Design and preparation of an ultrawideband gradient triple-layered planar microwave absorber using flaky carbonyl iron as absorbent

Ultrawideband microwave absorbers have wide applications in civil industries and stealth technology. To achieve an ultrawideband absorption, flaky carbonyl iron particles (FCIPs) fabricated by a ball milling method were used as absorbents. The electromagnetic parameters of six FCIPs/wax absorbing composites with different weight ratios were measured in the frequency ranges of 2–18 GHz and 26.5–40 GHz. With these composites, particle swarm optimization was applied to design an ultrawideband triple-layered planar microwave absorber according to the absorbing performance calculated by the transmission-line theory. The reflection loss (RL) of the designed 6 mm thick absorber is below − 10 dB in 91% of the concerned bands. According to this design, a gradient triple-layered sample was prepared. Its measured RL is below − 10 dB in more than 90% of the concerned bands, although there are some shifts of the absorption peaks comparing with the simulated result. Benefiting from both the λ/4 resonance effect causing the standing wave patterns at the absorption peaks and the gradient structure enhancing the absorbance, this novel ultrawideband multilayer planar absorber offers a promising solution for practical applications.