Abstract
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 lambda/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.