Influence of Al-dispersion and double layering on the microwave absorption behaviour of B ₄ C

Boron carbide (B 4 C) is recognized for its low density, and excellent thermal stability, making it a strong candidate for ceramic-based microwave-absorbing materials. The present study focuses on the influence of Al-dispersion on electromagnetic attenuation behaviour of B 4 C. The Al/B 4 C composites were synthesized via high-energy mechanical ball milling with Al dispersion from 2 to 10 wt.%. Phase constitution and magnetic response were examined using X-ray diffraction and vibrating sample magnetometry, confirming phase stability of B 4 C and the non-magnetic nature of the composites. Microstructural analysis using Field-emission scanning electron microscopy coupled with energy-dispersive spectroscopy mapping demonstrated homogeneous Al dispersion throughout the B 4 C matrix promoting the formation of abundant heterogeneous interfaces. Dielectric properties and reflection loss were evaluated using a vector network analyzer over the 2–18 GHz range. Among the single-layer absorbers, sample BA1 (2 wt.% Al) exhibited the minimum RL of −42.75 dB at a matching thickness of 1.1 mm, with an effective absorption bandwidth of 2.19 GHz (RL < −10 dB). Sample BA4 (8 wt.% Al) showed the maximum effective absorption bandwidth (RL < −10 dB) of 2.63 GHz, indicating that increasing Al content improves bandwidth via enhanced conductive loss and interfacial polarization. To further broaden absorption performance, a double-layer absorber was designed, and layer sequences and thicknesses were optimized using a genetic algorithm (GA). The optimal configuration, BA3 as the front layer and BA1 as the backing layer, each with a thickness of 1.0 mm, achieved a substantially enhanced bandwidth of 5.7 GHz while maintaining >99% absorption efficiency across the operating band. The novelty of this work lies in demonstrating that controlled Al dispersion in B 4 C, combined with GA-assisted double-layer design, enables thin and broadband microwave absorption without magnetic fillers.