Broadband microwave absorption with ultra low filler ratio through one step direct calcination of the pappi of Ceiba speciosa (A. St.-Hil.)

Abstract

The fast growing demand for constant updating of information technology has made its side effect of electronic interfere and radiation a prominently serious problem. Compared with other types of MA(microwave absorption) absorbers, biomass-based absorbers are a highly promising sort, due to their low weight, possession of unique intrinsic structures, and low cost, which is essential for practical use. However, owing to their exorbitant relative complex permittivity, the undesirable impedance mismatching has often been obtained, which typically leads to both limited MA capabilities and a narrow effective absorption band. Hence, various strategies such as activation processes or doping of magnetic materials have been employed to boost the MA performances of biomass based materials, and these further modifications will inevitably add cost, making the advantage of low cost for biomass at least compromised or even lost. This research employs the silky pappi of the fruit of Ceiba speciosa (A. St.-Hil.) to furnish biomass-derived absorbers through one-step direct calcination. Together with high aspect ratio, its unique tubular hollow structures can act as resonators, which allows for multiple reflections and scatterings, highly facilitating the dissipation of undesirable energies. The results show that the sample annealed at 700 ℃ (Cs-700) has effective absorption bandwidth as wide as 9.3 GHz (8.7–18 GHz) at the thickness of 3.36 mm under the ultra low filler sample ratio of only 7%. Moreover Cs-700 presents broadband absorption at all the five tested thicknesses with the narrowest band of 6.2 GHz. Furthermore, when calcination temperature was risen to 800 ℃, much inferior effective bandwidth, the maximum of which is only 5.8 GHz, has been found. Thus, high aspect ratio, unique hollow tubular structures, as well as a subtle balance of between attenuating abilities and impedance matching account for the exceptional MA performance of Cs-700. We believe these findings open a window for the future structure design of biomass based MA materials.