A novel methodology for designing Mono/Bi-slab X-band microwave absorbers of Carbon-Powder composites

Abstract

This work introduces a methodology for the design of X-band microwave absorbers using carbon-graphite powder composites. The reflection loss (RL) is adjusted through variations in sample thickness, mono/bi-slab geometries, and effective dielectric constant. The impact of the particle size of the powders and the volume fraction (v.f.) of the composites on the effective dielectric permittivity has been systematically investigated. The Nicolson-Ross-Weir (NRW) conversion and the Birchak dielectric mixing model were employed. Optimal absorption conditions predicted by RL simulations were validated through experimental waveguide measurements for mono/bi-slab systems of paraffin-carbon composite samples. The mono-slabs with a particle size of 3.5 μm showed the best versatility for tailoring the RL in the X-band through v.f. variations while maintaining a fixed thickness of 2 mm. In addition, a bi-slab system (powder-paraffin/paraffin) for such powder size, at 18.0 % of v.f., showed an enhanced RL with a bandwidth of 2.6 GHz and a minimum of − 40 dB (at 11 GHz). Other dielectrics based on resin:paint mixtures were tested to replace the paraffin-matrix, revealing a strong powder-matrix interaction capable of modulating the effective dielectric permittivity. Finally, experimental antenna RL measurements conducted in free space were corroborated by theoretical simulations based on the waveguide characterizations.