Accurate equivalent circuit design of an ultra-broadband composite absorber

The combination of circuit analog absorber (CAA) and honeycomb absorbing material (HAM) has the advantages of lower profile, wider absorption bandwidth, and strong absorption performance. However, the increase in the number of CAA interlaced with various dielectric spacers makes the design and optimization of this complex multi-layer structure more difficult. Here, an accurate equivalent circuit model (ECM) of the multi-layer lossy single-square loop (SSL) metal-grounded is developed, which can be used to quickly design and optimize absorbers with the aid of genetic algorithm (GA). Based on the guideline, a lightweight composite absorber consisting of a double-layer impedance-sheet CAA at the top and a HAM at the bottom is developed. It covers an ultra-wideband -10 dB reflection reduction in the frequency band of 0.83 to 18 GHz with a fractional bandwidth of 182% in a total thickness of 35 mm and only 4% over the minimum thickness calculated by the Rozanov limit. The CAA is responsible for the absorption at a lower frequency, while the HAM absorbs the incident electromagnetic waves at the higher end of the frequency spectrum. The agreement between the experimental and simulated results verifies the viability of our design approach.