it leads to the increase of ε ′′ with the increase in temperature.…”

Three-dimensional biotemplate-loaded nickel sulfide vacancies engineered to promote the absorption of electromagnetic waves

“…The ε ′ of Ni x S y @De and Ni x S y @De-etched show a decreasing trend with increasing frequency, which can be attributed to the characteristic dispersion response due to the enhanced hysteresis of the dipole polarization response to the electric field, which also improves the impedance matching of the incident microwave. 50,51 The ε ′ and ε ′′ values of the last two samples undergo a huge enhancement with respect to Ni(OH) 2 @De, suggesting that sulfide increases the dielectric properties of the samples in the form of phase components, vacancies, and defects. 52 The presence of abundant defects and a large number of interfaces after sulfurization was demonstrated by XRD, EPR, and SEM, leading to significant polarization, 53 thus synergistically contributing to the dielectric attenuation performance.…”

GO-decorated chain-like Fe2O3/FeMn2O4 NPs (GO-Fe2O3/FeMn2O4 nanocomposites) with ultrabroad band microwave absorption

“…The real parts of permittivity ( ε ′) and permeability ( μ ′) measure the ability to store electric and magnetic energy, which show the degree of polarizability of absorbent materials. 29–31…”