Ultra-broadband microwave absorption in cobalt particle composites through nanoflake morphology and filler-gradient multilayer design

This research investigates the optimization of microwave absorption in cobalt particles containing composites through controlled particle morphology and multilayer absorber design. Flake-shaped Co particles were synthesized via a hydrothermal method using cobalt chloride, CTAB, NaOH, and hydrazine. X-ray diffraction (XRD) analysis confirmed the presence of Co phases, while field-emission scanning electron microscopy (FESEM) revealed a flaky morphology with an average thickness of 80 nm and diameter of 10 μm. The electromagnetic properties of composites containing paraffin wax and varying weight percentages (50%, 60%, and 70%) of Co nanoflakes were measured from 1–18 GHz. Furthermore, a filler-gradient multilayer design, employing paraffin as an impedance-matching layer followed by layers of composites with varying Co concentrations, significantly improved absorption performance. This optimized multilayer structure achieved an exceptionally wide absorption bandwidth of 14.8 GHz (3.2-18 GHz) with a minimum absorption of -10 dB and a maximum absorption exceeding -150 dB at 4.1 GHz, demonstrating the synergistic effect of particle morphology control and multilayer design in achieving superior microwave absorption characteristics. These findings offer valuable insights for the design and fabrication of high-performance microwave absorbers for various applications. • Flake-shaped Co particles (80 nm thick, 10 μm diameter) made via hydrothermal method. • Co nanoflakes show better dielectric properties as filler concentration increases. • Multilayer gradient design absorbs 14.8 GHz bandwidth (3.2-18 GHz). • Optimized structure achieves > -150 dB absorption at 4.1 GHz. • Particle shape and multilayer design synergistically enhance wide absorption efficiency.